Protect Windows guest red zones when emulating VRSQRTPS

src/launcher/src/configurationEditDialog.cpp

@@ -240,7 +240,7 @@ void ConfigurationEditDialog::Init(const Configuration& info) {
 	m_ui->checkBox_vulkan_validation->setChecked(info.vulkan_validation_enabled);
 	m_ui->checkBox_renderdoc_capture->setChecked(info.renderdoc_enabled);
 	m_ui->checkBox_amd_cpu->setChecked(info.amd_cpu_enabled);
-#if !defined(__linux__)
+#if defined(__APPLE__)
 	m_ui->checkBox_amd_cpu->setVisible(false);
 #endif
 #if defined(_WIN32)

src/loader/redZonePatcher.h

@@ -14,7 +14,7 @@ namespace Loader {
 struct RedZonePatchResult {
 	uint64_t function_count                           = 0;
 	uint64_t instruction_count                        = 0;
-	uint64_t red_zone_function_count                  = 0;
+	uint64_t red_zone_function_count                   = 0;
 	uint64_t memory_instruction_count                 = 0;
 	uint64_t short_memory_instruction_count           = 0;
 	uint64_t patched_memory_instruction_count         = 0;
@@ -22,14 +22,17 @@ struct RedZonePatchResult {
 	uint64_t control_flow_memory_instruction_count    = 0;
 	uint64_t unrelocatable_memory_instruction_count   = 0;
 	uint64_t indirect_red_zone_function_count         = 0;
+	uint64_t reciprocal_sqrt_instruction_count        = 0;
 };
 
 void RegisterRedZonePatchModule(void* module_ptr, uint64_t module_size, void* trampoline_area_ptr,
                                 uint64_t trampoline_area_size);
 void UnregisterRedZonePatchModule(void* module_ptr);
 
-RedZonePatchResult PatchRedZoneMemoryInstructions(uint64_t segment_addr, uint64_t segment_size,
-                                                  std::span<const uintptr_t> function_starts);
+// Analyze and protect fault sites before replacing reciprocal roots with traps.
+RedZonePatchResult PatchGuestInstructions(uint64_t segment_addr, uint64_t segment_size,
+                                          std::span<const uintptr_t> function_starts,
+                                          bool protect_memory, bool emulate_rsqrt);
 
 bool DecodeEhFrameFunctionStarts(uint64_t eh_frame_header_addr, uint64_t eh_frame_header_size,
                                  std::vector<uintptr_t>* function_starts);

src/loader/runtimeLinker.cpp

@@ -2014,9 +2014,11 @@ void RuntimeLinker::LoadProgramToMemory(Program* program) {
 	uint64_t tls_handler_size = is_shared ? 0 : Jit::SafeCall::GetSize();
 	EXIT_IF(tls_handler_size > UINT64_MAX - program->base_size_aligned);
 	program->mapped_size = program->base_size_aligned + tls_handler_size;
+	const bool emulate_rsqrt = Config::AmdCpuEnabled();
 
 #if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
-	const bool         use_red_zone_protection  = Config::RedZoneProtectionEnabled();
+	const bool         protect_memory_faults   = Config::RedZoneProtectionEnabled();
+	const bool         use_red_zone_protection = protect_memory_faults || emulate_rsqrt;
 	constexpr uint64_t RED_ZONE_TRAMPOLINE_SIZE = 8u * 1024u * 1024u;
 	if (use_red_zone_protection) {
 		EXIT_IF(RED_ZONE_TRAMPOLINE_SIZE > UINT64_MAX - program->mapped_size);
@@ -2062,9 +2064,8 @@ void RuntimeLinker::LoadProgramToMemory(Program* program) {
 		EXIT("Failed to install the required vectored exception handler\n");
 	}
 
-	// program->elf->SetBaseVAddr(program->base_vaddr);
-#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
 	std::vector<std::pair<uint64_t, uint64_t>> executable_segments;
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
 	uint64_t                                   eh_frame_header_addr = 0;
 	uint64_t                                   eh_frame_header_size = 0;
 #endif
@@ -2089,22 +2090,8 @@ void RuntimeLinker::LoadProgramToMemory(Program* program) {
 			                     mode == Common::VirtualMemory::Mode::NoAccess);
 
