[compiler-rt] [asan] Rewrite Windows/heaprealloc_alloc_zero check to avoid dereference (PR #156211)

[Thurston Dang via llvm-commits]

https://github.com/thurstond updated https://github.com/llvm/llvm-project/pull/156211

>From cb5e1f2dbdf4b605b60ade0ec1a1b976ac1a1cb6 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Sat, 30 Aug 2025 21:49:40 +0000
Subject: [PATCH 1/2] [asan] Rewrite Windows/heaprealloc_alloc_zero check to
 avoid dereference

The test checks that 1-byte is allocated when malloc(0) is called, by
dereferencing the pointer.
https://github.com/llvm/llvm-project/pull/155943 changed ASan to
consider the dereference to be a heap buffer overflow. This patch
changes the test to check the allocated size is still 1-byte, but not dereference the
pointer.

This aims to fix the breakage reported in https://github.com/llvm/llvm-project/pull/155943#issuecomment-3239543505
---
 .../asan/TestCases/Windows/heaprealloc_alloc_zero.cpp     | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp b/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp
index 8b0bc71b9f5db..e9be0d5b4c7df 100644
--- a/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp
+++ b/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp
@@ -3,13 +3,19 @@
 // UNSUPPORTED: asan-64-bits
 #include <cassert>
 #include <iostream>
+#include <sanitizer/allocator_interface.h>
 #include <windows.h>
 
 int main() {
   void *ptr = malloc(0);
   if (ptr)
     std::cerr << "allocated!\n";
-  ((char *)ptr)[0] = '\xff'; //check this 'allocate 1 instead of 0' hack hasn't changed
+
+  // Check the 'allocate 1 instead of 0' hack hasn't changed
+  // Note that as of b3452d90b043a398639e62b0ab01aa339cc649de, dereferencing
+  // the pointer will be detected as a heap-buffer-overflow.
+  if (__sanitizer_get_allocated_size(ptr) != 1)
+    return 1;
 
   free(ptr);
 

>From cc22e49b177c884db9ac80da92820ebf63955c20 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Sat, 30 Aug 2025 22:20:22 +0000
Subject: [PATCH 2/2] Enable test for 64-bit Windows as well (Reported to work
 in https://github.com/llvm/llvm-project/pull/156211#issuecomment-3239575112)

---
 .../test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp       | 1 -
 1 file changed, 1 deletion(-)

diff --git a/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp b/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp
index e9be0d5b4c7df..6a5f8a1e7ea09 100644
--- a/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp
+++ b/compiler-rt/test/asan/TestCases/Windows/heaprealloc_alloc_zero.cpp
@@ -1,6 +1,5 @@
 // RUN: %clang_cl_asan %Od %MT -o %t %s
 // RUN: %env_asan_opts=windows_hook_rtl_allocators=true %run %t 2>&1 | FileCheck %s
-// UNSUPPORTED: asan-64-bits
 #include <cassert>
 #include <iostream>
 #include <sanitizer/allocator_interface.h>