[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

@@ -1397,6 +1397,16 @@ void AddressSanitizer::instrumentMemIntrinsic(MemIntrinsic *MI,
   MI->eraseFromParent();
 }
 
+// Check if an alloca is a catch block parameter
+static bool isCatchParameter(const AllocaInst &AI) {
+  for (const Use &U : AI.uses()) {
+    if (isa<CatchPadInst>(U.getUser())) {
+      return true;
+    }
+  }
+  return false;
+}
+
 /// Check if we want (and can) handle this alloca.
 bool AddressSanitizer::isInterestingAlloca(const AllocaInst &AI) {
   auto [It, Inserted] = ProcessedAllocas.try_emplace(&AI);
@@ -1417,7 +1427,11 @@ bool AddressSanitizer::isInterestingAlloca(const AllocaInst &AI) {
        // swifterror allocas are register promoted by ISel
        !AI.isSwiftError() &&
        // safe allocas are not interesting
-       !(SSGI && SSGI->isSafe(AI)));
+       !(SSGI && SSGI->isSafe(AI)) &&
+       // Mitigation for https://github.com/google/sanitizers/issues/749
+       // We don't instrument Windows catch-block parameters to avoid
+       // interfering with exception handling assumptions.
+       !(TargetTriple.isOSWindows() && isCatchParameter(AI)));
 
   It->second = IsInteresting;
   return IsInteresting;