 			if (Common::VirtualMemory::IsExecute(mode)) {
-				if (Config::AmdCpuEnabled()) {
-					const auto reciprocal_sqrt_count =
-					    X64InstructionEmulator::PatchReciprocalSquareRoots(segment_addr,
-					                                                        segment_file_size);
-					if (reciprocal_sqrt_count != 0) {
-						LOGF("Guest VRSQRTPS emulation: %s, instructions=%" PRIu64 "\n",
-						     Common::PathToString(program->file_name.filename()).c_str(),
-						     reciprocal_sqrt_count);
-					}
-				}
 				PatchProgram(program, segment_addr, segment_memory_size);
-#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
-				if (use_red_zone_protection) {
-					executable_segments.emplace_back(segment_addr, segment_file_size);
-				}
-#endif
+				executable_segments.emplace_back(segment_addr, segment_file_size);
 			}
 
 			if (!skip_protect) {
@@ -2149,16 +2136,22 @@ void RuntimeLinker::LoadProgramToMemory(Program* program) {
 	}
 
 #if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+	std::vector<uintptr_t> function_starts;
 	if (use_red_zone_protection) {
-		std::vector<uintptr_t> function_starts;
 		if (!DecodeEhFrameFunctionStarts(eh_frame_header_addr, eh_frame_header_size,
 		                                 &function_starts)) {
 			LOGF("Windows guest red-zone patching could not decode function boundaries for %s\n",
 			     Common::PathToString(program->file_name).c_str());
 		}
-		for (const auto& [segment_addr, segment_size]: executable_segments) {
+	}
+#endif
+	for (const auto& [segment_addr, segment_size]: executable_segments) {
+		uint64_t reciprocal_sqrt_count = 0;
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+		if (use_red_zone_protection) {
 			const auto result =
-			    PatchRedZoneMemoryInstructions(segment_addr, segment_size, function_starts);
+			    PatchGuestInstructions(segment_addr, segment_size, function_starts,
+			                           protect_memory_faults, emulate_rsqrt);
 			LOGF("Windows guest red-zone patching: %s, functions=%" PRIu64 ", red_zone=%" PRIu64
 			     ", memory=%" PRIu64 ", patched=%" PRIu64 ", short=%" PRIu64 ", stack=%" PRIu64
 			     ", control=%" PRIu64 ", unrelocatable=%" PRIu64 "\n",
@@ -2168,12 +2161,20 @@ void RuntimeLinker::LoadProgramToMemory(Program* program) {
 			     result.stack_dependent_memory_instruction_count,
 			     result.control_flow_memory_instruction_count,
 			     result.unrelocatable_memory_instruction_count);
+			reciprocal_sqrt_count = result.reciprocal_sqrt_instruction_count;
+		}
+#else
+		if (emulate_rsqrt) {
+			reciprocal_sqrt_count =
+			    X64InstructionEmulator::PatchReciprocalSquareRoots(segment_addr, segment_size);
 			Common::VirtualMemory::FlushInstructionCache(segment_addr, segment_size);
 		}
-		Common::VirtualMemory::FlushInstructionCache(program->red_zone_trampoline_vaddr,
-		                                             program->red_zone_trampoline_size);
-	}
 #endif
+		if (reciprocal_sqrt_count != 0) {
+			LOGF("Guest VRSQRTPS emulation: %s, instructions=%" PRIu64 "\n",
+			     Common::PathToString(program->file_name.filename()).c_str(), reciprocal_sqrt_count);
+		}
+	}
 
 	if (!is_shared) {
 		SetupTlsHandler(program);

src/loader/x64InstructionEmulator.cpp

@@ -5,7 +5,7 @@
 #include <Zydis/Zydis.h>
 #include <bit>
 #include <cstring>
-#if KYTY_PLATFORM == KYTY_PLATFORM_LINUX && !defined(__APPLE__)
+#if !defined(__APPLE__)
 #include <emmintrin.h>
 #include <xmmintrin.h>
 #endif
@@ -424,6 +424,21 @@ struct Context {
 		                              native->R12, native->R13, native->R14, native->R15};
 		std::memcpy(gpr, registers, sizeof(gpr));
 	}
+
+	void ClearUpperYmm(uint8_t index) const {
+		if ((native->ContextFlags & CONTEXT_XSTATE) != CONTEXT_XSTATE) {
+			return;
+		}
+		DWORD64 features = 0;
+		if (!GetXStateFeaturesMask(native, &features) || (features & XSTATE_MASK_AVX) == 0) {
+			return; // An absent AVX component restores zeroes.
+		}
+		DWORD size = 0;
+		auto* ymm = static_cast<M128A*>(LocateXStateFeature(native, XSTATE_AVX, &size));
+		if (ymm != nullptr && size >= (index + 1u) * sizeof(M128A)) {
+			ymm[index] = {};
+		}
+	}
 #else
 	ucontext_t* native;
 
