// Copyright 2018 The gVisor Authors. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. #include <signal.h> #include "gtest/gtest.h" #include "test/util/logging.h" #include "test/util/platform_util.h" #include "test/util/signal_util.h" #include "test/util/test_util.h" namespace gvisor { namespace testing { // Default value for the x87 FPU control word. See Intel SDM Vol 1, Ch 8.1.5 // "x87 FPU Control Word". constexpr uint16_t kX87ControlWordDefault = 0x37f; // Mask for the divide-by-zero exception. constexpr uint16_t kX87ControlWordDiv0Mask = 1 << 2; // Default value for the SSE control register (MXCSR). See Intel SDM Vol 1, Ch // 11.6.4 "Initialization of SSE/SSE3 Extensions". constexpr uint32_t kMXCSRDefault = 0x1f80; // Mask for the divide-by-zero exception. constexpr uint32_t kMXCSRDiv0Mask = 1 << 9; // Flag for a pending divide-by-zero exception. constexpr uint32_t kMXCSRDiv0Flag = 1 << 2; void inline Halt() { asm("hlt\r\n"); } void inline SetAlignmentCheck() { asm("subq $128, %%rsp\r\n" // Avoid potential red zone clobber "pushf\r\n" "pop %%rax\r\n" "or $0x40000, %%rax\r\n" "push %%rax\r\n" "popf\r\n" "addq $128, %%rsp\r\n" : : : "ax"); } void inline ClearAlignmentCheck() { asm("subq $128, %%rsp\r\n" // Avoid potential red zone clobber "pushf\r\n" "pop %%rax\r\n" "mov $0x40000, %%rbx\r\n" "not %%rbx\r\n" "and %%rbx, %%rax\r\n" "push %%rax\r\n" "popf\r\n" "addq $128, %%rsp\r\n" : : : "ax", "bx"); } void inline Int3Normal() { asm(".byte 0xcd, 0x03\r\n"); } void inline Int3Compact() { asm(".byte 0xcc\r\n"); } void InIOHelper(int width, int value) { EXPECT_EXIT( { switch (width) { case 1: asm volatile("inb %%dx, %%al" ::"d"(value) : "%eax"); break; case 2: asm volatile("inw %%dx, %%ax" ::"d"(value) : "%eax"); break; case 4: asm volatile("inl %%dx, %%eax" ::"d"(value) : "%eax"); break; default: FAIL() << "invalid input width, only 1, 2 or 4 is allowed"; } }, ::testing::KilledBySignal(SIGSEGV), ""); } TEST(ExceptionTest, Halt) { // In order to prevent the regular handler from messing with things (and // perhaps refaulting until some other signal occurs), we reset the handler to // the default action here and ensure that it dies correctly. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGSEGV, sa)); EXPECT_EXIT(Halt(), ::testing::KilledBySignal(SIGSEGV), ""); } TEST(ExceptionTest, DivideByZero) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGFPE, sa)); EXPECT_EXIT( { uint32_t remainder; uint32_t quotient; uint32_t divisor = 0; uint64_t value = 1; asm("divl 0(%2)\r\n" : "=d"(remainder), "=a"(quotient) : "r"(&divisor), "d"(value >> 32), "a"(value)); TEST_CHECK(quotient > 0); // Force dependency. }, ::testing::KilledBySignal(SIGFPE), ""); } // By default, x87 exceptions are masked and simply return a default value. TEST(ExceptionTest, X87DivideByZeroMasked) { int32_t quotient; int32_t value = 1; int32_t divisor = 0; asm("fildl %[value]\r\n" "fidivl %[divisor]\r\n" "fistpl %[quotient]\r\n" : [ quotient ] "=m"(quotient) : [ value ] "m"(value), [ divisor ] "m"(divisor)); EXPECT_EQ(quotient, INT32_MIN); } // When unmasked, division by zero raises SIGFPE. TEST(ExceptionTest, X87DivideByZeroUnmasked) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGFPE, sa)); EXPECT_EXIT( { // Clear the divide by zero exception mask. constexpr uint16_t kControlWord = kX87ControlWordDefault & ~kX87ControlWordDiv0Mask; int32_t quotient; int32_t value = 1; int32_t divisor = 0; asm volatile( "fldcw %[cw]\r\n" "fildl %[value]\r\n" "fidivl %[divisor]\r\n" "fistpl %[quotient]\r\n" : [ quotient ] "=m"(quotient) : [ cw ] "m"(kControlWord), [ value ] "m"(value), [ divisor ] "m"(divisor)); }, ::testing::KilledBySignal(SIGFPE), ""); } // Pending exceptions in the x87 status register are not clobbered by syscalls. TEST(ExceptionTest, X87StatusClobber) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGFPE, sa)); EXPECT_EXIT( { // Clear the divide by zero exception mask. constexpr uint16_t kControlWord = kX87ControlWordDefault & ~kX87ControlWordDiv0Mask; int32_t quotient; int32_t value = 1; int32_t divisor = 0; asm volatile( "fildl %[value]\r\n" "fidivl %[divisor]\r\n" // Exception is masked, so it does not occur here. "fistpl %[quotient]\r\n" // SYS_getpid placed in rax by constraint. "syscall\r\n" // Unmask exception. The syscall didn't clobber the pending // exception, so now it can be raised. // // N.B. "a floating-point