Extend the reference library with assembly-level and runtime reading
Add references/assembly-idioms.md: the x86/x64 conventions, frame and epilogue fingerprints, string-instruction and x87 idioms, virtual dispatch, and WOW64 path redirection, each stated with what it changes about reading or patching a routine. Add the managed-decompilation, Unity IL2CPP and packaged-Python references, with the capability registry, host-probe and plan entries they depend on. Register all four in the routing index, symptom table, route inventory, coverage and evidence records, and add P37 for a 32-bit target's registry and file views.
This commit is contained in:
root
@@ -136,7 +136,9 @@ an evidence record.
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What it covers, and what it deliberately does not, is stated in the skill itself
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(`skills/exe-reverse/references/coverage-and-limits.md`). The short version: Windows PE on x86 and
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x64, deep on the layers that have been worked through — triage, patching, signatures, licensing
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classification, protectors, managed code, and the hardware-observation route map. Defeating a
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classification, protectors, managed code, and the hardware-observation route map. Two
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application-runtime layers — Unity IL2CPP metadata recovery and packaged Python — are documented
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from public write-ups, and are graded `unverified` for that reason. Defeating a
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server-side authority, a fully automated general-purpose devirtualiser, defeating a named commercial
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protector as a product claim, and any guarantee on a Windows build this repository has not measured
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are **not** covered, and the skill is written to say so and stop rather than apply the nearest
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@@ -176,6 +178,8 @@ exercise.
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---
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Proudly supported by the [LINUX DO](https://linux.do) community.
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## Disclaimer
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The material is provided *as is*, without warranty of any kind. Results are recorded as they were
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+4
-1
@@ -103,7 +103,8 @@ export EXEREV_TOOLS=<dir>:<dir> # POSIX
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它覆盖什么、刻意不覆盖什么，写在 skill 自身（`skills/exe-reverse/references/coverage-and-limits.md`）。
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简版：Windows PE 的 x86 与 x64，在真正做过的层上做得深 —— 初筛、补丁、特征码、授权归类、壳、托管代码，
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以及硬件观测的路线图。服务端权威的破解、通用自动化去虚拟化器、把"攻破某个具名商业保护产品"作为
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以及硬件观测的路线图。另外两层应用运行时 —— Unity IL2CPP 的元数据恢复与打包后的 Python —— 依据公开
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文章整理，因此标记为 `unverified`。服务端权威的破解、通用自动化去虚拟化器、把"攻破某个具名商业保护产品"作为
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产品级宣称，以及对本仓库未测量过的 Windows 版本做任何保证，都**不在**覆盖内，而 skill 被写成如实说明
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并停下，而不是把最近的一份文档流程套到一个它并非为此而写的目标上。
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@@ -137,6 +138,8 @@ push 时跑完整套：六道门、Python 3.11–3.14 的测试矩阵、以及 l
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---
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Proudly supported by the [LINUX DO](https://linux.do) community.
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## 免责声明
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材料按"原样"提供，不附带任何形式的担保。结果是在一台机器、某一时刻测得的；这里不承诺某条路线在你
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@@ -1,6 +1,6 @@
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---
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name: exe-reverse
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description: "Reverse engineer, patch, and analyse Windows x86/x64 local software. Use for an .exe/.dll/.sys/.msi sample, a licence check or feature gate that must be located, a binary that must be patched and still run, a target that fights analysis, or a request to decide whether a client-side change can work at all. Covers PE structure and triage, equal-length byte patching, AOB signature work, debugging and injection, dump and repair, licensing-mechanism classification, algorithm and key recovery, packers and code virtualisation, managed .NET assemblies, kernel drivers, and the hardware-observation routes (instruction tracing, hardware breakpoints, ETW) that software tooling cannot substitute for."
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description: "Reverse engineer, patch, and analyse Windows x86/x64 local software. Use for an .exe/.dll/.sys/.msi sample, a licence check or feature gate that must be located, a binary that must be patched and still run, a target that fights analysis, or a request to decide whether a client-side change can work at all. Covers PE structure and triage, equal-length byte patching, AOB signature work, debugging and injection, dump and repair, licensing-mechanism classification, algorithm and key recovery, packers and code virtualisation, managed .NET assemblies, Unity IL2CPP builds, packaged Python programs, kernel drivers, and the hardware-observation routes (instruction tracing, hardware breakpoints, ETW) that software tooling cannot substitute for."
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license: MIT — see LICENSE at the repository root
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compatibility: "Python 3.10+. Static PE analysis and byte patching are offline and dependency-free. Debugging needs a debugger installed; kernel, driver and instruction-trace routes need test signing, a second machine, or specific processor support. Run scripts/hwprobe.py first: it reports what this host can actually do rather than what is generally possible."
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metadata:
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@@ -146,6 +146,12 @@ Load the named file **before your next command**, not after your next three atte
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| Your signature-based patch worked on one version and misses on the next | `references/aob-and-signatures.md` |
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| Two supposedly identical builds behave differently | `references/pe-diff-and-versions.md` |
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| The target is a .NET assembly and hex-patching it does nothing | `references/managed-dotnet.md` |
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| A .NET assembly decompiles, but the names are gone or the C# does not add up | `references/dotnet-decompilation.md` |
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| A Unity game's `global-metadata.dat` is missing, empty or unreadable beside its `GameAssembly.dll` | `references/unity-il2cpp.md` |
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| il2cppdumper reports `CodeRegistration : 0`, or the metadata version disagrees with the struct it parses | `references/unity-il2cpp.md` |
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| A hot-update assembly decompiles to high-entropy IL, or an AssetBundle refuses to open | `references/unity-il2cpp.md` |
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| The target directory holds `python3xx.dll`, `_internal` or `pyarmor_runtime` | `references/python-runtime-bundles.md` |
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| A Python module is high-entropy while the rest of the packaged program is ordinary | `references/python-runtime-bundles.md` |
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| The payload holds a large `data/app.so` and hardly any native code | `references/flutter-and-dart-aot.md` |
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| The sample is an installer, and the interesting binary is nowhere on disk after install | `references/installers-and-packaging.md` |
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| The file is a driver, or it refuses to load without a driver present | `references/kernel-and-drivers.md` |
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@@ -156,6 +162,9 @@ Load the named file **before your next command**, not after your next three atte
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| A tool returns more output than you can read, or the same run returns different amounts | `references/toolchain.md` |
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| The binary was produced by a compiler you have not identified | `references/compiler-fingerprints.md` |
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| The target is written in Go, Rust or Delphi and the call structure looks wrong | `references/compiler-fingerprints.md` |
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| A detour or code cave crashes its callee, or the arguments arrive at wrong offsets | `references/assembly-idioms.md` |
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| A 32-bit target's licence file or registry key is absent from the path the documentation gives | `references/assembly-idioms.md` |
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| A prologue does not look like the compiler the headers named | `references/assembly-idioms.md` |
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| You are about to conclude "it must be server-side" | `references/network-activated-licensing.md` |
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| You cannot tell whether a failure is your patch or the target's own behaviour | `references/verification.md` |
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| You are about to write off a route as impossible | `references/protectors-and-packers.md` |
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@@ -175,7 +184,7 @@ loudly — it produces an artifact that runs and does the wrong thing.
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|---|---|---|
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| 1 | **Is it packed or protected?** Sections near-zero entropy or flat-high, imports that resolve to almost nothing, an entry point that lands in a stub | Whether you can read the code at all yet, and whether patching is even the right instrument |
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| 2 | **Where does the behaviour live?** Client logic · server-issued data the client renders · a server-authoritative decision | Whether a local change can work, can appear to work, or cannot work. Decide this early — it is the most expensive wrong turn here |
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| 3 | **Native, managed, or a runtime bundle?** PE with a CLR directory, Go/Rust static binary, or packed runtime | The whole toolchain. Hex-patching a .NET assembly is a different activity from patching C++ |
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| 3 | **Native, managed, or a runtime bundle?** PE with a CLR directory, Unity IL2CPP, a packaged Python program, Go/Rust static binary, or packed runtime | The whole toolchain. Hex-patching a .NET assembly is a different activity from patching C++, and "the names are in another file" is a different activity from both |
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| 4 | **What must the deliverable do?** Write it as a testable sentence, then name its form | The most expensive drift. A live result presented as a finished artifact is the same failure as a wrong patch |
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| 5 | **Does it verify its own bytes, or its signature?** Checksums, section hashes, page guards, Authenticode, embedded digests | Whether patching the file is viable at all, or whether the answer is a memory patch or a report |
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| 6 | **What host do you actually have?** Debugger installed, elevation, a hypervisor present, test signing, a second machine | Which routes exist. Run the host probe rather than assuming |
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@@ -199,10 +208,13 @@ is the most common way an hour disappears.
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|---|---|---|
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| A PE on disk, unknown | `scripts/pe_triage.py` — headers, sections, imports, entropy, fingerprints | `references/recon.md` |
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| A byte or a branch that must change | `scripts/pepatch.py` — equal-length, verified, dry-run first | `references/patching.md` |
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| Code a detour, stub or cave must run through | The convention and the frame first: shadow space, alignment, and the epilogue the trampoline must preserve | `references/assembly-idioms.md` |
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| The same patch across several versions | `scripts/aob_scan.py`, then its `--across` mode against the other build | `references/aob-and-signatures.md` |
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| Runtime behaviour to be located | A debugger, then hardware breakpoints if software ones are detected | `references/dynamic-debugging.md` |
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| Code that cannot be read at all | Protector identification, then the unpack route | `references/protectors-and-packers.md` |
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| A .NET assembly | Managed tooling; do not start with a hex editor | `references/managed-dotnet.md` |
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| Unity IL2CPP (`GameAssembly.dll` + metadata) | Classify the metadata placement before any patch; the names and the code are separate files | `references/unity-il2cpp.md` |
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| A packaged Python program | Identify the packager and the interpreter version first; both decide whether anything else is readable | `references/python-runtime-bundles.md` |
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| An installer or a packaged app | Extract first, then re-triage what came out | `references/installers-and-packaging.md` |
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| A licence decision to classify | The mechanism taxonomy, before any patching | `references/license-mechanisms.md` |
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| A driver or kernel component | Kernel route; user-mode tooling stops at the boundary | `references/kernel-and-drivers.md` |
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@@ -0,0 +1,238 @@
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# Assembly-level reading: the ABI, the frame, and the idiom
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Goal: turn a listing into three facts you can act on — which convention moves the arguments, which
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producer shaped the frame, and which library routine an instruction sequence is standing in for —
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before deciding where to patch and what the patch must preserve.
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## When to load this
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Load this when a routine's parameters or return value do not line up with the convention the
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toolchain implies; when a detour, stub or code cave must keep its callee working; when a prologue does
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not match the compiler the headers named; when a body is dense with string instructions or
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floating-point stack operations; when a virtual call has no direct target; and when a 32-bit target's
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file or registry access does not land where the documentation says it should.
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Grades: the conventions and encodings are documented architecture, and applying one to a listing is
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`inferred`. Any statement about what a particular build emits is `unverified` until it is checked
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against that build. No sample was disassembled to write this file, so every row is a shape to look
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for, not a measurement.
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## The calling convention is the first thing the listing tells you
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**32-bit.** The convention decides where the parameters are, who removes them, and therefore how many
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the callee expects. `ret` with an immediate is the cheapest parameter count in the whole file: the
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number is the byte count of the arguments the callee pops.
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| Convention | Arguments | Stack cleaned by | Return | Where it turns up |
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|---|---|---|---|---|
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| `cdecl` | right to left, all on the stack | caller, `add esp, N` after the call | EAX | C and C++ default; every variadic function |
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| `stdcall` | right to left, all on the stack | callee, `ret N` | EAX | the Win32 API; most exported callbacks |
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| `fastcall` | ECX, EDX, then the stack | callee, `ret N` | EAX | `__fastcall`, some optimised exports |
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| `thiscall` | ECX is `this`, the rest on the stack | callee, `ret N` | EAX | Microsoft C++ member functions |
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| register convention | EAX, EDX, ECX in order | callee | EAX | Borland-family C++ and Delphi builds — `unverified` until a known sample confirms it |
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A caller that cleans the stack is also the caller that must know the argument count statically, which
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is why a variadic `cdecl` call is recognisable from the `add esp` after it rather than from the callee.
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**64-bit.** Four integer arguments in RCX, RDX, R8, R9 and four floating-point arguments in
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XMM0-XMM3; the rest at `[rsp+0x20]`, `[rsp+0x28]`, … — the first 32 bytes above the return address
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belong to the callee as **shadow space** for exactly those four registers. The caller allocates and
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frees it, and RSP is 16-byte aligned at the `call`, so a callee enters with `rsp % 16 == 8`. RAX
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returns the integer result and XMM0 the floating-point one. Volatile: RAX, RCX, RDX, R8-R11 and
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XMM0-XMM5. Non-volatile: RBX, RBP, RDI, RSI, RSP, R12-R15 and XMM6-XMM15.
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Five consequences, and the first three are where hand-written patches break:
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- **A cave that calls needs a frame.** `sub rsp, 0x28` before the call and `add rsp, 0x28` after it is
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the minimum shape: 32 bytes of shadow space plus alignment. A cave that calls with RSP untouched
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gives the callee an unaligned stack, and the failure surfaces inside the callee's first aligned
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SSE store, not at the call.
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- **The home space is live.** A callee may spill RCX-R9 into `[rsp+8]`..`[rsp+0x20]` as its first
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act. A trampoline that overwrites those slots before running the original prologue destroys the
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arguments it was supposed to forward.
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- **The fifth argument is at `[rsp+0x28]`, not `[rsp+0x20]`.** The four slots of the shadow area
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hold the register arguments, and the stack arguments begin after them; measuring from the return
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address is what shifts the first one by eight bytes.
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- **Non-volatile means what it says.** A stub that uses RBX, RDI, RSI or R12-R15 must save and restore
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them. A stub that uses only RAX, RCX, RDX, R8-R11 may not.
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- **Read the count from the accesses, not from the convention.** The register count bounds the
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parameters; it does not prove the function uses all four, and a decompiler that fills the unused
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slots with plausible types is guessing.
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**Varargs on 64-bit** duplicate a floating-point argument in both its XMM register and its integer
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register, so a `printf`-style call shows the same value moved twice. That is not a bug in the listing
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and not a second argument.
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## Frames: what the prologue says about the producer
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The frame is the most reliable statement of provenance in a listing, because a compiler emits the same
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shape for every function it builds and an assembler author emits a different one every time.