@@ -588,8 +603,6 @@ static bool TryEmulateMonitorxMwaitx(Context& context) {
 	return true;
 }
 
-#if KYTY_PLATFORM == KYTY_PLATFORM_LINUX
-
 static uint32_t ReciprocalSquareRoot(uint32_t bits) {
 	const uint32_t magnitude = bits & 0x7fffffffu;
 	const uint32_t exponent  = magnitude & 0x7f800000u;
@@ -658,11 +671,18 @@ static bool TryEmulateReciprocalSquareRoot(Context& context) {
 }
 
 #endif
-#endif
+
+bool IsReciprocalSquareRoot(const ZydisDecodedInstruction& instruction,
+                            const ZydisDecodedOperand* operands) {
+	return instruction.mnemonic == ZYDIS_MNEMONIC_VRSQRTPS &&
+	       instruction.encoding == ZYDIS_INSTRUCTION_ENCODING_VEX &&
+	       instruction.raw.vex.offset == 0 && operands[0].size == 128 &&
+	       operands[1].type == ZYDIS_OPERAND_TYPE_REGISTER;
+}
 
 uint64_t PatchReciprocalSquareRoots(uint64_t address, uint64_t size) {
 	uint64_t patched = 0;
-#if KYTY_PLATFORM == KYTY_PLATFORM_LINUX && !defined(__APPLE__)
+#if !defined(__APPLE__)
 	ZydisDecoder decoder {};
 	if (!ZYAN_SUCCESS(
 	        ZydisDecoderInit(&decoder, ZYDIS_MACHINE_MODE_LONG_64, ZYDIS_STACK_WIDTH_64))) {
@@ -677,12 +697,9 @@ uint64_t PatchReciprocalSquareRoots(uint64_t address, uint64_t size) {
 			++offset;
 			continue;
 		}
-		if (instruction.mnemonic == ZYDIS_MNEMONIC_VRSQRTPS &&
-		    instruction.encoding == ZYDIS_INSTRUCTION_ENCODING_VEX &&
-		    instruction.raw.vex.offset == 0 && operands[0].size == 128 &&
-		    operands[1].type == ZYDIS_OPERAND_TYPE_REGISTER) {
+		if (IsReciprocalSquareRoot(instruction, operands)) {
 			// vvvv is reserved (must be 1111b). Clear one bit to route this
-			// otherwise intact instruction through the existing SIGILL emulator.
+			// otherwise intact instruction through the illegal-instruction emulator.
 			code[instruction.raw.vex.size - 1] &= ~0x08u;
 			++patched;
 		}
@@ -704,10 +721,10 @@ bool TryEmulate(void* native_context) {
 	Context context {static_cast<PCONTEXT>(native_context)};
 #else
 	Context context {static_cast<ucontext_t*>(native_context)};
+#endif
 	if (TryEmulateReciprocalSquareRoot(context)) {
 		return true;
 	}
-#endif
 	return TryEmulateMonitorxMwaitx(context) || TryEmulateSse4a(context) ||
 	       TryEmulateShaNi(context);
 #else

src/loader/x64InstructionEmulator.h

@@ -1,10 +1,13 @@
 #ifndef KYTY_LOADER_X64_INSTRUCTION_EMULATOR_H_
 #define KYTY_LOADER_X64_INSTRUCTION_EMULATOR_H_
 
+#include <Zydis/DecoderTypes.h>
 #include <cstdint>
 
 namespace Loader::X64InstructionEmulator {
 
+[[nodiscard]] bool IsReciprocalSquareRoot(const ZydisDecodedInstruction& instruction,
+                                         const ZydisDecodedOperand* operands);
 uint64_t           PatchReciprocalSquareRoots(uint64_t address, uint64_t size);
 [[nodiscard]] bool TryEmulate(void* native_context);
 

src/main.cpp

@@ -56,7 +56,7 @@ static void PrintUsage() {
 	    "  --gpu <index>                        Vulkan physical device index. Default: auto.\n");
 	::printf("  --fullscreen                         Run in borderless desktop fullscreen.\n");
 	::printf("  --vr                                 Enable the virtual VR headset.\n");
-	::printf("  --amd-cpu                            Apply AMD CPU instruction patches (Linux).\n");
+	::printf("  --amd-cpu                            Apply AMD CPU instruction patches.\n");
 	::printf("  --vblank-frequency <num>             Virtual vblank frequency. Default: 60.\n");
 	::printf("  --console-language <0-29>            Console language. Default: 1 (English US).\n");
 	::printf("  --vulkan-validation <true|false>     Enable Vulkan validation.\n");

