Poison last word of FakeFrame

[brandb97]

Fix issue#133640

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[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (brandb97)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/133689.diff

1 Files Affected:

• (modified) compiler-rt/lib/asan/asan_fake_stack.cpp (+6-1)

diff --git a/compiler-rt/lib/asan/asan_fake_stack.cpp b/compiler-rt/lib/asan/asan_fake_stack.cpp
index 7443ff166984d..f68dd31ab1610 100644
--- a/compiler-rt/lib/asan/asan_fake_stack.cpp
+++ b/compiler-rt/lib/asan/asan_fake_stack.cpp
@@ -107,7 +107,12 @@ FakeFrame *FakeStack::Allocate(uptr stack_size_log, uptr class_id,
     FakeFrame *res = reinterpret_cast<FakeFrame *>(
         GetFrame(stack_size_log, class_id, pos));
     res->real_stack = real_stack;
-    *SavedFlagPtr(reinterpret_cast<uptr>(res), class_id) = &flags[pos];
+    u8 **saved_flag_ptr = SavedFlagPtr(reinterpret_cast<uptr>(res), class_id);
+    *saved_flag_ptr = &flags[pos];
+
+    // Poison the last word of FakeFrame
+    u8 *shadow = reinterpret_cast<u8*>(MemToShadow(reinterpret_cast<uptr>(saved_flag_ptr)));
+    *shadow = kMagic1;
     return res;
   }
   return nullptr; // We are out of fake stack.

[brandb97]

@vitalybuka @ramosian-glider

[brandb97]

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