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| Shape in the listing | Producer | What it changes |
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|---|---|---|
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| `push ebp; mov ebp, esp; sub esp, N` | 32-bit build with the frame pointer kept — debug, or a function that needs a stable frame | locals at `[ebp-N]`, arguments at `[ebp+8]` upward; the frame can be reconstructed with confidence |
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| `sub esp, N` with no EBP use at all | 32-bit release build with frame-pointer omission | locals are at `[esp+N]`, and any comment naming `[ebp-x]` comes from a different build |
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| `push ebx`/`esi`/`edi`, then a mirrored pop set and `mov esp, ebp; pop ebp; ret` | ordinary compiler epilogue | the epilogue is the only place the frame is unwound; a patch that jumps past it unbalances the caller's stack |
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| `lea edi, [ebp-N]; mov ecx, N/4; mov eax, 0CCCCCCCCh; rep stosd` | Microsoft debug build | 0xCC is `int3` fill: a run of `int3` inside a function body is uninitialised stack, not code and not a trap |
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| `enter N, 0` … `leave` | hand-written assembler, or a build asked for it explicitly | no mainstream compiler emits `enter`; treat the routine as assembled and read its author's intent, not a compiler's |
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| `ret 4`, `ret 8`, `ret 0Ch` | 32-bit `stdcall` or `thiscall` callee | parameter byte count on the spot; this encoding does not exist in 64-bit mode, so seeing it dates the image to 32-bit |
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| no prologue, body under five bytes, plain `ret` | leaf function, or a stub | nothing to preserve — and too short for a five-byte jump, which is a hooking constraint, not a reading one |
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| `mov [rsp+8], rcx` near the entry (64-bit) | debug build, or a function that must keep its arguments in memory | the home-space spill is the frame; RBP being untouched does not mean the frame is absent |
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| `push rbp; mov rbp, rsp; sub rsp, N` (64-bit) | frame pointer forced — debug, or a function with unwinding requirements | the same reconstruction rules as 32-bit, with the frame sized so that RSP stays 16-byte aligned |
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| a push/pop set larger and more symmetric than the callee-saved set | hand-written routine | the author preserved registers by habit; check the epilogue mirrors it exactly |
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Two conventions of the assembler itself are worth knowing when the artifact *is* assembly rather
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than a compilation: `USES` generates the push/pop pair for the registers it names, and `LOCAL`
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generates the `sub esp` for its variables, so a routine whose frame looks minimal in source still has
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a full one in the listing. A routine whose only frame is what a macro produced is still a frame you
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must respect when patching.
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**What a frame tells you about patching.** A five-byte jump over a prologue also jumps over the
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`sub esp` and the pushes, and the callee's epilogue will undo work that never happened. Hook the
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first instruction of the function, not the first instruction after the frame, or run the displaced
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bytes in a trampoline and jump back past them. The instruction-length problem itself belongs to
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`references/injection-and-hooking.md`; the frame is why the length is not the only thing that must
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match.
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## String instructions: a library routine written out in one instruction
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| Instruction | Stands in for | Registers | Tell |
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|---|---|---|---|
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| `rep movsb` / `rep movsd` | forward `memcpy` | RCX count, RSI source, RDI destination | the copy loop is absent; one instruction does the whole transfer |
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| `rep stosb` / `rep stosd` | `memset`, including zero-fill | AL/EAX value, RCX count, RDI destination | a buffer is cleared without a loop and without a `VirtualAlloc`-zeroing call |
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| `repne scasb` | `strlen` | AL = 0, RDI string, RCX = -1 as the bound | the length is found by scanning, and RCX ends negated |
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| `repe cmpsb` | `memcmp` / `strncmp` | RSI and RDI, count in RCX | equality is decided by the string unit, ZF read after the prefix |
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| `std` before `rep movs`, `cld` after | a backward or overlap-aware copy | DF = 1 | a compiler almost never emits this; a hand-written routine doing it might |
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Consequences that change a measurement:
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- **The same routine may be an SSE/AVX loop instead.** A compiler is free to inline `memcpy` as wide
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loads and stores, and a modern C runtime is free to use `rep movsb` because the processor implements
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it efficiently. Presence of a string instruction says "this is a library-shaped routine", not "this
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build is old" — the dating claim needs a compiler fingerprint, not an instruction.
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- **One instruction, many iterations.** A trace, a single-step or a breakpoint at a `rep` address sees
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one event for a whole buffer. Counting executions there undercounts the work, and a hook that
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instruments per iteration sees nothing per iteration at all. The repeated-instruction hazard for
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memory hooks is described in `skills/exe-reverse/evidence/tool-sources.md`.
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- **A zero count is a legal no-op.** `rep movs` with RCX = 0 copies nothing and does not fault. "The
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copy instruction is present" is not "the data was copied"; read RCX before believing either.
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- **Direction flag.** The ABI requires DF clear on entry and exit. A hand-written stub that sets it
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and does not clear it corrupts the next library call, and the crash appears in unrelated code,
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which is the classic shape of an unattributable failure.
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## x87: the floating-point stack, and what its presence means
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x87 is a stack of eight extended-precision registers, ST(0) through ST(7), with ST(0) on top.
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Loads push, stores pop, and arithmetic consumes its operands and pushes a result. That is why a
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listing shows `faddp` and `fmulp` with no operands.
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| Instruction | What it does |
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|---|---|
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| `fld dword ptr [x]` / `fld qword ptr [x]` | push a float or a double |
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| `fild dword ptr [n]` | push an integer, converted to extended precision |
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| `faddp`, `fmulp`, `fsubp`, `fdivp` | pop two, push the result |
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| `fstp dword ptr [x]` | pop into memory |
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| `fcomip st, st(1)`, `fucomip` | compare, pop, and set EFLAGS so an ordinary `jcc` follows |
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| `fldz`, `fld1`, `fldpi` | push a constant — there is no immediate form |
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| `fchs`, `fabs` | sign manipulation, usually around a threshold test |
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| `fsin`, `fcos`, `fpatan`, `fsqrt` | transcendental and root operations — angle and distance math |
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What the presence means:
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- **x87 in a 64-bit image is not compiler output.** The 64-bit Microsoft toolchain uses SSE2 as its
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baseline and does not emit x87 for C or C++ floating-point work, and it does not support inline
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assembly at all. x87 there points at a hand-written routine, an embedded library built elsewhere,
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or a toolchain outside that family — an inference worth checking against the imports before acting.
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- **x87 in a 32-bit image is ordinary**, and it is a weak dating signal at best.
|
||||
- **A float comparison is patchable like an integer one.** `fcomip` plus `jcc` is the same branch
|
||||
shape as `cmp` plus `jcc`, so the site choice is unchanged. The *constant*, though, lives in a data
|
||||
section; a byte patch on it changes the threshold everywhere it is read.
|
||||
- **Operand order is the usual decompiler error.** `fsubp` and `fsubrp` reverse which operand is
|
||||
subtracted from which, and a decompiler that renders a subtraction from a stack it did not fully
|
||||
model can invert it. Read the two pushes that precede the operation before trusting the sign.
|
||||
|
||||
## Virtual calls, object layout, and the three places a patch can go
|
||||
|
||||
In a Microsoft C++ build the object begins with a pointer to its class's **virtual function table**;
|
||||
the table holds the virtual functions in declaration order, one pointer per slot. The call is an
|
||||
indirect transfer, so it has no static target:
|
||||
|
||||
mov rax, qword ptr [rcx] ; the vptr, RCX is this
|
||||
call qword ptr [rax+8] ; slot 1
|
||||
|
||||
The displacement divided by the pointer width is the slot index. When RTTI is enabled, the slot
|
||||
before the vptr (`vptr[-1]`) points at the class's type information, which gives a class name
|
||||
without symbols — a static-analysis gain that costs one pointer read.
|
||||
|
||||
| Site to patch | What changes | Cost |
|
||||
|---|---|---|
|
||||
| the function body | every caller, virtual and direct | a routine with many callers is a helper, not a gate (`references/patching.md`) |
|
||||
| the vtable slot | this class, and every derived class that does not override the slot | the table is usually in a read-only section, so the write needs a protection change, and a file patch has to change the section's characteristics |
|
||||
| the call site | one call, leaving every other user intact | only viable when the site is unique, and it breaks when the object's dynamic type changes |
|
||||
|
||||
Two reading cautions. A virtual call is an indirect transfer, so the listing has no successors until
|
||||
you read the table, and the table is data (`references/static-analysis.md`). And teaching examples
|
||||
that model the vtable pointer as a named first field, or place it before the object, model the
|
||||
mechanism rather than the ABI: in a real Microsoft build the vptr is at offset 0 and the first data
|
||||
member follows it, which is what the decompiler will show.
|
||||
|
||||
## WOW64: the two views a 32-bit target actually uses
|
||||
|
||||
A 32-bit process on a 64-bit Windows runs under WOW64, and its file and registry paths are redirected
|
||||
so that both bitnesses can coexist. The redirection is silent: the call succeeds, the path looks
|
||||
right, and the bytes are somewhere else.
|
||||
|
||||
| The target asks for | A 32-bit process gets | A 64-bit process gets |
|
||||
|---|---|---|
|
||||
| `%SystemRoot%\System32\foo` | `%SystemRoot%\SysWOW64\foo` | the real `System32` |
|
||||
| `%SystemRoot%\Sysnative\foo` | the real `System32` — a virtual path that exists only for 32-bit callers | not a directory |
|
||||
| `HKLM\SOFTWARE\Vendor` | `HKLM\SOFTWARE\Wow6432Node\Vendor` | `HKLM\SOFTWARE\Vendor` |
|
||||
| `HKCR\CLSID\{…}` | the 32-bit COM registration view under the same node | the native view |
|
||||
|
||||
What this changes during analysis:
|
||||
|
||||
- **"The key is not there" is a statement about the view.** Both views exist on the same machine, and
|
||||
a native-view search that returns nothing has excluded one view, not the configuration. Open the
|
||||
32-bit registry editor, or query the `Wow6432Node` path, before concluding that the target keeps
|
||||
no local state — that conclusion otherwise redirects the whole investigation to a server.
|
||||
- **The file twin matters for anything the target loads.** A 32-bit target loads the `SysWOW64` copy
|
||||
of a system library even when an installer wrote the other one, so a replaced file can be present
|
||||
and unused, and a missing file can be present under the other name.
|
||||
- **Bitness decides the debugger, not the file header.** A 32-bit target needs a 32-bit debugger or a
|
||||
WOW64-aware one, and its register set and PEB are the 32-bit ones. Query the process architecture
|
||||
(`IsWow64Process2`) rather than inferring it from the image, because a managed AnyCPU image and an
|
||||
emulated host both defeat the header.
|
||||
- **Elevation adds a second redirect.** A 32-bit process without a manifest that writes under
|
||||
`HKLM\SOFTWARE` or `Program Files` is also subject to UAC virtualisation, which lands the write in
|
||||
a per-user store. A setting that "was written successfully" and cannot be found afterwards can be
|
||||
in either of two places; check both before calling the write a failure.
|
||||
|
||||
## Idioms worth recognising on sight
|
||||
|
||||
| Listing | Means |
|
||||
|---|---|
|
||||
| `xor eax, eax` | zero a register, or return success — shorter than a move and extremely common in a check that passed |
|
||||
| `test eax, eax` or `or eax, eax` | compare with zero through SF and ZF; a literal `cmp eax, 0` is the rarer form |
|
||||
| `lea eax, [eax+eax*2]` | multiply by three: `lea` is arithmetic, not only address formation |
|
||||
| `lea rax, [rip+disp]` | the address of a global or a literal — the 64-bit cross-reference |
|
||||
| `call qword ptr [rip+disp]` | an imported API or a function pointer slot, which is the import table in one instruction |
|
||||
| `mov rax, gs:[60h]`, `mov eax, fs:[30h]` | the process environment block: the shape of an anti-debug read or a manual API resolution walk |
|
||||
| `movzx` / `movsx` | the value is narrower than the register, and the extension tells you how it is treated: zero-extended is unsigned or a table index, sign-extended feeds signed arithmetic and negative bounds |
|
||||
| `setne al` / `cmovne` | a boolean materialised without a branch — a one-byte patch changes its polarity |
|
||||
| `int 3` (0xCC) | padding, a debug build's uninitialised stack fill, or a breakpoint: three meanings, one byte |
|
||||
| `ud2` | the compiler's marker for unreachable code, or a deliberate trap |
|
||||
| `jmp rax` after a table load | a dispatch whose target set is data, not code |
|
||||
| a push/pop pair around a single call | a volatile register saved across the call — compiler output, not a frame |
|
||||
|
||||
## What this file does not do
|
||||
|
||||
- **An idiom is not an identity.** Recognising that a shape is a copy, a comparison or a dispatch does
|
||||
not say which routine owns the decision. That is `references/static-analysis.md`, and the owner is
|
||||
confirmed by observation, not by reading (`references/dynamic-debugging.md`).
|
||||
- **No disassembler is shipped here.** The reading is done with whatever the host provides, and
|
||||
`scripts/hwprobe.py` reports whether that is anything at all.
|
||||
- **A reconstructed frame is a hypothesis.** The listing gives the shape a compiler intended; the
|
||||
unwinder gives the one the processor used. Where they disagree, the run is authoritative.
|
||||
- **Conventions describe calls the compiler emitted.** A stub written by hand, a callback invoked by
|
||||
the system, and an exported function called from another language each need their convention
|
||||
confirmed from the call site, not assumed from the language the target is written in.
|
||||
@@ -31,6 +31,11 @@ Three fingerprints survive most builds and are worth checking first.
|
||||
- The **debug directory** and its CodeView record carry a symbol-file name and a build-time GUID
|
||||
(`pe-structure.md`, "The debug directory and the PDB path").
|
||||
|
||||
Two further fingerprints are read from instructions rather than from headers: whether the frame,
|
||||
the register use and the epilogue match a compiler at all, and whether floating-point work went
|
||||
through the x87 stack or through SSE. `references/assembly-idioms.md` carries the shapes and what each
|
||||
one changes about reading the routine; both are `inferred` until a second signal confirms the toolchain.
|
||||
|
||||
## MSVC
|
||||
|
||||
**Observed.** This host's system images were built by Microsoft's toolchain: `notepad.exe` and
|
||||
|
||||
@@ -41,6 +41,7 @@ named gap.
|
||||
| Direction | Strongest defensible grade | What it rests on | Dependency not shipped here |
|
||||
|---|---|---|---|
|
||||
| Static PE structure analysis | `observed` for the reader; `unverified` per target | the shipped reader (`scripts/peutil.py`) parses the DOS header and stub, compiler fingerprint, NT and optional headers, data directories, sections, both offset directions, imports, delay imports, exports, resources, base relocations, TLS callbacks, debug directory and CodeView/PDB, load configuration, the certificate table location, a recomputed file checksum and per-section entropy (`observed`: a summary run over a local sample returned architecture, signature state, declared-versus-computed checksum agreement and the populated directory set) | a disassembler or decompiler for anything past the headers; a second reader when two tools disagree about one field |
|
||||
| Instruction-level reading | `inferred` | the calling conventions, frame shapes and idiom meanings are documented architecture and toolchain behaviour, stated in `references/assembly-idioms.md` so a listing can be checked against them; no target was disassembled here | a disassembler or decompiler, and a build whose toolchain is known — the producer claim stays `inferred` until a second fingerprint agrees |
|
||||
| Byte patching | `observed` for the patcher's guards; `unverified` on any target | the shipped patcher (`scripts/pepatch.py`) opens the input read-only, writes a new file, refuses a length change without an explicit flag, refuses an ambiguous pattern, pins the expected bytes, re-parses its own output and re-reads every patched byte, and recomputes the checksum (`observed`: a dry run printed the site, the byte pair, the unproven-length note, and wrote no output file) | a debugger, to establish that the patched site is the site that executes |
|
||||
| AOB pattern work | `observed` as a matching rule; `inferred` as a method | a three-byte pattern matched 64 sites and the tool refused the patch, naming three ways out (select an index, accept all, or extend the pattern with context); exact-once is the default (`observed`) | a disassembler, to argue that a pattern's identity is stable across the builds that matter |
|
||||
| Dynamic debugging workflow | `unverified` | the route is described and a debugger exists on at least one host; no breakpoint log, stepping session or debugger transcript is recorded in this repository | an interactive debugger, and a target you are permitted to run |
|
||||
@@ -54,7 +55,9 @@ named gap.