tests/VirtualMemoryAllocationTests.cpp

@@ -24,13 +24,16 @@
 #include <string>
 #include <vector>
 
-#if defined(__linux__)
+#if defined(__linux__) || KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
 #include <csignal>
 #include <immintrin.h>
+#include <xbyak/xbyak.h>
+#endif
+
+#if defined(__linux__)
 #include <sys/uio.h>
 #include <ucontext.h>
 #include <unistd.h>
-#include <xbyak/xbyak.h>
 #endif
 
 #if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
@@ -217,10 +220,8 @@ void TestWindowsGuestRedZoneStaticPatcher() {
 	                                   reinterpret_cast<void*>(mapping + CODE_SIZE),
 	                                   TRAMPOLINE_SIZE);
 	const std::array<uintptr_t, 1> function_starts = {static_cast<uintptr_t>(mapping)};
-	const auto result = Loader::PatchRedZoneMemoryInstructions(
-	    mapping, code.size(), function_starts);
-	Check(test, Common::VirtualMemory::FlushInstructionCache(mapping, CODE_SIZE + TRAMPOLINE_SIZE),
-	      "failed to flush patched test code");
+	const auto result = Loader::PatchGuestInstructions(
+	    mapping, code.size(), function_starts, true, false);
 	const bool patched_preserved = function(static_cast<const uint64_t*>(g_red_zone_fault_page)) == 1;
 
 	Loader::UnregisterRedZonePatchModule(reinterpret_cast<void*>(mapping));
@@ -2546,55 +2547,93 @@ void TestModuleRelocationUsesWritableHostMapping() {
 	std::printf("[host]    %-48s ok\n", test);
 }
 
-#if defined(__linux__)
+#if defined(__linux__) || KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
 volatile sig_atomic_t g_rsqrt_traps = 0;
 
-void ReciprocalSquareRootHandler(int, siginfo_t*, void* context) {
+bool EmulateReciprocalSquareRootContext(void* context) {
 	const auto host_mxcsr = _mm_getcsr();
 	_mm_setcsr(0x7fe1); // Exercise the handler under a distinct rounding mode and raised flags.
-	if (!Loader::X64InstructionEmulator::TryEmulate(context)) {
+	const bool emulated        = Loader::X64InstructionEmulator::TryEmulate(context);
+	const bool preserved_mxcsr = _mm_getcsr() == 0x7fe1;
+	_mm_setcsr(host_mxcsr);
+	if (!emulated || !preserved_mxcsr) {
+		return false;
+	}
+	g_rsqrt_traps = g_rsqrt_traps + 1;
+	return true;
+}
+
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+LONG CALLBACK ReciprocalSquareRootHandler(EXCEPTION_POINTERS* exception) {
+	if (exception->ExceptionRecord->ExceptionCode != EXCEPTION_ILLEGAL_INSTRUCTION ||
+	    !EmulateReciprocalSquareRootContext(exception->ContextRecord)) {
+		return EXCEPTION_CONTINUE_SEARCH;
+	}
+	return EXCEPTION_CONTINUE_EXECUTION;
+}
+#else
+void ReciprocalSquareRootHandler(int, siginfo_t*, void* context) {
+	if (!EmulateReciprocalSquareRootContext(context)) {
 		_exit(190);
 	}
-	if (_mm_getcsr() != 0x7fe1) {
-		_exit(191);
-	}
-	_mm_setcsr(host_mxcsr);
-	g_rsqrt_traps = g_rsqrt_traps + 1;
 }
+#endif
 
