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[libunwind] Inform ASan that resumption is noreturn

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If you're building libunwind instrumented with ASan, `_Unwind_RaiseException`
will poison the stack and then transfer control in a manner which isn't
understood by ASan, so the stack will remain poisoned. This can cause
false positives, e.g. if you call an uninstrumented function (so it
doesn't re-poison the stack) after catching an exception. Add a call to
`__asan_handle_no_return` inside `__unw_resume` to get ASan to unpoison
the stack and avoid this.

`__unw_resume` seems like the appropriate place to make this call, since
it's used for resumption by all unwind implementations except SJLJ. SJLJ
uses `__builtin_longjmp` to handle resumption, which is already
recognized as noreturn (and therefore ASan adds the `__asan_handle_no_return`
call itself), so it doesn't need any special handling.

PR32434 is somewhat similar (in particular needing a component built
without ASan to trigger the bug), and rG781ef03e1012, the fix for that
bug, adds an interceptor for `_Unwind_RaiseException`. This interceptor
won't always be triggered though, e.g. if you statically link the
unwinder into libc++abi in a way that prevents interposing the unwinder
functions (e.g. marking the symbols as hidden, using `--exclude-libs`,
or using `-Bsymbolic`). rG53335d6d86d5 makes `__cxa_throw` call
`__asan_handle_no_return` explicitly, to similarly avoid relying on
interception.

Reviewed By: #libunwind, compnerd

Differential Revision: https://reviews.llvm.org/D103002
This commit is contained in:
Shoaib Meenai 2021-05-23 20:41:57 -07:00
parent d28bc54ff4
commit adf1561d6c
1 changed files with 7 additions and 0 deletions
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7
libunwind/src/libunwind.cpp
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@ -16,6 +16,9 @@
#include <stdlib.h>
#if __has_feature(address_sanitizer)
#include <sanitizer/asan_interface.h>
#endif
#if !defined(__USING_SJLJ_EXCEPTIONS__)
#include "AddressSpace.hpp"
@ -184,6 +187,10 @@ _LIBUNWIND_WEAK_ALIAS(__unw_get_proc_info, unw_get_proc_info)
/// Resume execution at cursor position (aka longjump).
_LIBUNWIND_HIDDEN int __unw_resume(unw_cursor_t *cursor) {
_LIBUNWIND_TRACE_API("__unw_resume(cursor=%p)", static_cast<void *>(cursor));
#if __has_feature(address_sanitizer)
// Inform the ASan runtime that now might be a good time to clean stuff up.
__asan_handle_no_return();
#endif
AbstractUnwindCursor *co = (AbstractUnwindCursor *)cursor;
co->jumpto();
return UNW_EUNSPEC;