[compiler-rt] [PAC][compiler-rt][UBSan] Strip signed vptr instead of authenticating it (PR #100153)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Akira Hatanaka (ahatanak)

<details>
<summary>Changes</summary>

vtpr cannot be authenticated without knowing the class type if it was signed with type discrimination.

Co-authored-by: Oliver Hunt <oliver@<!-- -->apple.com>

---
Full diff: https://github.com/llvm/llvm-project/pull/100153.diff


1 Files Affected:

- (modified) compiler-rt/lib/ubsan/ubsan_type_hash_itanium.cpp (+1-1) 


``````````diff
diff --git a/compiler-rt/lib/ubsan/ubsan_type_hash_itanium.cpp b/compiler-rt/lib/ubsan/ubsan_type_hash_itanium.cpp
index 468a8fcd603f0..15788574dd995 100644
--- a/compiler-rt/lib/ubsan/ubsan_type_hash_itanium.cpp
+++ b/compiler-rt/lib/ubsan/ubsan_type_hash_itanium.cpp
@@ -207,7 +207,7 @@ struct VtablePrefix {
   std::type_info *TypeInfo;
 };
 VtablePrefix *getVtablePrefix(void *Vtable) {
-  Vtable = ptrauth_auth_data(Vtable, ptrauth_key_cxx_vtable_pointer, 0);
+  Vtable = ptrauth_strip(Vtable, ptrauth_key_cxx_vtable_pointer);
   VtablePrefix *Vptr = reinterpret_cast<VtablePrefix*>(Vtable);
   VtablePrefix *Prefix = Vptr - 1;
   if (!IsAccessibleMemoryRange((uptr)Prefix, sizeof(VtablePrefix)))

``````````

</details>


https://github.com/llvm/llvm-project/pull/100153