[ASan] Do not instrument catch block parameters on Windows

compiler-rt/test/asan/TestCases/Windows/basic_exception_handling.cpp

@@ -0,0 +1,33 @@
+// RUN: %clangxx_asan %s -o %t
+// RUN: %run %t | FileCheck %s
+
+// This test tests that declaring a parameter in a catch-block does not produce a false positive
+// ASan error on Windows.
+
+// This code is based on the repro in https://github.com/google/sanitizers/issues/749
+#include <cstdio>
+#include <exception>
+
+void throwInFunction() { throw std::exception("test2"); }
+
+int main() {
+  // case 1: direct throw
+  try {
+    throw std::exception("test1");
+  } catch (const std::exception &ex) {
+    puts(ex.what());
+    // CHECK: test1
+  }
+
+  // case 2: throw in function
+  try {
+    throwInFunction();
+  } catch (const std::exception &ex) {
+    puts(ex.what());
+    // CHECK: test2
+  }
+
+  printf("Success!\n");
+  // CHECK: Success!
+  return 0;
+}

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -850,6 +850,7 @@ struct AddressSanitizer {
   bool maybeInsertAsanInitAtFunctionEntry(Function &F);
   bool maybeInsertDynamicShadowAtFunctionEntry(Function &F);
   void markEscapedLocalAllocas(Function &F);
+  void markCatchParametersAsUninteresting(Function &F);
 
 private:
   friend struct FunctionStackPoisoner;
@@ -2986,6 +2987,24 @@ void AddressSanitizer::markEscapedLocalAllocas(Function &F) {
     }
   }
 }
+// Mitigation for https://github.com/google/sanitizers/issues/749
+// We don't instrument Windows catch-block parameters to avoid
+// interfering with exception handling assumptions.
+void AddressSanitizer::markCatchParametersAsUninteresting(Function &F) {
+  for (BasicBlock &BB : F) {
+    for (Instruction &I : BB) {
+      if (auto *CatchPad = dyn_cast<CatchPadInst>(&I)) {
+        // Mark the parameters to a catch-block as uninteresting to avoid
+        // instrumenting them
+        for (Value *Operand : CatchPad->arg_operands()) {
+          if (auto *AI = dyn_cast<AllocaInst>(Operand)) {
+            ProcessedAllocas[AI] = false;
+          }
+        }
+      }
+    }
+  }
+}
 
 bool AddressSanitizer::suppressInstrumentationSiteForDebug(int &Instrumented) {
   bool ShouldInstrument =
@@ -3030,6 +3049,9 @@ bool AddressSanitizer::instrumentFunction(Function &F,
   // can be passed to that intrinsic.
   markEscapedLocalAllocas(F);
 
+  if (TargetTriple.isOSWindows())
+    markCatchParametersAsUninteresting(F);
+
   // We want to instrument every address only once per basic block (unless there
   // are calls between uses).
   SmallPtrSet<Value *, 16> TempsToInstrument;