Unpoison alloca used in stack adjustments when ASAN#839
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The pattern for several of the architectures is for ffi_call_int to stack-allocate some arguments + the registers, and then ffi_call_$ARCH will pop the top of that structure into registers, and then adjust the stack pointer such that the alloca'd buffer _becomes_ the stack-passed arguments for the function being called. If libffi is compiled with ASAN, then there will be a redzone inserted after the alloca'd buffer which is marked as poisoned. This redzone appears beyond the end of $sp upon entry to the called function. If the called function does anything to use this stack memory, ASAN will notice that it's poisoned and report an error. This commit fixes the situation (on the architectures that I have access to) by manually unpoisoning the alloca'd buffer's redzone. The alternative approach would be to disable instrumentation for ffi_call_int altogether, which I can also do if we think that's preferable.
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Thank you for this work. My preference, however, is to disable instrumentation. Can you generate a patch for this along the lines of what was discussed in #255 ? |
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Easily done - I opened a new PR with that: #858 |
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The pattern for several of the architectures is for ffi_call_int to stack-allocate some arguments + the registers, and then ffi_call_$ARCH will pop the top of that structure into registers, and then adjust the stack pointer such that the alloca'd buffer becomes the stack-passed arguments for the function being called.
If libffi is compiled with ASAN, then there will be a redzone inserted after the alloca'd buffer which is marked as poisoned. This redzone appears beyond the end of $sp upon entry to the called function.
If the called function does anything to use this stack memory, ASAN will notice that it's poisoned and report an error.
This commit fixes the situation (on the architectures that I have access to) by manually unpoisoning the alloca'd buffer's redzone. The alternative approach would be to disable instrumentation for ffi_call_int altogether, which I can also do if we think that's preferable.
This should fix the issue reported in #255