exception will be generated upon execution // of the *next* floating-point instruction". "fldcw %[cw]\r\n" "fwait\r\n" : [ quotient ] "=m"(quotient) : [ value ] "m"(value), [ divisor ] "m"(divisor), "a"(SYS_getpid), [ cw ] "m"(kControlWord) : "rcx", "r11"); }, ::testing::KilledBySignal(SIGFPE), ""); } // By default, SSE exceptions are masked and simply return a default value. TEST(ExceptionTest, SSEDivideByZeroMasked) { uint32_t status; int32_t quotient; int32_t value = 1; int32_t divisor = 0; asm("cvtsi2ssl %[value], %%xmm0\r\n" "cvtsi2ssl %[divisor], %%xmm1\r\n" "divss %%xmm1, %%xmm0\r\n" "cvtss2sil %%xmm0, %[quotient]\r\n" : [ quotient ] "=r"(quotient), [ status ] "=r"(status) : [ value ] "r"(value), [ divisor ] "r"(divisor) : "xmm0", "xmm1"); EXPECT_EQ(quotient, INT32_MIN); } // When unmasked, division by zero raises SIGFPE. TEST(ExceptionTest, SSEDivideByZeroUnmasked) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGFPE, sa)); EXPECT_EXIT( { // Clear the divide by zero exception mask. constexpr uint32_t kMXCSR = kMXCSRDefault & ~kMXCSRDiv0Mask; int32_t quotient; int32_t value = 1; int32_t divisor = 0; asm volatile( "ldmxcsr %[mxcsr]\r\n" "cvtsi2ssl %[value], %%xmm0\r\n" "cvtsi2ssl %[divisor], %%xmm1\r\n" "divss %%xmm1, %%xmm0\r\n" "cvtss2sil %%xmm0, %[quotient]\r\n" : [ quotient ] "=r"(quotient) : [ mxcsr ] "m"(kMXCSR), [ value ] "r"(value), [ divisor ] "r"(divisor) : "xmm0", "xmm1"); }, ::testing::KilledBySignal(SIGFPE), ""); } // Pending exceptions in the SSE status register are not clobbered by syscalls. TEST(ExceptionTest, SSEStatusClobber) { uint32_t mxcsr; int32_t quotient; int32_t value = 1; int32_t divisor = 0; asm("cvtsi2ssl %[value], %%xmm0\r\n" "cvtsi2ssl %[divisor], %%xmm1\r\n" "divss %%xmm1, %%xmm0\r\n" // Exception is masked, so it does not occur here. "cvtss2sil %%xmm0, %[quotient]\r\n" // SYS_getpid placed in rax by constraint. "syscall\r\n" // Intel SDM Vol 1, Ch 10.2.3.1 "SIMD Floating-Point Mask and Flag Bits": // "If LDMXCSR or FXRSTOR clears a mask bit and sets the corresponding // exception flag bit, a SIMD floating-point exception will not be // generated as a result of this change. The unmasked exception will be // generated only upon the execution of the next SSE/SSE2/SSE3 instruction // that detects the unmasked exception condition." // // Though ambiguous, empirical evidence indicates that this means that // exception flags set in the status register will never cause an // exception to be raised; only a new exception condition will do so. // // Thus here we just check for the flag itself rather than trying to raise // the exception. "stmxcsr %[mxcsr]\r\n" : [ quotient ] "=r"(quotient), [ mxcsr ] "+m"(mxcsr) : [ value ] "r"(value), [ divisor ] "r"(divisor), "a"(SYS_getpid) : "xmm0", "xmm1", "rcx", "r11"); EXPECT_TRUE(mxcsr & kMXCSRDiv0Flag); } TEST(ExceptionTest, IOAccessFault) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGSEGV, sa)); InIOHelper(1, 0x0); InIOHelper(2, 0x7); InIOHelper(4, 0x6); InIOHelper(1, 0xffff); InIOHelper(2, 0xffff); InIOHelper(4, 0xfffd); } TEST(ExceptionTest, Alignment) { SetAlignmentCheck(); ClearAlignmentCheck(); } TEST(ExceptionTest, AlignmentHalt) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGSEGV, sa)); // Reported upstream. We need to ensure that bad flags are cleared even in // fault paths. Set the alignment flag and then generate an exception. EXPECT_EXIT( { SetAlignmentCheck(); Halt(); }, ::testing::KilledBySignal(SIGSEGV), ""); } TEST(ExceptionTest, AlignmentCheck) { SKIP_IF(PlatformSupportAlignmentCheck() != PlatformSupport::Allowed); // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGBUS, sa)); EXPECT_EXIT( { char array[16]; SetAlignmentCheck(); for (int i = 0; i < 8; i++) { // At least 7/8 offsets will be unaligned here. uint64_t* ptr = reinterpret_cast<uint64_t*>(&array[i]); asm("mov %0, 0(%0)\r\n" : : "r"(ptr) : "ax"); } }, ::testing::KilledBySignal(SIGBUS), ""); } TEST(ExceptionTest, Int3Normal) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGTRAP, sa)); EXPECT_EXIT(Int3Normal(), ::testing::KilledBySignal(SIGTRAP), ""); } TEST(ExceptionTest, Int3Compact) { // See above. struct sigaction sa = {}; sa.sa_handler = SIG_DFL; auto const cleanup = ASSERT_NO_ERRNO_AND_VALUE(ScopedSigaction(SIGTRAP, sa)); EXPECT_EXIT(Int3Compact(), ::testing::KilledBySignal(SIGTRAP), ""); } } // namespace testing } // namespace gvisor