[compiler-rt] [libcxxabi] [libunwind] [runtimes][PAC] Harden unwinding when possible (#138571) (PR #143230)

[Daniil Kovalev via llvm-commits]

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@@ -1845,10 +1871,53 @@ 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  getFP() const         { return _registers.__fp; }
-  void      setFP(uint64_t value) { _registers.__fp = value; }
+  uint64_t getIP() const {
+    uint64_t value = _registers.__pc;
+#if __has_feature(ptrauth_calls)
+    // Note the value of the PC was signed to its address in the register state
+    // but everyone else expects it to be sign by the SP, so convert on return.
+    value = (uint64_t)ptrauth_auth_and_resign(
+        (void *)_registers.__pc, ptrauth_key_return_address, &_registers.__pc,
+        ptrauth_key_return_address, getSP());
+#endif
+    return value;
+  }
+  void setIP(uint64_t value) {
+#if __has_feature(ptrauth_calls)
+    // Note the value which was set should have been signed with the SP.
+    // We then resign with the slot we are being stored in to so that both SP
+    // and LR can't be spoofed at the same time.
+    value = (uint64_t)ptrauth_auth_and_resign(
+        (void *)value, ptrauth_key_return_address, getSP(),
+        ptrauth_key_return_address, &_registers.__pc);
+#endif
+    _registers.__pc = value;
+  }
+  uint64_t getFP() const { return _registers.__fp; }
+  void setFP(uint64_t value) { _registers.__fp = value; }
+
+  typedef uint64_t reg_t;
+  typedef uint64_t
+      __LIBUNWIND_PTRAUTH_RI_PDC("Registers_arm64::link_reg_t") link_reg_t;
+  void
+  loadAndAuthenticateLinkRegister(reg_t inplaceAuthedLinkRegister,
+                                  link_reg_t *referenceAuthedLinkRegister) {
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kovdan01 wrote:

Nit: probably it's worth using l-value reference instead of a pointer. We assume this being non-null, and actually each time you call this in UnwindCursor.hpp you are taking an address of a variable. L-value reference seems to be a perfect fit for this situation.

https://github.com/llvm/llvm-project/pull/143230