 void TestPackedReciprocalSquareRoot() {
 	const char* test = "PackedReciprocalSquareRoot";
 	constexpr uint64_t code_size = 0x4000;
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+	constexpr uint64_t allocation_size = code_size * 2;
+#else
+	constexpr uint64_t allocation_size = code_size;
+#endif
 	const auto mapping = Libs::LibKernel::Memory::AllocateProgramMemory(
-	    0x902000000, code_size, Common::VirtualMemory::Mode::ExecuteReadWrite, "rsqrt_test");
+	    0x902000000, allocation_size, Common::VirtualMemory::Mode::ExecuteReadWrite, "rsqrt_test");
 	Check(test, mapping != 0, "failed to allocate instruction test code");
 	struct RestoreState {
 		uint64_t mapping;
 		uint64_t size;
 		uint32_t mxcsr;
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+		void* handler = nullptr;
+#else
 		struct sigaction previous {};
 		bool installed = false;
+#endif
 		~RestoreState() {
 			_mm_setcsr(mxcsr);
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+			if (handler != nullptr) {
+				RemoveVectoredExceptionHandler(handler);
+			}
+			Loader::UnregisterRedZonePatchModule(reinterpret_cast<void*>(mapping));
+#else
 			if (installed) {
 				sigaction(SIGILL, &previous, nullptr);
 			}
+#endif
 			Libs::LibKernel::Memory::FreeGuestMemory(mapping, size);
 		}
-	} restore {mapping, code_size, _mm_getcsr()};
+	} restore {mapping, allocation_size, _mm_getcsr()};
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+	restore.handler = AddVectoredExceptionHandler(1, ReciprocalSquareRootHandler);
+	Check(test, restore.handler != nullptr, "failed to install instruction handler");
+#else
 	struct sigaction action {};
 	action.sa_sigaction = ReciprocalSquareRootHandler;
 	action.sa_flags = SA_SIGINFO;
 	sigemptyset(&action.sa_mask);
 	restore.installed = sigaction(SIGILL, &action, &restore.previous) == 0;
 	Check(test, restore.installed, "failed to install instruction handler");
+#endif
 	using GuestFunction = void(KYTY_SYSV_ABI*)(const uint32_t*, uint32_t*);
 	const auto function = reinterpret_cast<GuestFunction>(mapping);
 	const auto refine = [](float estimate) {
 		return (estimate * 0.5f) * std::fma(-estimate, estimate, 3.0f);
 	};
+	constexpr uint64_t red_zone_sentinel = 0x1122334455667788ull;
 	std::array<uint32_t, 16> input {};
-	std::array<uint32_t, 16> output {};
+	std::array<uint32_t, 48> output {};
 	input.fill(0x3f800000);
 	for (const auto registers: {std::array {2, 1}, std::array {10, 9}, std::array {1, 1}}) {
 		const auto destination = registers[0];
@@ -2613,16 +2652,55 @@ void TestPackedReciprocalSquareRoot() {
 		if (destination != source) {
 			code.vmovups(Xbyak::Ymm(destination), code.ptr[code.rdi + 32]);
 		}
+		for (uint32_t offset = 8; offset <= 128; offset += 8) {
+			code.mov(code.rax, red_zone_sentinel ^ offset);
+			code.mov(code.qword[code.rsp - offset], code.rax);
+		}
 		code.vrsqrtps(Xbyak::Xmm(destination), Xbyak::Xmm(source));
+		for (uint32_t offset = 8; offset <= 128; offset += 8) {
+			code.mov(code.rax, code.qword[code.rsp - offset]);
+			code.mov(code.qword[code.rsi + 64 + offset - 8], code.rax);
+		}
 		code.vmovups(code.ptr[code.rsi], Xbyak::Ymm(destination));
 		code.vmovups(code.ptr[code.rsi + 32], Xbyak::Ymm(source));
 		code.vzeroupper();
 		code.ret();
+#if defined(__linux__)
 		const std::vector<uint8_t> original(code.getCode(), code.getCurr());
+#endif
+		Check(test, Common::VirtualMemory::FlushInstructionCache(mapping, code.getSize()),
+		      "failed to flush generated instruction test code");
 		function(input.data(), output.data());
 		const float native = std::bit_cast<float>(output[0]);
+		const auto red_zone_intact = [&] {
+			for (uint32_t offset = 8; offset <= 128; offset += 8) {
+				const auto index = 16 + (offset - 8) / sizeof(uint32_t);
+				const auto value = static_cast<uint64_t>(output[index]) |
+				                   (static_cast<uint64_t>(output[index + 1]) << 32);
+				if (value != (red_zone_sentinel ^ offset)) {
+					return false;
+				}
+			}
+			return true;
+		};
+		Check(test, red_zone_intact(), "native instruction corrupted the guest red zone");
 		Check(test, std::isfinite(native) && std::abs(native - std::bit_cast<float>(expected)) < 0.001f,
 		      "native reciprocal root is outside its error bound");