|
||||
| Managed (.NET) code | `observed` as classification; `unverified` for recovery | the runtime header is data directory index 14, the shipped reader carries that index and reports the populated directory set, so "this artifact is managed" is measurable | a metadata and intermediate-language toolchain, plus a runtime to test against |
|
||||
| Anti-analysis | `inferred` | the decision procedure is described: identify, measure the cost, prefer static, keep observers separate from interceptors; nothing here was measured on a target that detects observers | a second machine, and a target you can afford to lose |
|
||||
| Protectors and packers | `inferred` | the reader measures per-section entropy and documents it as a heuristic rather than a verdict, and documents following a packer as a non-goal; no protected image was analysed here | protector-specific tooling, and a decision about whether buying it is justified |
|
||||
| Code virtualization and flattening | `unverified` | the shapes are described; no virtualized target was analysed here | a devirtualizer, which in practice is the reader's own budget |
|
||||
| Code virtualization and flattening | `unverified` | the shapes and the interpreter's anatomy are described, the latter from public write-ups of one protector family; no virtualized target was analysed here | a devirtualizer, which in practice is the reader's own budget |
|
||||
| Unity IL2CPP runtime layer | `unverified` | the layer map, the metadata placements and the registration failure modes are described from public write-ups; no IL2CPP build was opened here, and the shipped reader proves only that the outer file is a PE | an il2cpp dumper or equivalent, the build itself, and a host that can run it when the metadata must be dumped rather than read |
|
||||
| Python-packaged software | `unverified` | the packager shapes and the code-object wrapper's mechanisms are described from a public write-up; no packaged Python program was unpacked here | the packager's extractor, an interpreter at the exact version, a decompiler, and the wrapper's own version where one is present |
|
||||
| Symbolic execution and deobfuscation | `unverified` | an engine may exist on a host and is reported by the probe (`observed` for that inventory); no result from one is recorded | a symbolic execution engine, and a way to bound the search |
|
||||
| Kernel and driver analysis | `unverified` | the host probe (`scripts/hwprobe.py`) reports driver load as gated on reboot-and-test-signing and warns that enforced code integrity may refuse an unsigned driver regardless of boot flags (`observed` as the repository's own statement); no driver was built or loaded here | a signing path or a test-signing machine, a second host for debugging, and a driver toolchain |
|
||||
| Hardware tracing | `unverified` | the probe reports trace support as gated on a capture path even where the CPU advertises support, names decoding as the lesser constraint, and reports branch-record reads as needing kernel or hypervisor privilege (`observed` as the repository's own statement); no trace was captured here | a supported CPU, a capture path, and a decoder |
|
||||
@@ -77,6 +80,11 @@ by applying a procedure to a target it was never written for.
|
||||
performs is not, and no amount of client-side work substitutes for it.
|
||||
- **A fully automated general-purpose devirtualizer.** There is no such capability here, neither
|
||||
for a commercial protector nor for a custom bytecode interpreter.
|
||||
- **Decrypting a container whose cipher is itself virtualised.** Where a metadata file or a code
|
||||
object is held by a bytecode interpreter that runs before the plaintext exists, the route is to
|
||||
dump after that interpreter has run, or to implement it; nothing here decrypts it by reading.
|
||||
- **A general unpacker for a versioned code-object wrapper.** The mechanism is described; a tool
|
||||
that covers a version this repository has not seen is a research task, not a command.
|
||||
- **Defeating a specific commercial protector as a product claim.** No row above asserts that any
|
||||
named protector falls to any route. Naming a protector is a classification result; whether it
|
||||
yields is a per-target measurement that must be made, with its result recorded.
|
||||
|
||||
@@ -25,13 +25,28 @@ becomes `run` only when someone runs it and records the output.
|
||||
| PE structure reading | answering any header, section, directory, import, export, resource, TLS, relocation or checksum question | Python only — offline and dependency-free | `run` |
|
||||
| Triage | first contact with an unknown binary: identity, build evidence, protective signals, surface | Python only | `run` |
|
||||
| Toolchain fingerprinting | deciding which toolchain produced a binary, and what that implies for reading it | the binary; a disassembler only if the fingerprint is inconclusive | `run` for the header-level signals, `argued` for the toolchain-specific structure |
|
||||
| Instruction-level reading | reading a routine's convention, frame and idiom so that a patch or a detour preserves what the callee expects | a disassembler or decompiler — the repository ships none | `argued` |
|
||||
| Byte patching | making a change that fits an existing instruction or constant slot | Python only, plus a copy to write to | `run` |
|
||||
| Signature location | finding a site across builds rather than at one address | Python only; a second build for the comparison | `run` |
|
||||
| Build comparison | locating what changed between two builds | two builds | `run` |
|
||||
| Identity scanning | publishing derived material without publishing the target | Python only | `run` |
|
||||
| Managed assembly analysis | reading and changing a .NET assembly | managed tooling — the repository ships none | `mapped` |
|
||||
| Managed assembly analysis | reading and changing a .NET assembly | a decompiler or disassembler (`ilspycmd`, `ildasm`) to read it, `de4dot` for a renamed one, an assembler or dnSpyEx to change it — the repository ships none | `mapped` |
|
||||
| Installer and package extraction | getting at the payload of an installer without running it | extraction tooling; the container type decides which | `mapped` |
|
||||
|
||||
## Application-runtime routes
|
||||
|
||||
A packaged application adds a layer between the PE and the logic: an interpreter and its artifacts,
|
||||
a container, or a wrapper around the code. These routes are described from public write-ups and the
|
||||
tools' own documentation; none was run on an artifact in this repository.
|
||||
|
||||
| Route | For | Requires | Taken |
|
||||
|---|---|---|---|
|
||||
| Unity IL2CPP metadata recovery | a readable metadata file when the shipped one is missing, empty, or decrypted only in memory | the build; a debugger or an instrumentation runtime for the memory route; a dumper for the code half | `argued` |
|
||||
| IL2CPP registration and version repair | a dumper that reports no registration, or parses a struct that disagrees with the metadata version | a dumper whose version handling can be overridden, and the exports or call sites that lead to the registration | `argued` |
|
||||
| Packaged Python extraction | the code objects inside a packaged executable | the packager's extractor, and an interpreter at the exact version the package bundles | `argued` |
|
||||
| Code-object wrapper removal | bytecode that is encrypted per object, with a runtime that decrypts it | the wrapper's key derivation for its version, or a run in which the plaintext can be dumped | `argued` |
|
||||
| VM-protector boundary tracing | redirecting one decision inside a virtualised region without devirtualising it | a debugger with tracing, and the point where the virtual flag word is materialised | `argued` |
|
||||
|
||||
## Dynamic routes
|
||||
|
||||
| Route | For | Requires | Taken |
|
||||
|
||||
@@ -0,0 +1,453 @@
|
||||
# Reading a .NET assembly: decompilers, CIL, and the logic underneath
|
||||
|
||||
Goal: produce a defensible account of what a managed program does -- its inputs, its decisions and
|
||||
its effects -- using a decompiler for the shape and CIL for the truth.
|
||||
|
||||
**What this answers:** which of `de4dot`, `ildasm`/`ilasm`, ILSpy/`ilspycmd` and dnSpyEx to reach
|
||||
for; how to run each; how to read a CIL listing; what the compiler-generated names mean; and the
|
||||
sequence that turns a method body into a statement about business logic.
|
||||
|
||||
**When to load this:** after `managed-dotnet.md` has classified the artifact as an ordinary managed
|
||||
assembly and the task is to *understand* it -- a licence check to locate, a feature gate to explain,
|
||||
an algorithm to recover, or decompiler output that is unreadable, renamed, or does not add up.
|
||||
|
||||
**Not this file:** classification, bundles, ReadyToRun and Native AOT (`managed-dotnet.md`); the
|
||||
structural rules for a managed edit and its verification (`managed-dotnet.md`, `patching.md`);
|
||||
native code (`static-analysis.md`); a live debugging session (`dynamic-debugging.md`).
|
||||
|
||||
## The order of work
|
||||
|
||||
**R1 -- Decompile for the map, disassemble for the fact.** A decompiler turns a stack machine into
|
||||
C#-shaped text by guessing types and expressions. That guess is what makes a 300-method assembly
|
||||
navigable. It is also where the wrong answer comes from. Read C# to form a hypothesis, read the IL
|
||||
around the decisive branch to test it, and go back.
|
||||
|
||||
**R2 -- Start at a surface, never at a random method.** A surface is something observable: a menu
|
||||
item, an error string, a command-line flag, a file the program writes, a request it sends. Walk
|
||||
inward from it. Reading the assembly alphabetically has no stopping rule.
|
||||
|
||||
**R3 -- One question per load.** "What does this method return?" and "who calls it?" are different
|
||||
reads of the same file. Answer the one you asked before opening the next tool.
|
||||
|
||||
**R4 -- Write the hypothesis down, then try to kill it.** A reconstruction that exists only in the
|
||||
transcript cannot be checked by the next reader, including you after a context change.
|
||||
|
||||
**R5 -- The cleaned assembly is not the shipped assembly.** A deobfuscated file has different
|
||||
tokens, different names and possibly different types. Analysis may use it; a patch, a hash or a
|
||||
version comparison must go back to the original.
|
||||
|
||||
**R6 -- Every line of the logic map carries a grade.** `observed` (a tool printed it, or a run
|
||||
showed it), `inferred` (the step is reasoned), `unverified` (assumed). A map whose rows are all
|
||||
`inferred` is a reading list, not a finding.
|
||||
|
||||
## Tool roles
|
||||
|
||||
| Question | Reach for | What it gives | What it costs |
|
||||
|---|---|---|---|
|
||||
| What is in this assembly, and what does it reference? | `ilspycmd -l c`, `ildasm /text`, or the tree pane of either GUI | types, members, dependencies, resources -- the map | minutes, and no truth about behaviour |
|
||||
| What does this method do, in C#? | ILSpy (GUI) or `ilspycmd` | readable reconstruction, fast | it is a reconstruction; P22 |
|
||||
| Is this instruction sequence what I think it is? | `ildasm /text /tokens`, `ilspycmd -il`, dnSpyEx IL view | the actual body, tokens, exception clauses | slow to read; no types or names |
|
||||
| Where does this value come from at run time? | dnSpyEx debugger | breakpoints, locals, call stack, values | interactive; one session at a time |
|
||||
| What did the obfuscator do, and can it be undone? | `de4dot -d`, then `de4dot` | a classifier and, for supported protectors, a cleaned assembly | the output is a new artifact with new tokens |
|
||||
| Change one method and run it now | dnSpyEx IL editor, or `ildasm` -> edit `.il` -> `ilasm` | an executable experiment | the change lives in memory (dnSpyEx) or in a rebuilt file (ilasm); neither is the deliverable until verified |
|
||||
| Read a .NET assembly where no Windows tooling exists | `ilspycmd` (cross-platform), `monodis` | C# or IL on Linux/macOS | older or fewer framework references resolved |
|
||||
|
||||
The four GUI decompilers overlap and are not interchangeable in practice.
|
||||
|
||||
| Tool | What it is | Best at | Limits that change the plan |
|
||||
|---|---|---|---|
|
||||
| ILSpy / `ilspycmd` | ILSpy's own decompiler; GUI on Windows, Linux and macOS, plus a CLI | reading and navigating current assemblies; the CLI makes the same engine scriptable | the GUI is a human tool; the output is still a reconstruction |
|
||||
| dnSpyEx | a debugger first, with an assembly editor and an IL editor | breakpoints in decompiled code, locals, editing IL, in-memory images | Windows-only, GUI-only; not a tool an unattended run can drive |
|
||||
| dotPeek | JetBrains' free decompiler, built on ReSharper's engine | navigation and search, the compiler-generated-code toggle, Process Explorer, exporting a `.csproj`, acting as a symbol server for a Visual Studio debug session | Windows-only, GUI-only, no documented command line |
|
||||
| JustDecompile | Telerik/Progress decompiler | legacy assemblies, project export | **retired**: no new downloads and no support since 2024-04-02 (`observed`: the vendor page is now a discontinuation notice); use it only where it is already installed |
|
||||
|
||||
dotPeek is the one to reach for when the question is *navigation* rather than a single method.
|
||||
`observed`: JetBrains' feature page lists ReSharper-style *Find Usages* and *Go to Everything*,
|
||||
opening `.dll`/`.exe`/`.winmd`, archives and folders, a Process Explorer that lists a running
|
||||
process's modules and decompiles the managed ones, a *show compiler-generated code* toggle, an IL
|
||||
view synchronized with the C# view, project export, and a symbol-server mode that supplies a
|
||||
Visual Studio debugger with sources. It is free of charge.
|
||||
|
||||
JustDecompile is worth knowing about because it is still installed on some analysis machines, not
|
||||
because it is a route to plan. A retired tool receives no fixes for newer metadata, so a failure to
|
||||
open an assembly is the tool's age first and the target second.
|
||||
|
||||
None of the four is a substitute for reading the IL of the branch you care about.
|
||||
|
||||
## Setup, and the reference problem
|
||||
|
||||
`ilspycmd` installs as a .NET global tool:
|
||||
|
||||
```
|
||||
dotnet tool install --global ilspycmd
|
||||
ilspycmd --help
|
||||
```
|
||||
|
||||
`observed`: the ILSpyCmd README at version 11.0.0 states that the pointer package needs .NET SDK
|
||||
10.0.100 or newer, and that on Windows x64 and Linux x64 the tool is published as a Native AOT
|
||||
build. Pin a version for an older SDK; do not assume the newest package installs.
|
||||
|
||||
`observed`: `ildasm` and `ilasm` are documented as installed with Visual Studio, not with the
|
||||
runtime alone (Microsoft Learn, "Ildasm.exe" and "Ilasm.exe"). The .NET Core line distributes them
|
||||
separately from the SDK's default path, so "the SDK is installed" does not imply "ildasm is on
|
||||
PATH" -- check before writing it into a plan.
|
||||
|
||||
A missing reference is the most common reason decompiled output lies. When an assembly's dependency
|
||||
cannot be resolved, the decompiler renders the unknown type as `object`, drops members, or emits
|
||||
code that would not compile; the IL is unaffected. So:
|
||||
|
||||
- If the C# contains `object` where a domain type belongs, or members that "do not exist", read IL
|
||||
until the reference is supplied, or supply it.
|
||||
- ILSpy and dnSpyEx resolve dependencies from the target's directory and the GAC/runtime; a sample
|
||||
copied out of its install directory loses that context. Work on a copy of the *directory*.
|
||||
- Target framework matters for tool choice: an ILSpy old enough to predate a metadata feature
|
||||
cannot open the file, and `de4dot`'s dnlib predates the .NET Core era entirely (`inferred`:
|
||||
from the 2015 copyright range in its source and its obfuscator table; `unverified` per file).
|
||||
|
||||
## de4dot: the pre-pass, and its limits
|
||||
|
||||
`de4dot` is a deobfuscator and unpacker for the obfuscators it knows. `observed`: its README
|
||||
states GPLv3, no support, and a feature list that includes inlining, string and constant
|
||||
decryption, proxy-call removal, control-flow deobfuscation, resource and embedded-assembly
|
||||
decryption, tamper-detection and anti-debug removal, symbol renaming, and conversion of a wrapped
|
||||
Win32 PE back to a .NET PE.
