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

[Daniil Kovalev via llvm-commits]

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@@ -126,6 +130,36 @@ _LIBUNWIND_HIDDEN int __unw_set_reg(unw_cursor_t *cursor, unw_regnum_t regNum,
       // First, get the FDE for the old location and then update it.
       co->getInfo(&info);
       co->setInfoBasedOnIPRegister(false);
+
+#if __has_feature(ptrauth_calls)
+      // It is only valid to set the IP within the current function.
+      // This is important for ptrauth, otherwise the IP cannot be correctly
+      // signed.
+      unw_word_t stripped_value =
+          (unw_word_t)ptrauth_strip((void *)value, ptrauth_key_return_address);
+      (void)stripped_value;
+      assert(stripped_value >= info.start_ip && stripped_value <= info.end_ip);
+#endif
+
+      pint_t sp = (pint_t)co->getReg(UNW_REG_SP);
+
+#if __has_feature(ptrauth_calls)
+      {
+        // PC should have been signed with the sp, so we verify that
+        // roundtripping does not fail.
+        pint_t pc = (pint_t)co->getReg(UNW_REG_IP);
+        if (ptrauth_auth_and_resign((void *)pc, ptrauth_key_return_address, sp,
+                                    ptrauth_key_return_address,
+                                    sp) != (void *)pc) {
+          _LIBUNWIND_LOG("Bad unwind through arm64e (0x%llX, 0x%llX)->0x%llX\n",
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kovdan01 wrote:

I believe that this check would be cross-platform and will do the trick for ELF platforms as well, so it's probably worth to re-phrase this and avoid arm64e term but say something in generic pauth terms.

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