Merge pull request #4689 from Sonicadvance1/disable_gcs_protection

Disable GCS in simulator and userspace

FEXCore/Source/Interface/Core/ArchHelpers/Arm64Emitter.cpp

@@ -370,6 +370,8 @@ Arm64Emitter::Arm64Emitter(FEXCore::Context::ContextImpl* ctx, void* EmissionPtr
   // Hardcode a 256-bit vector width if we are running in the simulator.
   // Allow the user to override this.
   Simulator.SetVectorLengthInBits(ForceSVEWidth() ? ForceSVEWidth() : 256);
+  // FEX doesn't support GCS.
+  Simulator.DisableGCSCheck();
 #endif
 #ifdef VIXL_DISASSEMBLER
   // Only setup the disassembler if enabled.

Source/Tools/FEXLoader/FEXLoader.cpp

@@ -270,6 +270,33 @@ void SetupCompatInput(bool enable) {
 }
 } // namespace FEX::CompatInput
 
+namespace FEX::GCS {
+  void CheckForGCS() {
+#ifndef PR_GET_SHADOW_STACK_STATUS
+#define PR_GET_SHADOW_STACK_STATUS 74
+#endif
+#ifndef PR_LOCK_SHADOW_STACK_STATUS
+#define PR_LOCK_SHADOW_STACK_STATUS 76
+#endif
+#ifndef PR_SHADOW_STACK_ENABLE
+#define PR_SHADOW_STACK_ENABLE (1ULL << 0)
+#endif
+    uint64_t ShadowStackWord {};
+    if (prctl(PR_GET_SHADOW_STACK_STATUS, &ShadowStackWord, 0, 0, 0) == -1) {
+      return;
+    }
+
+    // Kernel supports shadow stack.
+    if (ShadowStackWord & PR_SHADOW_STACK_ENABLE) {
+      // Welp.
+      ERROR_AND_DIE_FMT("Shadow stack is enabled which FEX is incompatible with!");
+    }
+
+    // Disable if we've gotten this far, to ensure guest can't try.
+    prctl(PR_LOCK_SHADOW_STACK_STATUS, ~0ULL, 0, 0, 0);
+  }
+}
+
 /**
  * @brief Get an FD from an environment variable and then unset the environment variable.
  *
@@ -314,6 +341,8 @@ int main(int argc, char** argv, char** const envp) {
     return 0;
   }
 
+  FEX::GCS::CheckForGCS();
+
   FEX::Config::LoadConfig(std::move(ArgsLoader), Program.ProgramName, envp, PortableInfo);
 
   // Reload the meta layer