|
||||
|
||||
Detect first. Detection is cheap, non-destructive, and tells you whether the rest is worth doing:
|
||||
|
||||
```
|
||||
de4dot -d sample.dll
|
||||
de4dot -d -r C:\samples -ru
|
||||
```
|
||||
|
||||
`observed`: the README documents `-d` as detect-only, prints "Unknown obfuscator" for an
|
||||
unsupported or unobfuscated file, and combines with `-r` (recursive) and `-ru` (ignore unknown
|
||||
files). Then deobfuscate into a separate directory, which is the shape the README recommends --
|
||||
copy the input tree to the output tree first, so unprocessed files survive:
|
||||
|
||||
```
|
||||
de4dot -r C:\samples -ru -ro C:\samples-cleaned
|
||||
```
|
||||
|
||||
`observed`: `-r`, `-ru` and `-ro` are the README's recursive form. For a single file the tool
|
||||
writes a new assembly rather than editing in place; in the builds in circulation the output name is
|
||||
the input's with a `-cleaned` suffix (`unverified`: not reproduced here, and the flag set of a
|
||||
2015-era tool is not stable across forks). List the directory after the run instead of assuming a
|
||||
name, and never point a later step at the input by habit.
|
||||
|
||||
What it cannot do, and what that means for the plan:
|
||||
|
||||
- **Names do not come back.** `observed`: the README says symbol renaming is impossible to restore
|
||||
because the original names are not in the assembly. A cleaned file gives readable *generated*
|
||||
names, not the vendor's. Every name in your notes is either original or yours; keep the
|
||||
distinction (see "Recovering names from evidence").
|
||||
- **Only the protectors in its table.** A protector newer than the tool, or a custom one, is
|
||||
"Unknown", and `-p un` handles it by preserving tokens and removing nothing (`observed`:
|
||||
README). That is a safe pass-through, not a deobfuscation.
|
||||
- **It is old.** The source's copyright range ends in 2015. Newer metadata, newer runtime
|
||||
features, and newer protector versions are outside what it was written against. A crash or a
|
||||
malformed output is the tool's age; it is not evidence that the target implements a defence.
|
||||
- **Dynamic decryption executes target code.** `observed`: the feature list includes decrypting
|
||||
strings and methods "statically or dynamically". Treat any dynamic mode as running the sample:
|
||||
isolate the host first (`environment.md`).
|
||||
- **The output is a new artifact.** Entry point, type list and tokens can change. Hash it, keep the
|
||||
original, and re-run classification rather than assuming the shape survived.
|
||||
|
||||
`observed`: the README also documents `--preserve-tokens`, `--keep-types` and
|
||||
`--dont-create-params` for the cases where a later step depends on token identity. Reach for them
|
||||
when you intend to patch, not when you intend to read.
|
||||
|
||||
## Reading the artifact before decompiling
|
||||
|
||||
The metadata is the map, and it costs one command.
|
||||
|
||||
```
|
||||
ilspycmd -l c sample.dll # entity kinds: c, i, s, d, e (class, interface, struct, delegate, enum)
|
||||
ilspycmd --list-resources sample.dll # embedded resources, .resources entries listed inside
|
||||
ilspycmd --dump-table TypeDef sample.dll # RID, token, names, heap offsets, coded indexes
|
||||
ilspycmd --dump-pdb sample.dll # debug information, if any
|
||||
ildasm /text /tokens sample.dll # whole assembly as IL, with metadata tokens
|
||||
ildasm sample.dll /out=sample.il # same, to a file
|
||||
```
|
||||
|
||||
`observed`: the option names and their wording are the `ilspycmd --help` text shipped with
|
||||
ILSpyCmd 11.0.0 (`-l`, `--list-resources`, `--dump-table`, `--dump-pdb`), and the
|
||||
`ildasm` switches are the Microsoft Learn parameter table (`/text`, `/tokens`, `/out=`,
|
||||
`/bytes`, `/raweh`, `/source`, `/linenum`, `/pubonly`, `/visibility:`).
|
||||
|
||||
Read in this order, and write down one line per answer:
|
||||
|
||||
1. **`.assembly extern`** -- what it depends on. A vendor licensing assembly, `System.Management`
|
||||
(WMI), `Microsoft.Win32.Registry`, `System.Net.Http`, a database client, a crypto library:
|
||||
each narrows the mechanism before a single method is read.
|
||||
2. **The type table** -- is there a `Licence`, `License`, `Activation`, `Trial`, `Auth`,
|
||||
`Settings`, `Config`, `ApiClient`? Names that survived are the cheapest evidence there is.
|
||||
3. **Custom attributes** -- `[DllImport]` names a native call, `[STAThread]` says WinForms,
|
||||
`[Route]`/`[HttpGet]` says ASP.NET, `[JsonPropertyName]`/`[DataMember]` names the wire
|
||||
fields, `[CommandLine]` names the flags. Attributes are strings that survived renaming more
|
||||
often than method names did.
|
||||
4. **String literals** -- a listing's `ldstr` operands are the domain vocabulary: error text,
|
||||
registry paths, URLs, SQL, file names, product names. Search them before reading control flow.
|
||||
5. **The entry point** -- `.entrypoint` in the IL, or the `Main` the manifest names. A library
|
||||
has none, which is itself the answer: the host owns the entry.
|
||||
|
||||
## How to read a CIL listing
|
||||
|
||||
### The shape of a method body
|
||||
|
||||
A body opens with a header (tiny or fat) that states the code size, the maximum stack depth, and
|
||||
whether locals and exception clauses follow. In text form:
|
||||
|
||||
```
|
||||
.method private hidebysig instance bool Check(string key) cil managed
|
||||
{
|
||||
// Code size 42 (0x2a)
|
||||
.maxstack 2
|
||||
.locals init (string V_0, bool V_1)
|
||||
...
|
||||
} // end of method App::Check
|
||||
```
|
||||
|
||||
- `.maxstack` and `.locals` are facts about the body, not about the source: the C# compiler's
|
||||
local count is not recoverable from them.
|
||||
- Exception handling is **not** in the linear instruction stream. `.try` blocks and their
|
||||
`catch`/`finally`/`fault`/`filter` handlers carry clause offsets; a `leave` that jumps out
|
||||
of a protected region is the tell that you are inside one.
|
||||
- An empty body, or a body that is only `ldnull; throw`, is a stub: the real code is elsewhere
|
||||
(a protector, a P/Invoke, a generated method).
|
||||
|
||||
### Instruction crib sheet
|
||||
|
||||
| CIL | C# it usually came from | What it buys you |
|
||||
|---|---|---|
|
||||
| `ldarg.0` then `ldfld` | `this.field` | instance state; the field name is a domain word |
|
||||
| `call` / `callvirt` | non-virtual call / virtual or interface dispatch | `callvirt` also carries the null check C# emits for `x.M()`; a `call` to an instance method is a base call or a compiler-chosen non-virtual call |
|
||||
| `newobj` / `initobj` | `new X(...)` / `default(T)` | allocation site; `initobj` on a local is struct zeroing |
|
||||
| `ldstr` | string literal | business vocabulary, error text, keys, URLs |
|
||||
| `ldc.i4.*`, `ldc.i8`, `ldc.r8` | numeric literal | thresholds, timeouts, retry counts |
|
||||
| `ldtoken` + `Type.GetTypeFromHandle` | `typeof(T)` | reflection, serialisation, DI registration |
|
||||
| `box` / `unbox.any` / `constrained.` | boxing, cast, generic call on a struct | interface dispatch through a type parameter |
|
||||
| `isinst` / `castclass` | `is`, `as`, `(T)` | type tests, pattern matching |
|
||||
| `switch` | dense integer `switch` | the jump table is in the instruction; a sparse switch becomes a comparison chain |
|
||||
| `brtrue`/`brfalse`, `beq`/`bne.un`, `bgt`/`blt`/`bge`/`ble` | `if`, `while`, `&&`, `\|\|`, comparisons | a gate is a branch whose two arms have different effects |
|
||||
| `leave`, `.try`, `catch`, `finally`, `fault`, `filter` | `try`/`catch`/`finally`, `using`, `lock`, `foreach` | the clause table, not the listing, holds the structure |
|
||||
| `dup` | a value used twice: object initialiser, null-conditional, assignment-as-expression | explains a stack dance a decompiler hid |
|
||||
| `ldftn` + `newobj ...::.ctor(object, native int)` | delegate creation: method group, lambda, event handler | the wiring from a surface to the logic |
|
||||
| `add_`/`remove_` + a delegate | `+=`/`-=` | event subscription, the usual path from a button to a gate |
|
||||
| `call ... GetEnumerator/MoveNext/get_Current` | `foreach` | iteration order matters for "last one wins" logic |
|
||||
| `Monitor.Enter`/`Exit` | `lock` | concurrency, and where a second instance is refused |
|
||||
| `callvirt ... Dispose` in a `finally` | `using` | resource lifetime |
|
||||
| `string::Concat`, `string::Format`, `AppendLiteral`+`AppendFormatted` | `+`, `string.Format`, interpolation | C# 10+ uses an interpolated-string handler, so interpolation looks like a builder, not a concat |
|
||||
| `Nullable<T>` `get_HasValue`, `GetValueOrDefault` | `T?`, `??`, `!= null` | optional configuration values |
|
||||
| `newarr`, `ldlen`, `ldelem`, `stelem` | array creation, `.Length`, indexing | table-driven logic |
|
||||
| `conv.i4`, `conv.u8`, `conv.r8` | numeric conversion | width and sign are where algorithm work actually breaks |
|
||||
| `throw` / `rethrow` | `throw;` | the message string names the failure and often the gate |
|
||||
| `ldsfld` / `stsfld` | static field | configuration, caches, singletons, global state |
|
||||
| `nop` | nothing | debug builds, and padding left by an obfuscator |
|
||||
|
||||
Two cautions on the crib sheet. First, the mapping is one direction only: `brtrue` is a branch,
|
||||
not necessarily an `if` -- it is equally a loop condition, a `&&` short-circuit, or a compiler
|
||||
null check. Second, CIL is a stack machine; the expression nesting the decompiler shows is its
|
||||
inference, and the instruction order is the fact.
|
||||
|
||||
### A decision, read in IL
|
||||
|
||||
The following is a constructed illustration, not a sample (`inferred`):
|
||||
|
||||
```
|
||||
IL_0000: call class App.Config App.Settings::get_Current()
|
||||
IL_0005: ldfld string App.Config::LicenseKey
|
||||
IL_000a: call bool [System.Runtime]System.String::IsNullOrEmpty(string)
|
||||
IL_000f: brtrue.s IL_0024
|
||||
...
|
||||
IL_0024: ldstr "No licence key found."
|
||||
IL_0029: call void [System.Windows.Forms]System.Windows.Forms.MessageBox::Show(string)
|
||||
```
|
||||
|
||||
That reads as `if (string.IsNullOrEmpty(Settings.Current.LicenseKey)) { MessageBox.Show("No licence
|
||||
key found."); ... }`. Four different kinds of claim came out of six instructions, and they must
|
||||
not be graded together:
|
||||
|
||||
- **Observed in the listing:** a static property `Settings.Current` is read, its `LicenseKey`
|
||||
field is tested for null-or-empty, and the true branch shows a message.
|
||||
- **Inferred:** the message is the refusal path for the licence feature, and this method is part of
|
||||
the gate.
|
||||
- **Unknown:** that the key is validated here rather than later; that `Settings.Current` reads a
|
||||
file, the registry, or a server response; that no second check exists (P22's neighbour: a
|
||||
decompiler showing one check is not a search for the others).
|
||||
|
||||
### What CIL does not tell you
|
||||
|
||||
- **Names.** Locals, parameters and often types are unnamed without a PDB; the decompiler's
|
||||
`num`, `text`, `flag` are its own.
|
||||
- **Inlining and dead code.** The JIT decides what runs, and the compiler already removed what
|
||||
could not run at compile time. A method present in metadata may never be called.
|
||||
- **Reflection and DI.** `Activator.CreateInstance`, `Type.GetType(string)`,
|
||||
`Assembly.Load`, `MethodInfo.Invoke`, and container registrations are calls that do not
|
||||
appear in the call graph. "No caller" is not "dead" in a framework application.
|
||||
- **The executed copy.** ReadyToRun and tiered compilation mean the bytes that ran may not be the
|
||||
CIL you read (`managed-dotnet.md`). When the loaded assembly is not the file on disk -- a
|
||||
single-file bundle's extracted copy, an assembly decrypted at start-up -- open the module from
|
||||
the running process rather than from the path: dotPeek's Process Explorer and dnSpyEx's modules
|
||||
window both do this (`observed`: dotPeek features page; dnSpyEx README).
|
||||
|
||||
## Compiler-generated names, and what they were
|
||||
|
||||
Roslyn leaves a consistent signature on the constructs it lowers. Recognising the name saves the
|
||||
minutes spent wondering why a method has a state machine in it.
|
||||
|
||||
| Shape | Origin | How to read it |
|
||||
|---|---|---|
|
||||
| `<M>d__3` as a struct, `IAsyncStateMachine` | `async` method | `MoveNext` is the body, split at each `await`; `<>1__state` selects the segment |
|
||||
| `<M>d__3` as a class, `IEnumerable`/`IEnumerator` | iterator | `MoveNext`/`Current`; each `yield` is a suspension point |
|
||||
| `<>c` | cached non-capturing lambda holder | the `b__N_M` methods are the lambdas |
|
||||
| `<>c__DisplayClassN_M` | closure | its fields are the captured variables; `b__N_M` is the lambda |
|
||||
| `<M>g__Local\|N_M` | local function | a helper the source declared inside a method |
|
||||
| `<>f__AnonymousType0` | anonymous type | the projection shape of a LINQ query |
|
||||
| `<PrivateImplementationDetails>` | array/struct initialiser blobs; string-switch hashing | `ComputeStringHash` means a `switch` on a string |
|
||||
| `<Module>` | module initialiser | runs before `Main`; a favourite place for a check |
|
||||
| `get_`/`set_`, `add_`/`remove_` | property and event accessors | |
|
||||
| `IFace.Method` | explicit interface implementation | |
|
||||
| `Program.<Main>$` | top-level statements | the real entry point |
|
||||
| `<Clone>$`, `PrintMembers`, `EqualityContract` | `record` | generated value semantics |
|
||||
|
||||
`inferred`: in Roslyn's async machines `<>1__state` starts at `-1` and `-2` marks completion,
|
||||
while an iterator's initial state is `-2`; each `await` or `yield` is a non-negative state. The
|
||||
convention is stable across compilers in practice but is not part of the language specification, so
|
||||
read the `switch` rather than trusting the numbers. Newer C# adds shapes (collection expressions,
|
||||
list patterns) that an older decompiler will render as raw IL; a construct that looks like a
|
||||
state machine but is not should be read as "this decompiler does not know this lowering yet".
|
||||
|
||||
dotPeek exposes the same information as a view instead of as a listing: its *show compiler-generated
|
||||
code* option renders lambdas, closures and auto-properties in their lowered form (`observed`:
|
||||
dotPeek features page). That is faster than reading IL when the question is "what did this lambda
|
||||
capture", and it is still a rendering -- the IL remains the authority.
|
||||
|
||||
## From method to business logic
|
||||
|
||||
A "logic map" is the deliverable, not a decompiled file. Build it in this order.
