[HWASan] Do not retag allocas before return from the function.
Summary:
Retagging allocas before returning from the function might help
detecting use after return bugs, but it does not work at all in real
life, when instrumented and non-instrumented code is intermixed.
Consider the following code:
F_non_instrumented() {
T x;
F1_instrumented(&x);
...
}
{
F_instrumented();
F_non_instrumented();
}
- F_instrumented call leaves the stack below the current sp tagged
randomly for UAR detection
- F_non_instrumented allocates its own vars on that tagged stack,
not generating any tags, that is the address of x has tag 0, but the
shadow memory still contains tags left behind by F_instrumented on the
previous step
- F1_instrumented verifies &x before using it and traps on tag mismatch,
0 vs whatever tag was set by F_instrumented
Reviewers: eugenis
Subscribers: srhines, llvm-commits
Differential Revision: https://reviews.llvm.org/D48664
llvm-svn: 336011
diff --git a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
index a1205d8..d62598b 100644
--- a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -95,6 +95,14 @@
cl::desc("instrument stack (allocas)"),
cl::Hidden, cl::init(true));
+static cl::opt<bool> ClUARRetagToZero(
+ "hwasan-uar-retag-to-zero",
+ cl::desc("Clear alloca tags before returning from the function to allow "
+ "non-instrumented and instrumented function calls mix. When set "
+ "to false, allocas are retagged before returning from the "
+ "function to detect use after return."),
+ cl::Hidden, cl::init(true));
+
static cl::opt<bool> ClGenerateTagsWithCalls(
"hwasan-generate-tags-with-calls",
cl::desc("generate new tags with runtime library calls"), cl::Hidden,
@@ -577,6 +585,8 @@
}
Value *HWAddressSanitizer::getUARTag(IRBuilder<> &IRB, Value *StackTag) {
+ if (ClUARRetagToZero)
+ return ConstantInt::get(IntptrTy, 0);
if (ClGenerateTagsWithCalls)
return getNextTagWithCall(IRB);
return IRB.CreateXor(StackTag, ConstantInt::get(IntptrTy, 0xFFU));