[hwasan] An LLVM flag to disable stack tag randomization.

[eugenis]

Summary

Necessary to achieve consistent test results.

[eugenis]

Generated code is not great with this flag. If performance was a goal, some things could be done differently.
I've tried to share as much code with with the randomized-tags path as possible.

lib/hwasan/hwasan.cc

 void __hwasan_store16_noabort(uptr p) {
   CheckAddress<ErrorAction::Recover, AccessType::Store, 4>(p);
 }
 
 void __hwasan_tag_memory(uptr p, u8 tag, uptr sz) {
   TagMemoryAligned(p, sz, tag);
 }
 
+static const u8 kFallbackTag = 0xBB;
+
+u8 __hwasan_generate_tag() {
+  HwasanThread *t = GetCurrentThread();
+  if (!t) return kFallbackTag;
+  return t->GenerateRandomTag();
+}
+
 #if !SANITIZER_SUPPORTS_WEAK_HOOKS
 extern "C" {
 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 const char* __hwasan_default_options() { return ""; }
 }  // extern "C"
 #endif
 
 extern "C" {
 SANITIZER_INTERFACE_ATTRIBUTE
 void __sanitizer_print_stack_trace() {
   GET_FATAL_STACK_TRACE_PC_BP(StackTrace::GetCurrentPc(), GET_CURRENT_FRAME());
   stack.Print();
 }
 } // extern "C"

lib/hwasan/hwasan_interface_internal.h

 SANITIZER_INTERFACE_ATTRIBUTE
 void __hwasan_store8_noabort(uptr);
 SANITIZER_INTERFACE_ATTRIBUTE
 void __hwasan_store16_noabort(uptr);
 
 SANITIZER_INTERFACE_ATTRIBUTE
 void __hwasan_tag_memory(uptr p, u8 tag, uptr sz);
 
+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
 /* OPTIONAL */ const char* __hwasan_default_options();
 

test/hwasan/lit.cfg

 # -*- Python -*-
 
 import os
 
 # Setup config name.
 config.name = 'HWAddressSanitizer' + getattr(config, 'name_suffix', 'default')
 
 # Setup source root.
 config.test_source_root = os.path.dirname(__file__)
 
 # Setup default compiler flags used with -fsanitize=memory option.
-clang_hwasan_cflags = ["-fsanitize=hwaddress", config.target_cflags] + config.debug_info_flags
+clang_hwasan_cflags = ["-fsanitize=hwaddress", "-mllvm", "-hwasan-generate-tags-with-calls", config.target_cflags] + config.debug_info_flags
 clang_hwasan_cxxflags = config.cxx_mode_flags + clang_hwasan_cflags
 
 def build_invocation(compile_flags):
   return " " + " ".join([config.clang] + compile_flags) + " "
 
 config.substitutions.append( ("%clang_hwasan ", build_invocation(clang_hwasan_cflags)) )
 config.substitutions.append( ("%clangxx_hwasan ", build_invocation(clang_hwasan_cxxflags)) )