|
||||
|
||||
1. **Pin one observable behaviour** as a sentence someone else could test: "Importing a CSV with
|
||||
120 rows produces 120 records" or "A second copy of the app exits with a message". One
|
||||
behaviour at a time; a map of the whole program is a rewrite of the program.
|
||||
2. **Find the boundary that receives it.** The entry shape decides where to look:
|
||||
|
||||
| Shape | The hook to find |
|
||||
|---|---|
|
||||
| Console, service | `Main(string[])`, `ServiceBase.Run`, a top-level `Program.<Main>$` |
|
||||
| WinForms | `Application.Run(new F())`; the designer's `InitializeComponent` wires `Click +=` to a handler |
|
||||
| WPF / Avalonia | generated `App.Main`; `Click=`, `Command=`, and bindings; `INotifyPropertyChanged` names the state |
|
||||
| ASP.NET Core | `Program.Main` -> builder; controllers or `MapGet`; attributes carry the routes |
|
||||
| Unity | no `Main`; `MonoBehaviour` subclasses, `Awake/Start/Update`, code in `Assembly-CSharp.dll` |
|
||||
| Plugin host | types implementing a host interface, discovered by reflection: no static caller |
|
||||
|
||||
3. **Walk inward one hop at a time**, and at each hop write down the data the method receives. A
|
||||
hop that adds no data is a wrapper; skip it by following the only call it makes.
|
||||
4. **Stop at the first decision whose arms differ in effect.** Two arms that both call the same
|
||||
logger are not a business decision. A branch to a message, an exit, a different request, or a
|
||||
different file is.
|
||||
5. **Recover the data contract.** For each input the decision reads: where does it come from --
|
||||
argument, config file, registry, licence file, embedded resource, server response, clock? This
|
||||
is the part that turns "there is a check" into "the trial flag is a local file, and deleting it
|
||||
restores the trial".
|
||||
6. **Model the refusal path.** Denial is frequently not a crash: a message box, an exit code, a
|
||||
feature silently absent, a retry, a time bomb. Each is a different deliverable.
|
||||
7. **Write the rows.** One row per branch, with the condition in C# form and the evidence that
|
||||
produced it:
|
||||
|
||||
| # | Trigger | Input (source) | Condition | Effect | Evidence | Grade |
|
||||
|---|---|---|---|---|---|---|
|
||||
| 1 | app start | `LicenseKey` (config file) | `string.IsNullOrEmpty` | message, then exit | IL 0x06000012, IL_000f | observed |
|
||||
| 2 | "Export" clicked | `Rows` (grid) | `Rows.Count > 0` | writes CSV | handler token, string "/export" | inferred |
|
||||
|
||||
8. **Try to falsify row 1 and only row 1.** Re-read the branch in IL, set a breakpoint on it in
|
||||
dnSpyEx, and observe both arms with the original and a modified input. A map that has never had
|
||||
one row tested is a hypothesis with good formatting.
|
||||
|
||||
The seams where business logic hides, in the order they pay:
|
||||
|
||||
- **Strings.** Error text, config keys, registry paths, URLs, SQL, format strings. They survive
|
||||
renaming and they name the feature.
|
||||
- **Enums and constants.** A `Tier`, `Plan`, `Feature` enum with three values tells you the
|
||||
product's own model; `const int MaxFreeRows = 50` is a limit expressed as a number.
|
||||
- **Serialisation attributes.** `[JsonPropertyName]`, `[XmlElement]`, `[DataMember]` give the
|
||||
wire contract, which is the server's vocabulary and often the real model.
|
||||
- **Interfaces and base classes.** What a class implements says what role it plays even when the
|
||||
class is named `a`.
|
||||
- **Reflection and registration.** `AddSingleton<X>`, `services.AddTransient<...>`,
|
||||
`Assembly.GetTypes()` -- the composition root that names the participants.
|
||||
|
||||
## Recovering names from evidence
|
||||
|
||||
When the renamer won, names come from evidence, in this order of cost:
|
||||
|
||||
1. **A PDB.** Separate, embedded portable PDB, or a source-link reference. `ilspycmd --dump-pdb`
|
||||
shows what is there; `-usepdb` uses its local names. A mismatched PDB is worse than none: it
|
||||
produces confident wrong names.
|
||||
2. **Surviving metadata names.** Public API, interface members, explicit implementations, and
|
||||
attributes often keep their names even when private members do not.
|
||||
3. **Attribute arguments.** A `DllImport` target, a JSON property name, a route template, a
|
||||
command-line option: strings with meaning.
|
||||
4. **String literals and exception messages.** The domain vocabulary, verbatim.
|
||||
5. **Base types and interfaces.** Behaviour follows the role, not the name.
|
||||
6. **Shape.** Parameter and return types, arity, call sites, position between an input and an
|
||||
effect. A `bool`-returning method with one string parameter called immediately before a
|
||||
message box is a validator until proven otherwise.
|
||||
7. **Run time.** dnSpyEx locals and return values.
|
||||
|
||||
Rule: a name you assign is marked as yours, in the notes and in the logic map. Presenting a
|
||||
recovered name as the vendor's destroys the reader's ability to tell what came from the file.
|
||||
|
||||
## Verifying a reconstruction
|
||||
|
||||
A decompiled method is a hypothesis (P22). Verification is cheapest in this order, and each step
|
||||
can fail:
|
||||
|
||||
1. **Two renderings of the same body.** C# and IL. If they disagree, IL wins; if two decompilers
|
||||
disagree, neither has won -- the disagreement is the signal that the construct is being lowered
|
||||
in a way one of them does not model.
|
||||
2. **Round-trip.** `ildasm /out=x.il sample.dll`, `ilasm /dll x.il`, then run both. A difference
|
||||
in behaviour locates what you misread: header flags, assembly references, resources, attributes.
|
||||
`observed`: Microsoft Learn documents `/out=` for ildasm and `/dll` for ilasm.
|
||||
3. **One observed arm.** A breakpoint on the decision in dnSpyEx, with the operands watched, and
|
||||
the unmodified original run under the same conditions. A clean log is not an arm.
|
||||
4. **The claim's grade, restated.** "The IL contains a comparison against an empty string"
|
||||
(observed) is not "the licence is refused for an empty key" (inferred until an arm is seen) and
|
||||
is certainly not "this is the only check" (unknown).
|
||||
|
||||
For a deliverable that is a patch rather than an account, the authority is the original file and
|
||||
the verification is the one in `verification.md`: identity of what ran, which layer executed, and
|
||||
the feature observed directly.
|
||||
|
||||
## Where this hands over
|
||||
|
||||
| The reading reaches | Go to |
|
||||
|---|---|
|
||||
| Mixed-mode image, or a `DllImport` whose comparison matters | `static-analysis.md`, then `patching.md`; classify the layer first with `managed-dotnet.md` |
|
||||
| A single-file bundle whose payload is not on disk | `managed-dotnet.md`: extract, then re-triage what came out |
|
||||
| ReadyToRun output: IL present, native copy executing | `managed-dotnet.md`; do not patch CIL and assume it ran |
|
||||
| Native AOT output: no CIL to find | the native routes in `static-analysis.md` |
|
||||
| Obfuscated control flow, a dispatcher, a VM | `virtualization-and-flattening.md` |
|
||||
| The question is what the licence mechanism *is* | `license-mechanisms.md` |
|
||||
| The question is a live value, not a static one | `dynamic-debugging.md` (native) or dnSpyEx (managed) |
|
||||
|
||||
## What this file does not cover
|
||||
|
||||
`unknown`, and it is worth stating precisely: **no .NET tool was installed on the host that wrote
|
||||
this file**, so every command above is quoted from its project's or vendor's documentation and
|
||||
none was executed here. `observed` in this file therefore means "the named document says so",
|
||||
not "a run reproduced it". The versions behind the claims are the ILSpyCmd 11.0.0 help text, the
|
||||
Microsoft Learn pages for `ildasm` and `ilasm`, the de4dot README at the 2015-era source range,
|
||||
and the dnSpyEx README, read on 2026-10-24.
|
||||
|
||||
Also not covered:
|
||||
|
||||
- BAML/XAML semantics beyond extracting the resource (`--resource` decompiles BAML to XAML;
|
||||
reading the result as a UI specification is a separate exercise).
|
||||
- ReadyToRun IL editing and Native AOT symbol recovery.
|
||||
- Assembly resolution for a sample whose dependencies are absent, and multi-module assemblies.
|
||||
- Whether a given de4dot build reads a given modern assembly. That is a per-file measurement:
|
||||
run `-d`, then open the file, and record which of the two failed.
|
||||
- Whether dotPeek opens a given runtime build. That is a per-version fact; JustDecompile's support
|
||||
is frozen at its 2024 retirement, which is why it is not in the capability registry.
|
||||
- Any claim that a protector's output can be cleaned. "Unsupported obfuscator" is a statement
|
||||
about the tool's table, not about the target's strength.
|
||||
@@ -96,6 +96,10 @@ that has been exercised.
|
||||
| Managed-assembly patching | no managed sample was obtained; the toolchain is documented and its limitations are quoted from their own documentation |
|
||||
| Kernel driver analysis | no driver was analysed; the tooling is not installed on the development host |
|
||||
| Any claim about a specific commercial protector | the mechanism and the vendor's own documented descriptions are cited; nothing was measured against a protected sample |
|
||||
| Unity IL2CPP metadata recovery and registration repair | no Unity build was analysed here; the placements, the dumper's failure modes and the string-literal layer are taken from public write-ups |
|
||||
| Unpacking a packaged Python program | no packaged sample was analysed here; the container behaviour is documented by the packagers' own tooling |
|
||||
| Recovering code objects from a versioned wrapper | no wrapped sample was obtained; the mechanism is quoted from one public analysis and is version-specific |
|
||||
| Instruction-level reading of a listing | no target was disassembled here; the conventions are documented architecture, and a producer claim (compiled here, assembled there) is `inferred` until a build whose toolchain is known confirms it |
|
||||
|
||||
## Where the corpus comes from
|
||||
|
||||
|
||||
@@ -95,6 +95,10 @@ Tooling this repository's host probe looks for, and what each is for:
|
||||
- No decompiler is required to locate behaviour, but a name-preserving disassembly is much
|
||||
faster than reading token numbers by hand.
|
||||
|
||||
Which of these to use for which question, how to read a CIL listing, and how to go from a method
|
||||
body to a statement about business logic is `dotnet-decompilation.md`. This file stops at
|
||||
classification and at the structural rules for an edit.
|
||||
|
||||
Cheap questions that answer a lot before any editing: is the assembly signed with a strong
|
||||
name, does it carry a mixed-mode native part, does it reference a licensing or activation
|
||||
assembly, and are the type and method names meaningful or renamed to unusable characters.
|
||||
|
||||
@@ -12,7 +12,7 @@ That is the shape worth fearing. A crash announces itself; these do not.
|
||||
|
||||
Each entry states the failure, the mechanism that makes it invisible, and the check that catches it.
|
||||
|
||||
P1-P25 are format and mechanism failures of Windows binaries; P26-P34 are failures of the *analysis*
|
||||
P1-P25 are format and mechanism failures of Windows binaries; P26-P37 are failures of the *analysis*
|
||||
itself — sampling read as observation, a self-built parser trusted, a verification that could not have
|
||||
failed. Those are written with Windows examples because that is where they were paid for, but the
|
||||
mechanism does not depend on the platform: read them on a managed assembly and a driver the same way.
|
||||
@@ -348,3 +348,51 @@ succeeds against a different target. PowerShell adds its own layer (argument re-
|
||||
*Check:* when an argument-heavy command fails in a way that does not match its own parser, reproduce
|
||||
it with the argument written to a file or passed as an array, and print the argv the child actually
|
||||
received before changing the command.
|
||||
|
||||
**P35. A decrypted buffer that parses, treated as the buffer the process used.**
|
||||
|
||||
A buffer taken from memory is not a file that was read from disk. Loaders patch headers in place:
|
||||
the magic and the version field can read as zero after the loader has consumed them, and the length
|
||||
is not stored anywhere the file itself would carry it. A dump taken from the mapped view's size, the
|
||||
allocation's size, or a constant therefore has a correct-looking header and a truncated or padded
|
||||
tail, and the tool that consumes it reports a table read past its end, a count that disagrees with a
|
||||
neighbouring table, or a parse that succeeds with nonsense after the truncation point.
|
||||
|
||||
*Check:* compute the length from the buffer's own structure — for a metadata-style header, the last
|
||||
`(offset, count)` pair with a non-zero count bounds it — and cross-check the result against one
|
||||
independent field (the largest `offset + count`, or a string table's declared end). Record the
|
||||
header fields before and after restoring the ones the loader cleared. A dump that parses is a dump
|
||||
that parsed; only the record of what it was taken from and what was restored makes it the buffer
|
||||
the process used.
|
||||
|
||||
**P36. The version the file declares, believed over the structure that parses.**
|
||||
|
||||
A container, a metadata file or a code-object stream carries a version field, and a tool that reads
|
||||
it selects a layout. After a custom build, a spliced layout or a hand-modified header, the field and
|
||||
the layout can disagree — a version-31 header over a version-29 struct, one extra 32-bit field
|
||||
shifting every following pointer by four bytes. The tool then reports a successful parse whose
|
||||
records point four bytes off, which surfaces as method bodies that belong to other methods, names
|
||||
attached to the wrong metadata, or a decompiler that produces something almost readable.
|
||||
|
||||
*Check:* when a version-sensitive parse produces records that are *plausible but misaligned*, parse
|
||||
the same bytes under the neighbouring layout and compare which one yields pointers that land inside
|
||||
the section they claim and counts that match their tables. A version field is a claim by the file;
|
||||
the structure that produces consistent cross-references is the one that is executing, and the
|
||||
disagreement itself is the finding to record.
|
||||
|
||||
**P37. The 32-bit view searched as though it were the only view.**
|
||||
|
||||
A 32-bit target on a 64-bit host does not read the paths its own code names. WOW64 redirects
|
||||
`HKLM\SOFTWARE\Vendor` to `HKLM\SOFTWARE\Wow6432Node\Vendor` and `System32\` to `SysWOW64`, and both
|
||||
redirections are silent: every call succeeds, every path exists, and the default tools show the
|
||||
native view. A search of the native path therefore returns nothing, and the conclusion drawn from it
|
||||
— "the target keeps no local configuration, so the decision must be remote" — is wrong in a way that
|
||||
redirects the entire investigation to a layer that may not own the decision at all. A write that
|
||||
"succeeded" can likewise land in a per-user virtual store when the process is unmanifested and not
|
||||
elevated, so the setting is not in the key the code names either.
|
||||
|
||||
*Check:* establish the process bitness from the process, not from the image header
|
||||
(`IsWow64Process2`), then search both the native key and its `Wow6432Node` twin, and both the
|
||||
`System32` and `SysWOW64` copies of the file. Record which view was searched next to the negative
|
||||
result. "Not found" is a statement about one view; only both views together make it a statement
|
||||
about the machine.
|
||||
|
||||
@@ -0,0 +1,179 @@
|
||||
# Python-packaged Windows software
|
||||
|
||||
Goal: recognise a Python program that has been packaged into an executable, find the layer that
|
||||
holds the logic, and separate three problems that look alike at first contact — a **packed
|
||||
archive**, a **cryptographic code-object wrapper**, and **native-compiled Python**.
