From acb0073adc55a535bcdef530c0bd9557754aa524 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka@google.com>
Date: Fri, 22 Sep 2023 10:35:12 -0700
Subject: [PATCH] [hwasan] Fixing false invalid-free with disabled tagging

This problem was accidentally discovered by the internal symbolizer, but
it's relevant for external one as well, see the test.

If we just disable tagging, there may still be tagged allocations that
have already been freed. After disabling tagging, these tagged
allocations can be released to the user as-is, which would later break
the "invalid-free" check.

We cannot just disable the "invalid-free" check with disabled tagging,
because if we re-enable tagging, the issue still applies to allocations
created when it was disabled.

The fix is to continue tagging with zero even if tagging is disabled.

This makes the "disabled" mode less efficient, but this is not the
primary use case.
---
 compiler-rt/lib/hwasan/hwasan_allocator.cpp   | 35 +++++++---------
 .../test/hwasan/TestCases/enable-disable.c    | 42 +++++++++++++++++++
 2 files changed, 57 insertions(+), 20 deletions(-)
 create mode 100644 compiler-rt/test/hwasan/TestCases/enable-disable.c

diff --git a/compiler-rt/lib/hwasan/hwasan_allocator.cpp b/compiler-rt/lib/hwasan/hwasan_allocator.cpp
index c99d730e059fa..d21ba024a20e1 100644
--- a/compiler-rt/lib/hwasan/hwasan_allocator.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_allocator.cpp
@@ -234,28 +234,23 @@ static void *HwasanAllocate(StackTrace *stack, uptr orig_size, uptr alignment,
   }
 
   void *user_ptr = allocated;
-  // Tagging can only be skipped when both tag_in_malloc and tag_in_free are
-  // false. When tag_in_malloc = false and tag_in_free = true malloc needs to
-  // retag to 0.
   if (InTaggableRegion(reinterpret_cast<uptr>(user_ptr)) &&
-      (flags()->tag_in_malloc || flags()->tag_in_free) &&
-      atomic_load_relaxed(&hwasan_allocator_tagging_enabled)) {
-    if (flags()->tag_in_malloc && malloc_bisect(stack, orig_size)) {
-      tag_t tag = t ? t->GenerateRandomTag() : kFallbackAllocTag;
-      uptr tag_size = orig_size ? orig_size : 1;
-      uptr full_granule_size = RoundDownTo(tag_size, kShadowAlignment);
-      user_ptr =
-          (void *)TagMemoryAligned((uptr)user_ptr, full_granule_size, tag);
-      if (full_granule_size != tag_size) {
-        u8 *short_granule =
-            reinterpret_cast<u8 *>(allocated) + full_granule_size;
-        TagMemoryAligned((uptr)short_granule, kShadowAlignment,
-                         tag_size % kShadowAlignment);
-        short_granule[kShadowAlignment - 1] = tag;
-      }
-    } else {
-      user_ptr = (void *)TagMemoryAligned((uptr)user_ptr, size, 0);
+      atomic_load_relaxed(&hwasan_allocator_tagging_enabled) &&
+      flags()->tag_in_malloc && malloc_bisect(stack, orig_size)) {
+    tag_t tag = t ? t->GenerateRandomTag() : kFallbackAllocTag;
+    uptr tag_size = orig_size ? orig_size : 1;
+    uptr full_granule_size = RoundDownTo(tag_size, kShadowAlignment);
+    user_ptr = (void *)TagMemoryAligned((uptr)user_ptr, full_granule_size, tag);
+    if (full_granule_size != tag_size) {
+      u8 *short_granule = reinterpret_cast<u8 *>(allocated) + full_granule_size;
+      TagMemoryAligned((uptr)short_granule, kShadowAlignment,
+                       tag_size % kShadowAlignment);
+      short_granule[kShadowAlignment - 1] = tag;
     }
+  } else {
+    // Tagging can not be completely skipped. If it's disabled, we need to tag
+    // with zeros.
+    user_ptr = (void *)TagMemoryAligned((uptr)user_ptr, size, 0);
   }
 
   Metadata *meta =
diff --git a/compiler-rt/test/hwasan/TestCases/enable-disable.c b/compiler-rt/test/hwasan/TestCases/enable-disable.c
new file mode 100644
index 0000000000000..290ce07656a60
--- /dev/null
+++ b/compiler-rt/test/hwasan/TestCases/enable-disable.c
@@ -0,0 +1,42 @@
+// Test that disabling/enabling tagging does not trigger false reports on
+// allocations happened in a different state.
+
+// RUN: %clang_hwasan -O1 %s -o %t && %run %t 2>&1
+
+#include <assert.h>
+#include <sanitizer/hwasan_interface.h>
+#include <stdlib.h>
+
+enum {
+  COUNT = 5,
+  SZ = 10,
+};
+void *x[COUNT];
+
+int main() {
+  __hwasan_enable_allocator_tagging();
+  for (unsigned i = 0; i < COUNT; ++i) {
+    x[i] = malloc(SZ);
+    assert(__hwasan_test_shadow(x[i], SZ) == -1);
+  }
+  for (unsigned i = 0; i < COUNT; ++i)
+    free(x[i]);
+
+  __hwasan_disable_allocator_tagging();
+  for (unsigned i = 0; i < COUNT; ++i) {
+    x[i] = malloc(SZ);
+    assert(__hwasan_tag_pointer(x[i], 0) == x[i]);
+    assert(__hwasan_test_shadow(x[i], SZ) == -1);
+  }
+  for (unsigned i = 0; i < COUNT; ++i)
+    free(x[i]);
+
+  __hwasan_enable_allocator_tagging();
+  for (unsigned i = 0; i < COUNT; ++i) {
+    x[i] = malloc(SZ);
+    assert(__hwasan_test_shadow(x[i], SZ) == -1);
+  }
+  for (unsigned i = 0; i < COUNT; ++i)
+    free(x[i]);
+  return 0;
+}