Arm64:[PAC-RET]Fix ARM64 epilog detection and PAC signing SP recovery - #135088
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Fixes: dotnet#134912 - Stop treating SP adjustments as evidence of an epilog: they may occur during stack allocation in the function body. - Continue rejecting hijacking after FP or LR has been restored. - For NativeAOT assert that signing SP equals CFA. - Use the caller SP recovered by unwinding to sign hijacked return addresses. This avoids reconstructing signing SP from frame offsets.
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Tagging subscribers to this area: @agocke, @dotnet/ilc-contrib |
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cc: @dotnet/arm64-contrib @jkotas @dhartglassMSFT |
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Copilot review overview
🟡 Changes recommended
The new CFA invariant breaks PAC-enabled ARM64 OSR prologs and can produce invalid hijack signatures.
Review effort: Balanced
Findings: 1
Open (1)
What changed in this PR
Fixes ARM64 PAC return-address hijacking and epilog detection in NativeAOT.
Changes:
- Refines ARM64 epilog detection.
- Recovers PAC signing SP through unwinding.
- Adds signing-SP/CFA assertions.
| File | Description |
|---|---|
CorInfoImpl.RyuJit.cs |
Validates PAC CFI assumptions. |
UnixNativeCodeManager.cpp |
Updates epilog detection and PAC signing-SP recovery. |
unwindarm64.cpp |
Asserts PAC occurs before frame setup. |
| UNATIVE_OFFSET cbProlog = unwindGetCurrentOffset(func); | ||
| // Sign before frame setup so signing SP == CFA. | ||
| // Stack probes may precede PAC because they do not change SP. | ||
| assert(func->cfiCodes->empty()); |
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This check is in generateCFIUnwindCodes() that's true on Unix NativeAOT. We do not have OSR for NativeAOT so it's safe to assert no cfi codes are present to ensure SP == CFA.
jkotas
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Oct 2, 2026
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/azp run runtime-nativeaot-outerloop |
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Azure Pipelines: Successfully started running 1 pipeline(s). |
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Fixes: #134912