[HWASAN] Fix HwasanReallocate in aliasing mode

[vitalybuka]

Summary

HWASAN_ALIASING_MODE needs to untag only
primary allocator pointers.

[thurston]

compiler-rt/lib/hwasan/hwasan_allocator.cpp

387–393

This "Untag pointer iff it is in a taggable region" idiom is used often enough (e.g., also in AllocationSize and AllocationBegin of https://reviews.llvm.org/D149238) that it might be worth having a helper function.

[vitalybuka]

compiler-rt/lib/hwasan/hwasan_allocator.cpp

387–393

Addressing in followup patches

[vitalybuka]

compiler-rt/lib/hwasan/hwasan_allocator.cpp

387–393

D149305

compiler-rt/lib/hwasan/hwasan_allocator.cpp

void *untagged_ptr_old =
           : tagged_ptr_old;
   if (CheckInvalidFree(stack, untagged_ptr_old, tagged_ptr_old))
     return nullptr;
   void *tagged_ptr_new =
       HwasanAllocate(stack, new_size, alignment, false /*zeroise*/);
   if (tagged_ptr_old && tagged_ptr_new) {
     Metadata *meta =
         reinterpret_cast<Metadata *>(allocator.GetMetaData(untagged_ptr_old));
-    internal_memcpy(
-        UntagPtr(tagged_ptr_new), untagged_ptr_old,
+    void *untagged_ptr_new =
+        InTaggableRegion(reinterpret_cast<uptr>(tagged_ptr_new))
+            ? UntagPtr(tagged_ptr_new)
+            : tagged_ptr_new;
+    internal_memcpy(untagged_ptr_new, untagged_ptr_old,
                     Min(new_size, static_cast<uptr>(meta->GetRequestedSize())));
     HwasanDeallocate(stack, tagged_ptr_old);
   }
   return tagged_ptr_new;
 }
 
 static void *HwasanCalloc(StackTrace *stack, uptr nmemb, uptr size) {
   if (UNLIKELY(CheckForCallocOverflow(size, nmemb))) {
     if (AllocatorMayReturnNull())
       return nullptr;

compiler-rt/test/sanitizer_common/TestCases/max_allocation_size.cpp

 // RUN: %env_tool_opts=max_allocation_size_mb=2:allocator_may_return_null=0 \
 // RUN:   not %run %t strndup 2>&1 | FileCheck %s --check-prefix=CHECK-sCRASH
 // RUN: %env_tool_opts=max_allocation_size_mb=2:allocator_may_return_null=1 \
 // RUN:   %run %t strndup 2>&1 | FileCheck %s --check-prefix=CHECK-NULL
 
 // win32 is disabled due to failing errno tests.
 // UNSUPPORTED: ubsan, target={{.*windows-msvc.*}}
 
-// FIXME: Something crashes.
-// XFAIL: hwasan-aliasing
-
 #include <assert.h>
 #include <errno.h>
 #include <limits>
 #include <new>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>