|
||||
|
||||
## When to load this
|
||||
|
||||
Load this when the target directory holds `python3xx.dll` (or `python27.dll`), a
|
||||
`_internal/` tree, `base_library.zip`, a `PYZ` archive or a `pyarmor_runtime` module; when the
|
||||
executable shows a "failed to execute script" dialog; when strings contain `PyInstaller`,
|
||||
`pyi-`, `pyiboot` or `pyarmor`; or when a decompiled module is high-entropy while the rest of the
|
||||
program is ordinary Python.
|
||||
|
||||
The layer decides the route:
|
||||
|
||||
| What is there | What it is | Where to go |
|
||||
|---|---|---|
|
||||
| a packaged archive with ordinary bytecode inside | a packager: the program is normal Python with a container around it | this file, "Unpacking the archive" |
|
||||
| bytecode that is encrypted per code object, with a small runtime module beside it | a code-object wrapper (PyArmor is the one described here) | this file, "The wrapper layer" |
|
||||
| `python3xx.dll` present but no bytecode to find | native-compiled Python: the logic was translated to C and built | this file, "Native-compiled Python", then the native routes |
|
||||
| a native extension (`.pyd`) that is itself protected | a protector on top of native code | `references/virtualization-and-flattening.md` or `references/protectors-and-packers.md` |
|
||||
|
||||
Grades: the file-layout facts are `inferred` from the tools' documented behaviour; the wrapper
|
||||
internals below are `unverified` here, taken from a public write-up and not reproduced on a
|
||||
sample. Each section says what would make its rows `observed`.
|
||||
|
||||
## The gate that decides everything: the Python version
|
||||
|
||||
A `.pyc` is a version-specific serialisation (`marshal`) of a code object. The header carries a
|
||||
magic number, and the body's field order changed several times across 1.x-3.13. **A code object
|
||||
parsed under the wrong version yields a plausible wrong result rather than an error**, which makes
|
||||
this the most expensive fact to get wrong and the cheapest to establish.
|
||||
|
||||
Read it before anything else, from the least ambiguous source available:
|
||||
|
||||
| Source | What it gives |
|
||||
|---|---|
|
||||
| the runtime DLL's name (`python311.dll`) | the major and minor version, when the packager kept the standard name |
|
||||
| the DLL's version resource | the full version, including the patch level the packager bundled |
|
||||
| `sys.version` in the bundled library, if a `.py` or a string constant survives | the exact build string |
|
||||
| the code object's magic number | the marshalling version, once you can read four bytes |
|
||||
|
||||
Record the version next to the artifact's hash. Every later step — unmarshalling, decompiling,
|
||||
re-importing — is only valid under the version that produced the bytes.
|
||||
|
||||
## Layer map
|
||||
|
||||
| Layer | What it holds | What it costs to remove |
|
||||
|---|---|---|
|
||||
| the packager's bootloader | unpacks the archive to a temporary directory and runs the entry script | nothing: it is a documented container, and the payload lands on disk |
|
||||
| the archive | compressed entries: the bytecode modules, data files, extension modules | extraction only |
|
||||
| the code objects | the program's logic, as `marshal` data | a version-matched unmarshaller and a decompiler |
|
||||
| the wrapper (if present) | encrypted code objects and literals, plus a runtime that decrypts them per module | the key derivation, or a dump after decryption |
|
||||
| native extensions | C/C++ modules the program imports | the ordinary native route; a protector here is a separate problem |
|
||||
|
||||
## Unpacking the archive
|
||||
|
||||
**Diagnosis before extraction.** The packager leaves fingerprints that are cheap to read: the
|
||||
runtime DLL, the archive file or a `base_library.zip`, the `_internal` directory convention, and
|
||||
the bootloader's own strings. `scripts/pe_triage.py` plus a directory listing answers which
|
||||
packager it is; the packager's extraction tool is then a known one instead of a guess.
|
||||
|
||||
**Extraction.** Two options, and the second is the one that survives a modified archive:
|
||||
|
||||
1. Run the packager's own extractor against the executable. It reads the container format
|
||||
directly and needs no execution of the target. The result is a directory of modules.
|
||||
2. Run the target once in an isolated environment with its temporary directory redirected and
|
||||
captured. This sees the payload the process actually used, which is the control for option 1:
|
||||
if the two differ, the on-disk archive is not the one being executed.
|
||||
|
||||
**Then unmarshal and decompile under the recorded version.** Two checks keep this honest:
|
||||
|
||||
- the module count and the import graph should look like a program (an entry module that imports
|
||||
tens of modules), not like a fragment;
|
||||
- a decompiled module must contain calls whose names appear in the archive's string data. A
|
||||
decompiler run under the wrong version fails this test while still producing output.
|
||||
|
||||
## The wrapper layer
|
||||
|
||||
In the version analysed, the wrapper does not transform control flow; it encrypts the artifacts the
|
||||
interpreter needs and decrypts them as they are loaded. That distinction is what makes it tractable,
|
||||
and it is also why "deobfuscation" is the wrong word for the work: there is no obfuscated logic to
|
||||
simplify, only a key to find or a plaintext to capture. The same analysis warns that the scheme has
|
||||
no obfuscation layer to fall back on, which is why wrapping is usually accompanied by native
|
||||
compilation or by a protector on the runtime module.
|
||||
|
||||
The following is what one public analysis reported for one version (`unverified`; none of it was
|
||||
reproduced here). Treat the field names as the shape to look for rather than as offsets to trust.
|
||||
|
||||
| Element | Reported mechanism |
|
||||
|---|---|
|
||||
| the marker in the code object | a `co_flags` bit (`0x20000000`) says "this code object carries wrapper data". When it is clear, the object is ordinary bytecode |
|
||||
| the extra data | after the standard fields, a length-prefixed blob, with counts packed into its first byte for per-function records and code descriptors |
|
||||
| the descriptor | stored as a constant in the code object, referenced by index; its first 8 bytes are a placeholder rewritten at run time, the rest is `flags`, a start index and a length |
|
||||
| descriptor flags | bit `0x2` short form, `0x4` "the nonce is XORed with a key", `0x8` "copy the prologue back after decryption" |
|
||||
| the cipher | AES in CTR mode. The key is 16 bytes derived by MD5; the nonce is 12 bytes cut from the encrypted region itself, with the final byte set to `2` |
|
||||
| the key derivation | MD5 over: a versioned identifier string (`pyarmor-vax-<6 digits>`; all zeros for one edition), a fixed-length slice of a key blob, a second slice whose length comes from a field in its own header, and a 16-byte value XORed with a constant |
|
||||
| the nonce for literals | the first 12 bytes of the second key slice; in the analysed build the ASCII text `i.non-profit` |
|
||||
| an optional second transform | when a "xor key procedure" length is non-zero, a small bytecode interpreter computes a 12-byte key that is XORed into the nonce before decryption |
|
||||
| the mini interpreter | 8 registers, 11 opcodes: add/subtract/multiply/divide/XOR/assign against the register named by the high nibble, plus store operations at fixed offsets of a 12-byte output |
|
||||
| the prologue copy | the first `N` bytes of the decrypted region are copied to offset zero and the source is overwritten with NOPs, because the interpreter expects the prologue at the front |
|
||||
|
||||
**Two routes, and what each buys.**
|
||||
|
||||
- **Static.** Reproduce the key derivation, decrypt each descriptor's range, restore the prologue,
|
||||
and the code object becomes ordinary bytecode. The published tooling for this is version-matched
|
||||
to the wrapper's version, and the version check is part of the tool's correctness rather than a
|
||||
formality: an object decrypted under the wrong scheme produces bytes that unmarshal into
|
||||
nonsense, or worse, into a plausible object with corrupted constants.
|
||||
- **Dynamic.** The interpreter decrypts a module just before executing it, so a dump taken at the
|
||||
right moment contains plaintext. The published analysis reported this as **incomplete**: the
|
||||
decryption is per node and per literal, so a single snapshot does not reconstruct the whole
|
||||
program. It is the cheaper route for "what does this one function do" and the wrong route for
|
||||
"reconstruct the package".
|
||||
|
||||
**The tempting wrong move**, worth naming because it produces a working-looking result: patching
|
||||
the wrapper's check or skipping the decrypt call. The module then either runs with a corrupt code
|
||||
object or falls back to a path that never touches the protected logic, and the session ends with a
|
||||
program that starts and does nothing.
|
||||
|
||||
## Native-compiled Python
|
||||
|
||||
When the logic is in a `.pyd` or in a compiled executable with no bytecode to find, the program
|
||||
was translated to C and built (Nuitka and Cython are the common ones; hand-written bindings are
|
||||
another). The ordinary native workflow applies from that point: the module is a PE with the
|
||||
Microsoft C++ runtime, its structure is readable by `scripts/pe_triage.py`, and the Python C-API
|
||||
calls are visible imports that mark the boundary between compiled Python and the interpreter.
|
||||
|
||||
Two consequences:
|
||||
|
||||
- **The Python version is still a fact you need**, because the C-API symbols the module imports are
|
||||
version-specific, and a module built for 3.11 does not load into 3.12.
|
||||
- **A protector on a `.pyd` is a native-protector problem**, and the protections that matter there
|
||||
are the ones in `references/virtualization-and-flattening.md`. A wrapper has no relevance to
|
||||
code that never becomes a code object.
|
||||
|
||||
## Verification
|
||||
|
||||
| Claim | The check that settles it |
|
||||
|---|---|
|
||||
| the payload came from this executable | hash the binary, hash the extracted module, and run the target once with the temporary directory captured; the two payloads must match |
|
||||
| the decompiled module is the module that ran | import it under the recorded interpreter and observe the same behaviour on the same input as the packed original. A decompiler's output that does not import has proved nothing |
|
||||
| the Python version is right | recompile a decompiled module with that interpreter and compare the code object's structure (arg counts, names, constants) with the original |
|
||||
| the wrapper was removed rather than bypassed | the recovered module imports with no wrapper runtime present, and every function in it executes. A module that only works while the wrapper's runtime is loaded is a hook, not a recovery |
|
||||
|
||||
Record the interpreter version, the artifact hashes and the command in the result. "It decompiled"
|
||||
is a statement about the decompiler.
|
||||
|
||||
## What this route does not do
|
||||
|
||||
- **Ship a general unpacker.** The wrapper's format is version-specific, and the published tools
|
||||
state which versions they cover; a version outside that set is a research task, not a command.
|
||||
- **Recover a key that is bound to a licence.** Where the key material is delivered by an
|
||||
activation step, the bound value lives in the same category as
|
||||
`references/network-activated-licensing.md` describes, and the client-side file is not where
|
||||
the decision is made.
|
||||
- **Treat recovered source as the original.** Decompiled Python is a reconstruction; names of
|
||||
locals and the shape of expressions are not what the author wrote.
|
||||
- **Cover Python packaged for another platform.** An Android or iOS bundle is a different artifact
|
||||
class; `references/handoff-boundaries.md` names the owner.
|
||||
|
||||
## What makes this `observed`
|
||||
|
||||
- the packager identified from the files, with the paths and the hashes;
|
||||
- the interpreter version and where it was read from;
|
||||
- the extraction route used, and the control run that shows the extracted payload is the executed
|
||||
one;
|
||||
- for the wrapper: the descriptor, the derivation reproduced, one decrypted object that unmarshals
|
||||
and imports, and the literal sample that decodes to text a program would contain;
|
||||
- one module that was recovered and executed with the wrapper absent.
|
||||
|
||||
## Provenance of the unverified rows
|
||||
|
||||
The wrapper analysis summarised above comes from a public write-up built on two open-source
|
||||
projects, `Pyarmor-Static-Unpack-1shot` and `Pyarmor-Tooling`; the mechanisms are theirs, the
|
||||
paraphrase is this file's, and neither project was run against a sample here. The packager
|
||||
behaviour is documented by the packagers' own tooling. When one of these rows is tested, the
|
||||
result belongs beside the artifact's hash and the wrapper's version, not in this section.
|
||||
@@ -36,6 +36,12 @@ without a check.
|
||||
| Your signature-based patch worked on one version and misses on the next | `references/aob-and-signatures.md` |
|
||||
| Two supposedly identical builds behave differently | `references/pe-diff-and-versions.md` |
|
||||
| The target is a .NET assembly and hex-patching it does nothing | `references/managed-dotnet.md` |
|
||||
| A .NET assembly decompiles, but the names are gone or the C# does not add up | `references/dotnet-decompilation.md` |
|
||||
| A Unity game's `global-metadata.dat` is missing, empty or unreadable beside its `GameAssembly.dll` | `references/unity-il2cpp.md` |
|
||||
| il2cppdumper reports `CodeRegistration : 0`, or the metadata version disagrees with the struct it parses | `references/unity-il2cpp.md` |
|
||||
| A hot-update assembly decompiles to high-entropy IL, or an AssetBundle refuses to open | `references/unity-il2cpp.md` |
|
||||
| The target directory holds `python3xx.dll`, `_internal` or `pyarmor_runtime` | `references/python-runtime-bundles.md` |
|
||||
| A Python module is high-entropy while the rest of the packaged program is ordinary | `references/python-runtime-bundles.md` |
|
||||
| The payload holds a large `data/app.so` and hardly any native code | `references/flutter-and-dart-aot.md` |
|
||||
| The sample is an installer, and the interesting binary is nowhere on disk after install | `references/installers-and-packaging.md` |
|
||||
| The file is a driver, or it refuses to load without a driver present | `references/kernel-and-drivers.md` |
|
||||
@@ -46,6 +52,9 @@ without a check.
|
||||
| A tool returns more output than you can read, or the same run returns different amounts | `references/toolchain.md` |
|
||||
| The binary was produced by a compiler you have not identified | `references/compiler-fingerprints.md` |
|
||||
| The target is written in Go, Rust or Delphi and the call structure looks wrong | `references/compiler-fingerprints.md` |
|
||||
| A detour or code cave crashes its callee, or the arguments arrive at wrong offsets | `references/assembly-idioms.md` |
|
||||
| A 32-bit target's licence file or registry key is absent from the path the documentation gives | `references/assembly-idioms.md` |
|
||||
| A prologue does not look like the compiler the headers named | `references/assembly-idioms.md` |
|
||||
| You are about to conclude "it must be server-side" | `references/network-activated-licensing.md` |
|
||||
| You cannot tell whether a failure is your patch or the target's own behaviour | `references/verification.md` |
|
||||
| You are about to write off a route as impossible | `references/protectors-and-packers.md` |
|
||||
@@ -67,6 +76,7 @@ reference that is loaded at the wrong moment costs context and answers nothing.
|
||||
| `references/pe-structure.md` | a header, section, import, relocation, TLS or checksum question — or when an offset and an RVA disagree |
|
||||
| `references/static-analysis.md` | reading code: disassembly, decompilation, structure recovery, and where a listing lies |
|
||||
| `references/compiler-fingerprints.md` | the toolchain is unidentified, or the call structure does not look like C or C++ |
|
||||
| `references/assembly-idioms.md` | a listing must be read at the instruction level: the convention moves the arguments, the prologue says who produced the code, a string instruction stands in for a library routine, or a detour must preserve the frame |
|
||||
| `references/pe-diff-and-versions.md` | two builds must be compared, or a finding has to survive a version change |
|
||||
| `references/patching.md` | any byte edit: site choice, equal-length discipline, checksum, and proving the patch is reached |
|
||||
| `references/aob-and-signatures.md` | a patch must be located across versions rather than at one address |
|
||||
@@ -82,6 +92,9 @@ reference that is loaded at the wrong moment costs context and answers nothing.
