[compiler-rt] [sanitizer] Fix prctl interceptor causing PAC authentication failure (PR #153081)

[Peter Collingbourne via llvm-commits]

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@@ -1285,7 +1285,33 @@ INTERCEPTOR(int, puts, char *s) {
 #endif
 
 #if SANITIZER_INTERCEPT_PRCTL
-INTERCEPTOR(int, prctl, int option, unsigned long arg2, unsigned long arg3,
+
+#if defined(__aarch64__)
+// https://llvm.org/docs/PointerAuth.html
+// AArch64 is currently the only architecture with full PAC support.
+// Avoid adding PAC instructions to prevent crashes caused by
+// prctl(PR_PAC_RESET_KEYS, ...). Since PR_PAC_RESET_KEYS resets the
+// authentication key, using the old key afterward will lead to a crash.
+
+#if defined(__ARM_FEATURE_BTI_DEFAULT)
+# define BRANCH_PROTECTION_ATTRIBUTE \
+    __attribute__((target("branch-protection=bti")))
+#else
+# define BRANCH_PROTECTION_ATTRIBUTE \
+    __attribute__((target("branch-protection=none")))
+#endif
+
+#define PRCTL_INTERCEPTOR(ret_type, func, ...)                  \
+  DEFINE_REAL(ret_type, func, __VA_ARGS__)                      \
+  DECLARE_WRAPPER(ret_type, func, __VA_ARGS__)                  \
+  extern "C" INTERCEPTOR_ATTRIBUTE BRANCH_PROTECTION_ATTRIBUTE  \
+      ret_type WRAP(func)(__VA_ARGS__)
+
+#else
+#define PRCTL_INTERCEPTOR INTERCEPTOR
+#endif
+
+PRCTL_INTERCEPTOR(int, prctl, int option, unsigned long arg2, unsigned long arg3,
             unsigned long arg4, unsigned long arg5) {
----------------
pcc wrote:

nit: reformat

https://github.com/llvm/llvm-project/pull/153081