[tsan] Fix calculation of shadow end address in MemoryAccessRangeT (#98404)
MemoryAccessRangeT overestimates the size of the shadow region by 8x,
occasionally leading to assertion failure:
```
RawShadow* shadow_mem = MemToShadow(addr);
...
// Check that end of shadow is valid
if (!IsShadowMem(shadow_mem + size * kShadowCnt - 1)) {
DCHECK(IsShadowMem(shadow_mem + size * kShadowCnt - 1));
```
It is erroneous for two separate reasons:
- it uses kShadowCnt (== 4) instead of kShadowMultiplier (== 2)
- since shadow_mem is a RawShadow*, pointer arithmetic is multiplied by
sizeof(RawShadow) == 4
This patch fixes the calculation, and also improves the debugging
information.
The assertion error was observed on a buildbot
(https://lab.llvm.org/staging/#/builders/89/builds/656/steps/13/logs/stdio):
```
Bad shadow addr 0x3000000190bc (7fffffffe85f)
ThreadSanitizer: CHECK failed: tsan_rtl_access.cpp:690 "((IsShadowMem(shadow_mem + size * kShadowCnt - 1))) != (0)" (0x0, 0x0) (tid=2202676)
```
Notice that 0x3000000190bc is not the correct shadow for the end address
0x7fffffffe85f.
This error is more commonly observed on high-entropy ASLR systems, since
ASLR may be disabled (if the randomized memory layout is incompatible),
leading to an allocation near the boundaries of the high app memory
region (and therefore a shadow end that may be erroneously calculated to
be past the end of the shadow region). Also note that the assertion is
guarded by SANITIZER_DEBUG.
---------
Co-authored-by: Vitaly Buka <vitalybuka@gmail.com>diff --git a/compiler-rt/lib/tsan/rtl/tsan_rtl_access.cpp b/compiler-rt/lib/tsan/rtl/tsan_rtl_access.cpp
index 8b20984..cf07686 100644
--- a/compiler-rt/lib/tsan/rtl/tsan_rtl_access.cpp
+++ b/compiler-rt/lib/tsan/rtl/tsan_rtl_access.cpp
@@ -672,22 +672,28 @@
#if SANITIZER_DEBUG
if (!IsAppMem(addr)) {
- Printf("Access to non app mem %zx\n", addr);
+ Printf("Access to non app mem start: %p\n", (void*)addr);
DCHECK(IsAppMem(addr));
}
if (!IsAppMem(addr + size - 1)) {
- Printf("Access to non app mem %zx\n", addr + size - 1);
+ Printf("Access to non app mem end: %p\n", (void*)(addr + size - 1));
DCHECK(IsAppMem(addr + size - 1));
}
if (!IsShadowMem(shadow_mem)) {
- Printf("Bad shadow addr %p (%zx)\n", static_cast<void*>(shadow_mem), addr);
+ Printf("Bad shadow start addr: %p (%p)\n", shadow_mem, (void*)addr);
DCHECK(IsShadowMem(shadow_mem));
}
- if (!IsShadowMem(shadow_mem + size * kShadowCnt - 1)) {
- Printf("Bad shadow addr %p (%zx)\n",
- static_cast<void*>(shadow_mem + size * kShadowCnt - 1),
- addr + size - 1);
- DCHECK(IsShadowMem(shadow_mem + size * kShadowCnt - 1));
+
+ RawShadow* shadow_mem_end = reinterpret_cast<RawShadow*>(
+ reinterpret_cast<uptr>(shadow_mem) + size * kShadowMultiplier - 1);
+ if (!IsShadowMem(shadow_mem_end)) {
+ Printf("Bad shadow end addr: %p (%p)\n", shadow_mem_end,
+ (void*)(addr + size - 1));
+ Printf(
+ "Shadow start addr (ok): %p (%p); size: 0x%zx; kShadowMultiplier: "
+ "%zx\n",
+ shadow_mem, (void*)addr, size, kShadowMultiplier);
+ DCHECK(IsShadowMem(shadow_mem_end));
}
#endif