|
||||
| `references/virtualization-and-flattening.md` | the code is readable but its shape is wrong: dispatchers, opaque predicates, virtual machines |
|
||||
| `references/symbolic-execution.md` | reading has stopped paying: when a solver or an emulator is the cheaper route |
|
||||
| `references/managed-dotnet.md` | a managed assembly, or a mixed-mode one, is the target |
|
||||
| `references/dotnet-decompilation.md` | a managed assembly must be read rather than classified: deobfuscation, decompiler choice, CIL reading, and the path from a method body to a business rule |
|
||||
| `references/unity-il2cpp.md` | a Unity IL2CPP build: the metadata file is missing or protected, the dumper will not find its registrations, or the hot-update and bundle layers must be read |
|
||||
| `references/python-runtime-bundles.md` | a packaged Python program: which packager produced it, the interpreter version it needs, the wrapper around its code objects, or Python compiled to native code |
|
||||
| `references/installers-and-packaging.md` | the sample arrives as an installer or a package |
|
||||
| `references/flutter-and-dart-aot.md` | the payload is a Flutter application: an ELF `app.so` inside a Windows package, with the behaviour in compiled Dart |
|
||||
| `references/kernel-and-drivers.md` | the boundary where user-mode tooling stops |
|
||||
|
||||
@@ -0,0 +1,244 @@
|
||||
# Unity IL2CPP - the metadata layer
|
||||
|
||||
Goal: decide which layer of a Unity build owns the behaviour, get a usable
|
||||
`global-metadata.dat` when the one on disk is absent or unreadable, and know which of the
|
||||
remaining layers (registrations, string literals, hot-update assemblies, AssetBundles) still has
|
||||
to be fixed before any name in the dump means anything.
|
||||
|
||||
## When to load this
|
||||
|
||||
Load this when the target ships `GameAssembly.dll` beside `UnityPlayer.dll`, when
|
||||
`global-metadata.dat` is absent, zero bytes, high-entropy or refuses to parse, when
|
||||
il2cppdumper reports `CodeRegistration : 0` or a version that disagrees with the struct it then
|
||||
parses, when a hot-update assembly decompiles to high-entropy IL, or when an AssetBundle refuses
|
||||
to open with its version string intact.
|
||||
|
||||
Two adjacent routes: a **Mono** Unity build carries `Data/Managed/Assembly-CSharp.dll` and is a
|
||||
managed-assembly problem, so read `references/managed-dotnet.md` first; an Android or ELF build
|
||||
is another discipline's artifact, and `references/handoff-boundaries.md` says whose.
|
||||
|
||||
Everything in this file is graded. The mechanisms are `inferred` from il2cpp's own structure and
|
||||
from the source of the tools named. The per-build observations come from public write-ups and are
|
||||
`unverified` here: they were not reproduced on a sample in this repository. Each section ends
|
||||
with what would move its rows to `observed`.
|
||||
|
||||
## The files, and what each one is for
|
||||
|
||||
| File | What it holds | What it is for analysis |
|
||||
|---|---|---|
|
||||
| `GameAssembly.dll` | the IL, translated to C++ and compiled ahead of time | the code. This is a normal PE for the native routes, with the caveat that almost nothing is a hand-written function |
|
||||
| `global-metadata.dat` | type, method, field and parameter names; string literals; the tables that address the code | the names. Without it a dump is thousands of anonymous functions |
|
||||
| `UnityPlayer.dll` | engine: archive storage, AssetBundle loading, the player loop | where container formats are parsed, and where a modified container shows up |
|
||||
| `Data/Managed/*.dll` | managed assemblies | present in **Mono** builds. In an IL2CPP build they are absent unless a hot-update scheme ships them |
|
||||
| `data.unity3d`, `*.bundle`, `StreamingAssets` | content: scenes, assets, bundles | the data layer. A licence value rendered from a bundle is data, not code |
|
||||
| `UnityCrashHandler64.exe` | crash reporter | noise for this route. Its presence is a build-fact, not a lead |
|
||||
|
||||
The consequence that decides the plan: **patching code and reading names are two different
|
||||
operations on two different files.** A PE edit to `GameAssembly.dll` can change a branch, and it
|
||||
will not restore a single method name; a repaired metadata file makes everything readable and
|
||||
changes no behaviour.
|
||||
|
||||
## First question: Mono or IL2CPP
|
||||
|
||||
| What is on disk | Variant | Where to go |
|
||||
|---|---|---|
|
||||
| `GameAssembly.dll` and `global-metadata.dat` | IL2CPP | this file |
|
||||
| `Data/Managed/Assembly-CSharp.dll`, `MonoBleedingEdge/` | Mono | `references/managed-dotnet.md` |
|
||||
| `GameAssembly.dll`, no metadata file, or a 0-byte one | IL2CPP with the metadata produced at run time | this file, "Where the metadata is" |
|
||||
| neither, but `UnityPlayer.dll` and a `Data/` tree | a runtime build whose scripting backend needs identifying | `references/compiler-fingerprints.md`, then this file |
|
||||
|
||||
## Where the metadata is, and what each variant costs
|
||||
|
||||
Six placements were reported across the write-ups read for this file. The first column is what
|
||||
you see, and it is the only part that generalises; the rest is `unverified` per build.
|
||||
|
||||
| What is on disk | What was reported | Route |
|
||||
|---|---|---|
|
||||
| A plain file starting `AF 1B B1 FA` | the ordinary case. Bytes 4-8 carry the metadata version | read it. Nothing to decrypt |
|
||||
| A file with the magic intact and an unreadable body | encryption applied to the body only, magic left as a marker. In one case the loader returned the decrypted buffer from a routine reached from `il2cpp::vm::MetadataCache::Initialize`; the file handle was opened with `CreateFileW` and the returned view was the plaintext | dump the returned view from memory, or recover the key from the routine |
|
||||
| A file with a different magic, e.g. `0x1357FEDA` | a private container: a fixed header, a `0x40`-byte program, then data in `0x40`-byte blocks passed through a 255-case bytecode VM. The decrypted block began with an 8-byte sentinel (`"CODEPHIL"`) and the plaintext metadata followed it | either reimplement the VM from its opcode handler, or dump the plaintext buffer after the loader ran. The second is cheaper and answers the same question |
|
||||
| No file, and a `GameAssembly.dll` whose metadata loader jumps into a protector section | the container is the protection: the loader was redirected into a section holding both the ciphertext and the VM that decrypts it. In that build the decrypt sat at `il2cpp::vm::MetadataLoader::LoadMetadataFile`'s return, and the decrypted start address was stored in a global | dump the pointer after the call. Do not start by reading the VM |
|
||||
| The metadata carried as a **PE resource** of `GameAssembly.dll` | resource type a fixed name, resource **name** a 64-bit hash of the logical file name, and the blob encrypted (XXTEA in that build) | walk the resource tree, reproduce the name hash, decrypt. All of it is offline |
|
||||
| Embedded in the code module with no resource entry | the metadata was compiled into the binary and its pointer computed at load | locate the pointer, not the file. The file-based tools will keep reporting "missing" |
|
||||
|
||||
The resource variant is the one worth doing statically, because it needs no running target. The
|
||||
name hash in that build was two accumulators over the ASCII name, one FNV-1a style
|
||||
(`h = h * 0x1000193 ^ byte`) and one multiply-add (`r = r * 0x83 + byte`), concatenated into one
|
||||
64-bit value and compared against a constant; the resource id was then a small integer selected by
|
||||
that comparison. That is a per-build detail, and the transferable part is the shape: **a fixed
|
||||
logical name hashed into a resource name is a resource lookup, not a file lookup.**
|
||||
|
||||
What would move these rows to `observed`: one build of each placement, with the bytes, the
|
||||
routine and the resulting file digest recorded.
|
||||
|
||||
## The decrypt site is one level above the loader
|
||||
|
||||
The single most expensive mistake on this route, reported three separate ways, is assuming the
|
||||
decryption lives in `il2cpp::vm::MetadataLoader::LoadMetadataFile` because that is the function
|
||||
named for loading.
|
||||
|
||||
| Reported arrangement | What it means for the search |
|
||||
|---|---|
|
||||
| the loader was byte-identical to upstream; the added call was in `il2cpp::vm::GlobalMetadata::Initialize` | diffing the loader against upstream returns nothing and looks like "no decryption here" |
|
||||
| the loader was unchanged, and the decrypted buffer came back from the file-open path | the decrypt is a call inside the reader, not a wrapper around it |
|
||||
| `MetadataHash::Initialize`-style paths produced the same effect from a different call site | the entry point varies by Unity version and by how the build was modified |
|
||||
|
||||
The search that works is over **data flow, not names**: find where the global metadata pointer
|
||||
(il2cpp keeps one) is written, then read backwards. Whether the build still exports the il2cpp API
|
||||
(`il2cpp_*` names in the export table) is a per-build measurement, and it is worth taking before
|
||||
reading a listing: `scripts/peutil.py` reports the export table in one pass, and where those names
|
||||
survive they identify the layer for free.
|
||||
|
||||
## Dumping the plaintext buffer
|
||||
|
||||
The pattern below is the one to reuse. It is reported, not reproduced here (`unverified`), and
|
||||
every step is checkable by the person running it.
|
||||
|
||||
1. **Reach the buffer.** Break (or hook) at the return of the routine that produced it, or on the
|
||||
instruction that stores the metadata pointer. The value is a pointer to the plaintext, not to
|
||||
the file.
|
||||
2. **Compute the length; do not guess it.** The metadata header is a run of `(offset, count)`
|
||||
pairs of 32-bit values beginning at `0x08`, and the last pair with a non-zero count gives the
|
||||
end of the file.
|
||||
The reported walk goes **backwards from `0x10C`** in steps of 8, takes the first pair whose
|
||||
count is non-zero, and returns `offset + count`:
|
||||
|
||||
```
|
||||
i = 0x10C
|
||||
while i > 0:
|
||||
count = u32(header + i)
|
||||
if count != 0:
|
||||
offset = u32(header + i - 4)
|
||||
return offset + count
|
||||
i -= 8
|
||||
```
|
||||
|
||||
A length taken from the file size, from the mapped view size or from a constant produces a
|
||||
buffer with a plausible header and a truncated tail, and the failure appears later as a table
|
||||
read past its end. Cross-check the computed length against at least one of: the largest
|
||||
`(offset + count)`, a Unicode string at `stringLiteralDataOffset`, or the count the tool
|
||||
reports for a related table.
|
||||
3. **Write it out and restore the header.** Memory dumps were reported with the magic and the
|
||||
version field zeroed, because the loader patches them in place. Restoring `AF 1B B1 FA` and the
|
||||
correct version is part of the dump, not an optional repair: a tool that reads the version from
|
||||
a zero field will parse the body with the wrong structure and produce a plausible, wrong dump.
|
||||
4. **Keep a control.** Hash the original file (or record that there was none), hash the dump, and
|
||||
keep both. A dump that parses is not a dump that matches what the process used.
|
||||
|
||||
## The second layer: string literals
|
||||
|
||||
A metadata file can decrypt cleanly and still hold garbage names, because the string literals have
|
||||
their own encryption. Reported mechanisms:
|
||||
|
||||
| Mechanism | How it was identified | How it was undone |
|
||||
|---|---|---|
|
||||
| a per-literal transformation applied when a literal is interned | the decode funnel is `il2cpp::vm::String::NewLen`; everything goes through it | hook it, convert the returned UTF-16LE back to UTF-8, patch the metadata in place |
|
||||
| a length-keyed byte XOR | the routine was called per literal with the length in hand; the key reduced to `len ^ 0x2E` | implement the reduction (the XOR is applied uniformly to all bytes) |
|
||||
| literals readable but names not | the name tables are not encrypted and only the literal blob is | fix only the literal blob |
|
||||
|
||||
The verification is a sample, not a count: pick ten literals, decode them, and check that each is
|
||||
text a program would contain — a format string, a menu label, a URL. A decryption that produces
|
||||
ASCII-looking noise passes a length check and fails this one.
|
||||
|
||||
## The third layer: registrations, and why il2cppdumper gives up
|
||||
|
||||
il2cppdumper's automatic mode searches for two registration structures by shape. When the build is
|
||||
modified the search fails in ways that each look like a different problem.
|
||||
|
||||
| Symptom | Mechanism | What was done |
|
||||
|---|---|---|
|
||||
| `CodeRegistration : 0`, `No symbol is detected`, "try manual mode" | the heuristic scans for arrays of pointers into the code section; a metadata or code layout it does not expect leaves it with no candidate | manual mode: locate the registration by following the il2cpp initialisation path, then enter the address |
|
||||
| a candidate found, but the reported address is wrong | the heuristic matched a different pointer array that has the same shape | enter the address found by following the code that consumes the registration |
|
||||
| "Metadata Version: 31", but the registration struct is the version-29 layout | the metadata version field says one thing and the code was built with another; the 31 struct adds fields the build does not have | set the metadata version to 29 (restore the field), or teach the dumper the layout that is actually there |
|
||||
| the dumper classifies the build as `29.1` | a heuristic over the generic-method pointer count, which a large build inflates | force the version explicitly |
|
||||
| `methodDef` offsets land `+0x20` / `+0x24` away | a 29-layout registration spliced under a 31 header, so one extra 32-bit field shifts every following pointer | shift the field offsets in the dumper's struct, not the data |
|
||||
| auto and manual both fail | the code section itself is protected, so no registration can be read at rest | dump the whole code module from memory, then apply the ordinary dump-repair route in `references/memory-and-dumps.md` |
|
||||
|
||||
Two rules survive all six rows. **A version string is a claim by the file, not by the code** —
|
||||
when the struct disagrees with it, the struct is what executes. And **the dumper's output is a
|
||||
reconstruction**: names come from the metadata, addresses from the code, and a mismatch between
|
||||
them produces a dump that decompiles into functions with the wrong bodies.
|
||||
|
||||
## Hot-update assemblies
|
||||
|
||||
A Unity IL2CPP game can add managed code at run time through an IL interpreter (HybridCLR is the
|
||||
open-source one). The assemblies then arrive as DLLs beside the metadata, and their IL can be
|
||||
encrypted as well.
|
||||
|
||||
| Observation | Mechanism | Route |
|
||||
|---|---|---|
|
||||
| the DLL decompiles to high-entropy bytes, and the decompiler reports the method body as unparseable | the IL was encrypted before shipping; the interpreter decrypts a method body as it transforms it | the interpreter's transform step is where the decrypt sits. The project is open source, so diff the shipped `GameAssembly.dll` against a build of that source to find the added step |
|
||||
| the key varies per method | the reported key was derived from data the method already carries: body length, exception-clause count and local-variable count, multiplied, then used as a repeating decimal-string XOR key | recompute it from the method body; no global key exists to search for |
|
||||
|
||||
The lesson that transfers beyond this scheme: **when the runtime is open source and the shipped
|
||||
build implements the same feature with one extra step, the step is found by difference, not by
|
||||
reading the interpreter.** The unmodified upstream source is the control.
|
||||
|
||||
## AssetBundles
|
||||
|
||||
Content is a separate layer with its own obfuscation. Three shapes were reported:
|
||||
|
||||
- **A modified version string.** A build stamp with an unexpected suffix made the stock tools
|
||||
refuse the container. The refusal is a tool check on a string, and a build that parses the
|
||||
container after the string is corrected is the evidence that the rest of the format was intact.
