Fix libmemunreachable vs hwasan conflict.

* Scan memory in a non-sanitized function.
* Don't scan hwasan shadow mappings.
  Shadow is ~33G and never contains any heap pointers. The scan takes
  about a minute on my device.

Bug: 112438058
Test: memunreachable_test with SANITIZE_TARGET=hwaddress
      the test still fails, but now there are no hwasan reports or new
      tombstones, and it completes in less than a minute

Change-Id: Ibe4811c67609ca9fe317edc250993b915570a638

2 files changed, 14 insertions, 2 deletions

diff --git a/libmemunreachable/HeapWalker.cpp b/libmemunreachable/HeapWalker.cpp
index 89837f7d2..e11f0798a 100644
--- a/libmemunreachable/HeapWalker.cpp
+++ b/libmemunreachable/HeapWalker.cpp
@@ -59,12 +59,19 @@ bool HeapWalker::Allocation(uintptr_t begin, uintptr_t end) {
   }
 }
 
+// Sanitizers may consider certain memory inaccessible through certain pointers.
+// With MTE this will need to use unchecked instructions or disable tag checking globally.
+static uintptr_t ReadWordAtAddressUnsafe(uintptr_t word_ptr)
+    __attribute__((no_sanitize("address", "hwaddress"))) {
+  return *reinterpret_cast<uintptr_t*>(word_ptr);
+}
+
 bool HeapWalker::WordContainsAllocationPtr(uintptr_t word_ptr, Range* range, AllocationInfo** info) {
   walking_ptr_ = word_ptr;
   // This access may segfault if the process under test has done something strange,
   // for example mprotect(PROT_NONE) on a native heap page.  If so, it will be
   // caught and handled by mmaping a zero page over the faulting page.
-  uintptr_t value = *reinterpret_cast<uintptr_t*>(word_ptr);
+  uintptr_t value = ReadWordAtAddressUnsafe(word_ptr);
   walking_ptr_ = 0;
   if (value >= valid_allocations_range_.begin && value < valid_allocations_range_.end) {
     AllocationMap::iterator it = allocations_.find(Range{value, value + 1});
diff --git a/libmemunreachable/MemUnreachable.cpp b/libmemunreachable/MemUnreachable.cpp
index 3d7b8a8aa..299c320ac 100644
--- a/libmemunreachable/MemUnreachable.cpp
+++ b/libmemunreachable/MemUnreachable.cpp
@@ -217,6 +217,10 @@ static bool has_prefix(const allocator::string& s, const char* prefix) {
   return ret == 0;
 }
 
+static bool is_sanitizer_mapping(const allocator::string& s) {
+  return s == "[anon:low shadow]" || s == "[anon:high shadow]" || has_prefix(s, "[anon:hwasan");
+}
+
 bool MemUnreachable::ClassifyMappings(const allocator::vector<Mapping>& mappings,
                                       allocator::vector<Mapping>& heap_mappings,
                                       allocator::vector<Mapping>& anon_mappings,
@@ -258,7 +262,8 @@ bool MemUnreachable::ClassifyMappings(const allocator::vector<Mapping>& mappings
     } else if (mapping_name.size() == 0) {
       globals_mappings.emplace_back(*it);
     } else if (has_prefix(mapping_name, "[anon:") &&
-               mapping_name != "[anon:leak_detector_malloc]") {
+               mapping_name != "[anon:leak_detector_malloc]" &&
+               !is_sanitizer_mapping(mapping_name)) {
       // TODO(ccross): it would be nice to treat named anonymous mappings as
       // possible leaks, but naming something in a .bss or .data section makes
       // it impossible to distinguish them from mmaped and then named mappings.