Expose __hwasan_tag_mismatch_stub

[mmalcomson]

Summary

GCC would like to emit a function call to report a tag mismatch
rather than hard-code the brk instruction directly.

__hwasan_tag_mismatch_stub contains most of the functionality to do
this already, but requires exposure in the dynamic library.

This patch moves __hwasan_tag_mismatch_stub outside of the anonymous
namespace that it was defined in and declares it in
hwasan_interface_internal.h.

We also add the ability to pass sizes larger than 16 bytes to this
reporting function by providing a fourth parameter that is only looked
at when the size provided is not in the original accepted range.

This does not change the behaviour where it is already being called,
since the previous definition only accepted sizes up to 16 bytes and
hence the change in behaviour is not seen by existing users.
The change in declaration does not matter, since the only existing use
is in the __hwasan_tag_mismatch function written in assembly.

Tested with gcc and clang on an AArch64 vm.

[eugenis]

compiler-rt/lib/hwasan/hwasan_interface_internal.h

115

I think the _stub suffix does not make sense in a public interface function.
How about __hwasan_tag_mismatch4 - where 4 stands for the number of arguments?

compiler-rt/lib/hwasan/hwasan_linux.cpp

486

There is a pre-existing bug here: this function needs to set the is_load member.

[eugenis]

LGTM

compiler-rt/lib/hwasan/hwasan_interface_internal.h

 
 SANITIZER_INTERFACE_ATTRIBUTE
 uptr __hwasan_tag_pointer(uptr p, u8 tag);
 
 SANITIZER_INTERFACE_ATTRIBUTE
 void __hwasan_tag_mismatch(uptr addr, u8 ts);
 
 SANITIZER_INTERFACE_ATTRIBUTE
+void __hwasan_tag_mismatch_stub(uptr addr, uptr access_info,
+        uptr *registers_frame,
+        size_t outsize);
+
+SANITIZER_INTERFACE_ATTRIBUTE
 u8 __hwasan_generate_tag();
 
 // Returns the offset of the first tag mismatch or -1 if the whole range is
 // good.
 SANITIZER_INTERFACE_ATTRIBUTE
 sptr __hwasan_test_shadow(const void *x, uptr size);
 
 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE

compiler-rt/lib/hwasan/hwasan_linux.cpp

#if defined(__aarch64__)
   uc->uc_mcontext.pc += 4;
 #elif defined(__x86_64__)
 #else
 # error Unsupported architecture
 #endif
   return true;
 }
 
-// Entry point stub for interoperability between __hwasan_tag_mismatch (ASM) and
-// the rest of the mismatch handling code (C++).
-extern "C" void __hwasan_tag_mismatch_stub(uptr addr, uptr access_info,
-                                           uptr *registers_frame) {
-  AccessInfo ai;
-  ai.is_store = access_info & 0x10;
-  ai.recover = false;
-  ai.addr = addr;
-  ai.size = 1 << (access_info & 0xf);
-
-  HandleTagMismatch(ai, (uptr)__builtin_return_address(0),
-                    (uptr)__builtin_frame_address(0), nullptr, registers_frame);
-  __builtin_unreachable();
-}
-
 static void OnStackUnwind(const SignalContext &sig, const void *,
                           BufferedStackTrace *stack) {
   stack->Unwind(StackTrace::GetNextInstructionPc(sig.pc), sig.bp, sig.context,
                 common_flags()->fast_unwind_on_fatal);
 }
 
 void HwasanOnDeadlySignal(int signo, void *info, void *context) {
   // Probably a tag mismatch.
   if (signo == SIGTRAP)
     if (HwasanOnSIGTRAP(signo, (siginfo_t *)info, (ucontext_t*)context))
       return;
 
   HandleDeadlySignal(info, context, GetTid(), &OnStackUnwind, nullptr);
 }
 
 
 } // namespace __hwasan
 
+// Entry point stub for interoperability between __hwasan_tag_mismatch (ASM) and
+// the rest of the mismatch handling code (C++).
+void __hwasan_tag_mismatch_stub(uptr addr, uptr access_info,
+        uptr *registers_frame,
+        size_t outsize) {
+  __hwasan::AccessInfo ai;
+  ai.is_store = access_info & 0x10;
+  ai.recover = access_info & 0x20;
+  ai.addr = addr;
+  if ((access_info & 0xf) == 0xf)
+    ai.size = outsize;
+  else
+    ai.size = 1 << (access_info & 0xf);
+
+
+  __hwasan::HandleTagMismatch(ai,
+            (uptr)__builtin_return_address(0),
+            (uptr)__builtin_frame_address(0),
+            nullptr,
+            registers_frame);
+  __builtin_unreachable();
+}
+
 #endif // SANITIZER_FREEBSD || SANITIZER_LINUX || SANITIZER_NETBSD