[compiler-rt] Normalize ptrauth handling in sanitizer runtime (PR #100483)

[Anton Korobeynikov via llvm-commits]

https://github.com/asl created https://github.com/llvm/llvm-project/pull/100483

 1. Include ptrauth.h if ptrauth_intrinsics language feature is specified (per ptrauth spec, this is what enables ptrauh.h usage)
 2. For PAC-RET fallback implement two changes:
   - Switch to macro, so we can ignore key argument
   - Ensure the unsigned value is erased from LR, so the possibility of gadget reuse is reduced.

Fixes #100467

>From e0df857da214737ab6383611ee6a57eb60190a7e Mon Sep 17 00:00:00 2001
From: Anton Korobeynikov <anton at korobeynikov.info>
Date: Wed, 24 Jul 2024 16:09:47 -0700
Subject: [PATCH] Normalize ptrauth handling in sanitizer runtime:  1. Include
 ptrauth.h if ptrauth_intrinsics language feature is specified     (per
 ptrauth spec, this is what enables ptrauh.h usage)  2. For PAC-RET fallback
 implement two changes:    - Switch to macro, so we can ignore key argument   
 - Ensure the unsigned value is erased from LR, so the      possibility of
 gadget reuse is reduced.

Fixes #100467
---
 .../lib/sanitizer_common/sanitizer_ptrauth.h  | 34 ++++++++++---------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_ptrauth.h b/compiler-rt/lib/sanitizer_common/sanitizer_ptrauth.h
index 5200354694851..d228dd33cf938 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_ptrauth.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_ptrauth.h
@@ -9,24 +9,26 @@
 #ifndef SANITIZER_PTRAUTH_H
 #define SANITIZER_PTRAUTH_H
 
-#if __has_feature(ptrauth_calls)
+#if __has_feature(ptrauth_intrinsics)
 #include <ptrauth.h>
 #elif defined(__ARM_FEATURE_PAC_DEFAULT) && !defined(__APPLE__)
-inline unsigned long ptrauth_strip(void* __value, unsigned int __key) {
-  // On the stack the link register is protected with Pointer
-  // Authentication Code when compiled with -mbranch-protection.
-  // Let's stripping the PAC unconditionally because xpaclri is in
-  // the NOP space so will do nothing when it is not enabled or not available.
-  unsigned long ret;
-  asm volatile(
-      "mov x30, %1\n\t"
-      "hint #7\n\t"  // xpaclri
-      "mov %0, x30\n\t"
-      : "=r"(ret)
-      : "r"(__value)
-      : "x30");
-  return ret;
-}
+// On the stack the link register is protected with Pointer
+// Authentication Code when compiled with -mbranch-protection.
+// Let's stripping the PAC unconditionally because xpaclri is in
+// the NOP space so will do nothing when it is not enabled or not available.
+#define ptrauth_strip(__value, __key)     \
+  ({                                      \
+      unsigned long ret;                  \
+      asm volatile(                       \
+        "mov x30, %1\n\t"                 \
+        "hint #7\n\t"                     \
+        "mov %0, x30\n\t"                 \
+        "mov x30, xzr\n\t"                \
+        : "=r"(ret)                       \
+        : "r"(__value)                    \
+        : "x30");                         \
+      ret;                                \
+  })
 #define ptrauth_auth_data(__value, __old_key, __old_data) __value
 #define ptrauth_string_discriminator(__string) ((int)0)
 #else