[libunwind] [libunwind][AArch64] Protect PC within libunwind's context. (PR #113368)

[Anton Korobeynikov via cfe-commits]

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@@ -1845,8 +1884,14 @@ class _LIBUNWIND_HIDDEN Registers_arm64 {
 
   uint64_t  getSP() const         { return _registers.__sp; }
   void      setSP(uint64_t value) { _registers.__sp = value; }
-  uint64_t  getIP() const         { return _registers.__pc; }
-  void      setIP(uint64_t value) { _registers.__pc = value; }
+  uint64_t getIP() const { return auth(_registers.__pc, getAuthSalt()); }
+  void setIP(uint64_t value) {
+    // First authenticate the current value of the IP to ensure the context
+    // is still valid. This also ensure the setIP can't be used for signing
+    // arbitrary values.
+    auth(_registers.__pc, getAuthSalt());
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asl wrote:

Since we're already having support for pointer authentication in frontend, I think it would make sense to use pauth builtins (e.g. `__builtin_ptrauth_auth_and_resign`). Then backend will do necessary things depending on the target features (e.g. if FPAC is enabled)

https://github.com/llvm/llvm-project/pull/113368