+#if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
+		Loader::RegisterRedZonePatchModule(reinterpret_cast<void*>(mapping), code_size,
+		                                   reinterpret_cast<void*>(mapping + code_size), code_size);
+		const std::array<uintptr_t, 1> function_starts {mapping};
+		// The extended-register case also relocates ordinary memory accesses while
+		// red-zone data is live, exercising both enabled patchers in one function.
+		const bool protect_memory = source == 9;
+		const auto patched = Loader::PatchGuestInstructions(
+		    mapping, code.getSize(), function_starts, protect_memory, true);
+		Check(test, patched.reciprocal_sqrt_instruction_count == 1 &&
+		                patched.unrelocatable_memory_instruction_count == 0 &&
+		                (protect_memory ? patched.patched_memory_instruction_count > 0
+		                                : patched.patched_memory_instruction_count == 0),
+		      "instruction pass lost reciprocal root or memory patch coverage");
+#else
 		Check(test, Loader::X64InstructionEmulator::PatchReciprocalSquareRoots(mapping, code.getSize()) == 1,
 		      "instruction pass did not patch exactly one packed reciprocal root");
 		const auto* patched = reinterpret_cast<const uint8_t*>(mapping);
@@ -2631,11 +2709,18 @@ void TestPackedReciprocalSquareRoot() {
 			changed += original[i] != patched[i];
 		}
 		Check(test, changed == 1, "instruction pass changed unrelated code bytes");
-		Common::VirtualMemory::FlushInstructionCache(mapping, code.getSize());
+		Check(test, Common::VirtualMemory::FlushInstructionCache(mapping, code.getSize()),
+		      "failed to flush patched instruction test code");
+#endif
 		const auto before = g_rsqrt_traps;
 		function(input.data(), output.data());
 		Check(test, g_rsqrt_traps == before + 1, "patched instruction did not execute its handler");
+		Check(test, red_zone_intact(), "patched instruction corrupted the guest red zone");
 		Check(test, output[0] == expected, "patched instruction read or wrote the wrong register");
+		if (destination != source) {
+			Check(test, std::equal(input.begin(), input.begin() + 4, output.begin() + 8),
+			      "source lower XMM lanes were corrupted");
+		}
 		if (source != 9) {
 			Check(test, refine(refine(std::bit_cast<float>(output[0]))) == 1.0f,
 			      "identity quaternion normalization drifted below one");
@@ -2668,6 +2753,7 @@ void TestPackedReciprocalSquareRoot() {
 				function(input.data(), output.data());
 				const auto result_mxcsr = _mm_getcsr();
 				_mm_setcsr(restore.mxcsr);
+				Check(test, red_zone_intact(), "special-value trap corrupted the guest red zone");
 				Check(test, result_mxcsr == mxcsr, "instruction changed MXCSR controls or exception flags");
 				Check(test, std::equal(output.begin(), output.begin() + 4, values.begin() + 4),
 				      "special values or round-independent reciprocal roots differ from ISA semantics");
@@ -2675,6 +2761,7 @@ void TestPackedReciprocalSquareRoot() {
 		}
 		input.fill(0x3f800000);
 	}
+#if defined(__linux__)
 	std::array<uint8_t, 16> unknown {0x0f, 0x0b};
 	ucontext_t context {};
 	context.uc_mcontext.gregs[REG_RIP] = reinterpret_cast<greg_t>(unknown.data());
@@ -2708,6 +2795,7 @@ void TestPackedReciprocalSquareRoot() {
 	Check(test, std::equal(sha_expected.begin(), sha_expected.end(), fpstate._xmm[8].element),
 	      "SHA emulation lost its memory operand or extended destination register");
 	emulate({0x0f, 0x01, 0xfa}, 3); // monitorx
+#endif
 	std::printf("[host]    %-48s ok\n", test);
 }
 #endif
@@ -2716,7 +2804,7 @@ void TestPackedReciprocalSquareRoot() {
 
 int main(int argc, char** argv) {
 	InitSubsystems();
-#if defined(__linux__)
+#if defined(__linux__) || KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
 	if (argc == 2 && std::strcmp(argv[1], "--rsqrt-only") == 0) {
 		RunTest(TestPackedReciprocalSquareRoot);
 		return g_failed_tests == 0 ? 0 : 1;
@@ -2727,7 +2815,7 @@ int main(int argc, char** argv) {
 		return g_failed_tests == 0 ? 0 : 1;
 	}
 
-#if defined(__linux__)
+#if defined(__linux__) || KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
 	RunTest(TestPackedReciprocalSquareRoot);
 #endif
 	RunTest(TestWindowsGuestRedZoneStaticPatcher);