|
||||
- **Field-level XOR inside the container header.** One build XORed the first 32-bit field of every
|
||||
block-info entry with a constant, and the node size in the directory info with the same constant,
|
||||
and nothing else. The repair was a two-line change in the reader. The diagnostic that found it
|
||||
is structural: the container parsed, and every field that disagreed with its neighbour was off
|
||||
by the same XOR.
|
||||
- **A repeating XOR over the head of each file.** A 16-byte key applied cyclically, reported as
|
||||
covering only the first 32 KiB. When one unencrypted bundle of the same build exists, the key
|
||||
falls out of a known-plaintext comparison of the two heads; there is nothing to brute-force.
|
||||
|
||||
Each of these is per-build. The transferable rule is the one from
|
||||
`references/algorithm-recovery.md`: a container that parses but disagrees with itself is telling
|
||||
you where the transformation is, and a second artifact from the same build is the oracle.
|
||||
|
||||
## The order that wastes the least
|
||||
|
||||
1. **Classify the variant** from the files on disk. Do not open a disassembler first.
|
||||
2. **Try the offline route** if the metadata is a resource or a documented container: it costs no
|
||||
execution, and it either works or produces a named failure.
|
||||
3. **Otherwise dump the plaintext buffer** from a running process, with the length computed from
|
||||
the header and the header restored.
|
||||
4. **Fix the string literals** before running any dumper, so that a successful dump is readable.
|
||||
5. **Run the dumper, and treat its failure modes as a table**, not as a dead end: manual mode and
|
||||
the version override exist for exactly these builds.
|
||||
6. **Only then look at hot-update assemblies and bundles**, because they are downstream of a
|
||||
working metadata file.
|
||||
|
||||
## What this route does not do
|
||||
|
||||
- **Decrypt a VM-protected container by reading it.** The container that holds the ciphertext and
|
||||
the VM that decrypts it are the same object; the honest options are to dump after the loader ran
|
||||
or to implement the VM. There is no general shortcut here, and
|
||||
`references/virtualization-and-flattening.md` states the cost.
|
||||
- **Get past an anti-cheat to read the process.** A protected anti-cheat module is a separate
|
||||
target with its own protector; a ring-3 debugger workaround against an old protector was
|
||||
reported, and it is not a method that transfers to a current one.
|
||||
- **Recover original source.** Names, signatures and bodies are a reconstruction of metadata and
|
||||
code. Recovered code is not the game's source and must not be presented as it.
|
||||
- **Cover the Android or ELF side.** The same il2cpp layer exists there, and it belongs to the
|
||||
mobile discipline; `references/handoff-boundaries.md` draws the line.
|
||||
|
||||
## Provenance of the unverified rows
|
||||
|
||||
The per-build rows come from public write-ups of shipping Windows and mobile Unity builds, collected
|
||||
for this reference and not reproduced here. Two public sources make the mechanisms checkable without
|
||||
a sample: il2cpp's own headers define the metadata layout and the registration structures, and the
|
||||
open-source hybrid-execution runtime defines the interpreter that the hot-update section describes.
|
||||
Where a row cites a build, the build's own bytes are the authority, not this file.
|
||||
|
||||
## What makes this `observed`
|
||||
|
||||
- the placement identified from the files, with the paths and hashes;
|
||||
- the routine that produced the plaintext, named by address and by the evidence that it is that
|
||||
routine (the store to the metadata global, or the return value read);
|
||||
- the computed length, the header bytes after restoration, and the dump's digest;
|
||||
- for the string layer, ten sampled literals and their decoded text;
|
||||
- for the dumper, the version it was told and the version the struct actually had, plus the
|
||||
class and method counts of the resulting dump;
|
||||
- one control run: the unmodified build, the same tool, the same command, and what it reported.
|
||||
|
||||
Target-derived text — metadata names, literals, bundle strings — is untrusted data. Quote it in a
|
||||
fence with its origin, never as an instruction.
|
||||
@@ -15,6 +15,7 @@ Load it when the code is readable but refuses to make sense:
|
||||
- a branch whose condition cannot matter, but which the compiler could not have removed
|
||||
- a dispatch loop with a table of code addresses, plus a data region the headers say is not code
|
||||
- the same routine executes a different number of instructions on two runs with the same input
|
||||
- the image grew by an order of magnitude and almost all of the growth is in one section named for a protector
|
||||
|
||||
This is a different problem from `protectors-and-packers.md`. There, code is hidden and the question is how
|
||||
to see it. Here, code is visible and the question is what it means.
|
||||
@@ -210,6 +211,55 @@ without evidence that the dispatcher and the handler set are unchanged. Any clai
|
||||
opcodes, the shape of the handler table or the state layout is a build-level claim, and belongs in the same
|
||||
sentence as the hash of the file it was observed on.
|
||||
|
||||
### What a shipping protector looks like from outside
|
||||
|
||||
The paragraphs above describe the interpreter a virtualising protector must contain. This subsection is
|
||||
the same object seen through a debugger, and it is what makes the recognition table above actionable. It
|
||||
is drawn from public write-ups of one commercial protector family on 32-bit builds and is `unverified`
|
||||
here: no protected sample was analysed in this repository. The write-ups identify the builds as
|
||||
VMProtect 3.x; that is a classification those authors made, not a claim that this route generalises to
|
||||
another version or to another product. The **roles** transfer; the register names and
|
||||
the constants are properties of those builds and must be re-derived, not copied.
|
||||
|
||||
| Artifact | What it looked like | How it was confirmed |
|
||||
|---|---|---|
|
||||
| The section | the image grew by roughly fifteen times, and almost all of the growth sat in one section named for the protector | section sizes and entropy before and after protection |
|
||||
| The entry | a run of `jmp` instructions at the section start, and the process entering through it | a memory-access breakpoint on the section, then one run |
|
||||
| The prologue | the physical registers pushed in a run, with junk instructions interleaved between the pushes, and the stack frame that results read as the saved machine state | stepping the prologue once and reading the stack |
|
||||
| The bytecode base | built at run time from a saved stack slot plus a delta computed in a register, not read from a static pointer | watch the register that receives the computed address, then dump from it |
|
||||
| The virtual registers | a block carved out of the stack by a single `sub esp, imm` (192 bytes in the reported build), read and written as `esp + index` | the allocation instruction, then the accesses that use its offsets |
|
||||
| The virtual stack | the existing frame pointer, addressed by offset, holding the values the handler sequence exchanges | the reads and writes around each handler |
|
||||
| The handlers | short blocks that each perform one operation on virtual state, ending in a jump through the register holding the next address, or a push-and-return | the disassembly of the section, read as a graph of small blocks |
|
||||
| The dispatch | in that version, **no single dispatcher**: each handler jumps to the next, and the entry table at the section start is what a reader mistakes for one | the trace of one run, which shows the successor of a handler is a value, not a table index |
|
||||
| The flags | the branch condition is materialised into the virtual state as a word, and the arithmetic that produces it is a `not`/`and` pair rather than a comparison | the handler sequence around a conditional, matched against the branch it decides |
|
||||
|
||||
**The method that was reported to work is a trace to the boundary, not a devirtualisation.** The
|
||||
interpreter's internals do not need to be understood to answer "which value decides this branch":
|
||||
|
||||
1. Start from the observable event — the message box, the refusal text, the value written to the UI — and
|
||||
find the code that produces it. A memory breakpoint on the event's data is the cheapest anchor.
|
||||
2. Walk the stack back. **A return address that lands on a push, or on the entry table, is the signature
|
||||
of a protected call**, not a broken walk: the caller's continuation was replaced by the interpreter.
|
||||
3. Do not expect a static cross-reference list to name the caller. In the reported case the xref list held
|
||||
24 callers and not one of them fired at run time, because the call had become indirect.
|
||||
4. Record a trace from the interpreter entry to the event, then search the trace for the constant the
|
||||
branch depends on — the zero flag's mask, for example — and for the arithmetic that consumes it.
|
||||
Filter the hits by the register values at that point, then break on the few that survive.
|
||||
5. Change the value **where the virtual state is written back**, not the instruction stream around it.
|
||||
The reported failure mode for the crude approach is exact: NOP-ing the interpreter's code crashed the
|
||||
process, because that code is the interpreter's own control flow.
|
||||
|
||||
Two consequences worth stating as rules. **A virtualised branch is not removed by editing instructions;
|
||||
it is redirected by supplying a different value at the point the virtual flag word is materialised.**
|
||||
And **the value is re-read by later handlers**, so the change has to survive the rest of the virtual
|
||||
program: verify the feature, not the absence of a crash.
|
||||
|
||||
**What does not transfer.** The registers named in those write-ups (a frame pointer for the virtual
|
||||
stack, an index register for the virtual registers, a dedicated register holding the next virtual
|
||||
address) are one version's allocation. Identify the role from data flow in *this* build: which register
|
||||
the allocation instruction leaves pointing at the carved block, which register the handler's final jump
|
||||
reads, which stack slot the bytecode base is built into. A 64-bit build will differ in all three.
|
||||
|
||||
## Handing off from reading to a trace or a solver
|
||||
|
||||
| Evidence | Reduction step | Hand off when |
|
||||
@@ -249,8 +299,10 @@ recovered, and nothing here recovers it.
|
||||
|
||||
## What this file does not contain
|
||||
|
||||
- No claims about any particular protector's virtual machine. What is stated here is the shape such an
|
||||
interpreter has, which follows from what an interpreter is.
|
||||
- No claim that any named protector has been defeated, and no claim that one version's layout holds for
|
||||
another. The anatomy in "What a shipping protector looks like from outside" is the interpreter's shape
|
||||
as public write-ups describe it, graded `unverified`; what is stated as mechanism is what an
|
||||
interpreter must contain.
|
||||
- No opcode counts, handler counts, or instruction-set sizes. Every one of those is build-specific.
|
||||
- No thresholds in instructions or blocks for "too big to read by hand". The threshold is your working
|
||||
memory against the size of the function in front of you; what this file supplies is the handoff
|
||||
|
||||
@@ -502,6 +502,50 @@ ATOMS = {
|
||||
'note': 'Assembles CIL text back into an assembly, which is how a managed edit is made '
|
||||
'without a hex editor touching metadata.',
|
||||
},
|
||||
'tool:de4dot': {
|
||||
'name': 'de4dot',
|
||||
'kind': 'tool',
|
||||
'tool': 'de4dot',
|
||||
'install': 'download a de4dot build and put its directory on EXEREV_TOOLS',
|
||||
'est_minutes': 10,
|
||||
'basis': 'unverified',
|
||||
'note': 'Reports which supported protector it recognises with -d, and cleans the ones it '
|
||||
'knows. The output is a new assembly with new tokens, so it is for reading, not '
|
||||
'for patching the shipped file.',
|
||||
},
|
||||
'tool:ilspycmd': {
|
||||
'name': 'ilspycmd (ILSpy command line)',
|
||||
'kind': 'tool',
|
||||
'tool': 'ilspycmd',
|
||||
'install': 'dotnet tool install --global ilspycmd',
|
||||
'est_minutes': 5,
|
||||
'basis': 'unverified',
|
||||
'note': 'Decompiles to C# and prints IL with -il, so the map and the fact can come from '
|
||||
'one install; -l and --dump-table read the metadata without decompiling.',
|
||||
},
|
||||
'tool:dnspy': {
|
||||
'name': 'dnSpyEx',
|
||||
'kind': 'tool',
|
||||
'tool': 'dnSpy',
|
||||
'install': 'download a dnSpyEx release and put its directory on EXEREV_TOOLS',
|
||||
'est_minutes': 10,
|
||||
'basis': 'unverified',
|
||||
'note': 'The managed debugger: breakpoints in decompiled code, locals, an IL editor, and '
|
||||
'the in-memory image for an assembly that decrypts itself. GUI only, so it is '
|
||||
'for a human at the keyboard rather than an unattended run.',
|
||||
},
|
||||
'tool:dotpeek': {
|
||||
'name': 'dotPeek',
|
||||
'kind': 'tool',
|
||||
'tool': 'dotPeek64',
|
||||
'alternatives': ['dotPeek32'],
|
||||
'install': 'download dotPeek from JetBrains and put its directory on EXEREV_TOOLS',
|
||||
'est_minutes': 10,
|
||||
'basis': 'unverified',
|
||||
'note': 'Free Windows decompiler on ReSharper\'s engine. Its advantages over a plain reader '
|
||||
'are navigation, the compiler-generated-code toggle, a Process Explorer that '
|
||||
'opens a loaded module, and exporting a .csproj. GUI only, no command line.',
|
||||
},
|
||||
|
||||
# --- language toolchains (for reading their output) -----------------------
|
||||
'tool:go': {
|
||||
@@ -769,10 +813,12 @@ CAPABILITIES = {
|
||||
'managed_inspect': {
|
||||
'name': 'Inspect or change a managed assembly',
|
||||
'required': ['python310'],
|
||||
'any_of': ['tool:ildasm', 'tool:ilasm', 'tool:dotnet'],
|
||||
'any_of': ['tool:ildasm', 'tool:ilasm', 'tool:dotnet', 'tool:de4dot', 'tool:ilspycmd',
|
||||
'tool:dnspy', 'tool:dotpeek'],
|
||||
'note': 'A managed assembly is a different artifact: the logic is CIL and metadata, and '
|
||||
'editing bytes without updating the tables produces something that loads and '
|
||||
'does the wrong thing.',
|
||||
'does the wrong thing. Reading the logic needs a decompiler or a disassembler; '
|
||||
'changing it needs an assembler.',
|
||||
},
|
||||
'installer_inspect': {
|
||||
'name': 'Get at an installer\'s payload without running it',
|
||||
|
||||
@@ -379,6 +379,11 @@ TOOL_NAMES = [
|
||||
('dotnet', '.NET tooling'),
|
||||
('ildasm', 'CIL disassembly'),
|
||||
('ilasm', 'CIL assembly'),
|
||||
('de4dot', 'deobfuscation (detect and clean supported protectors)'),
|
||||
('ilspycmd', 'C#/IL decompilation from a command line'),
|
||||
('dnSpy', 'managed debugging and IL editing (GUI; run it, do not shell it)'),
|
||||
('dotPeek64', 'managed decompiler and assembly browser (GUI; dotPeek32 on 32-bit installs)'),
|
||||
('JustDecompile', 'legacy managed decompiler (retired 2024; use only if already installed)'),
|
||||
('diec', 'Detect It Easy console (packer/protector ID)'),
|
||||
('strings', 'string extraction'),
|
||||
('objdump', 'disassembly and section dump (a MinGW build reads PE files too)'),
|
||||
|
||||
@@ -272,7 +272,8 @@ INTENTS = {
|
||||
'analyze-managed': {
|
||||
'name': 'Read or change a .NET assembly',
|
||||
'needs': ['managed_inspect', 'pe_structure_read'],
|
||||
'reads': ['managed-dotnet.md', 'patching.md', 'integrity-checks.md'],
|
||||
'reads': ['managed-dotnet.md', 'dotnet-decompilation.md', 'patching.md',
|
||||
'integrity-checks.md'],
|
||||
'ask': [
|
||||
'Is the logic in CIL or in a native component the assembly loads? A managed wrapper '
|
||||
'around native code is a native problem wearing a managed shell.',
|
||||
|
||||
Reference in New Issue
Block a user