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// 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 <string.h>
#include <sys/mman.h>
#include "gtest/gtest.h"
#include "absl/base/macros.h"
#include "test/util/memory_util.h"
#include "test/util/platform_util.h"
#include "test/util/posix_error.h"
#include "test/util/test_util.h"
#ifndef __x86_64__
#error "This test is x86-64 specific."
#endif
namespace gvisor {
namespace testing {
namespace {
constexpr char kInt3 = '\xcc';
constexpr char kInt80[2] = {'\xcd', '\x80'};
constexpr char kSyscall[2] = {'\x0f', '\x05'};
constexpr char kSysenter[2] = {'\x0f', '\x34'};
void ExitGroup32(const char instruction[2], int code) {
const Mapping m = ASSERT_NO_ERRNO_AND_VALUE(
Mmap(nullptr, kPageSize, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_32BIT, -1, 0));
// Fill with INT 3 in case we execute too far.
memset(m.ptr(), kInt3, m.len());
// Copy in the actual instruction.
memcpy(m.ptr(), instruction, 2);
// We're playing *extremely* fast-and-loose with the various syscall ABIs
// here, which we can more-or-less get away with since exit_group doesn't
// return.
//
// SYSENTER expects the user stack in (%ebp) and arg6 in 0(%ebp). The kernel
// will unconditionally dereference %ebp for arg6, so we must pass a valid
// address or it will return EFAULT.
//
// SYSENTER also unconditionally returns to thread_info->sysenter_return which
// is ostensibly a stub in the 32-bit VDSO. But a 64-bit binary doesn't have
// the 32-bit VDSO mapped, so sysenter_return will simply be the value
// inherited from the most recent 32-bit ancestor, or NULL if there is none.
// As a result, return would not return from SYSENTER.
asm volatile(
"movl $252, %%eax\n" // exit_group
"movl %[code], %%ebx\n" // code
"movl %%edx, %%ebp\n" // SYSENTER: user stack (use IP as a valid addr)
"leaq -20(%%rsp), %%rsp\n"
"movl $0x2b, 16(%%rsp)\n" // SS = CPL3 data segment
"movl $0,12(%%rsp)\n" // ESP = nullptr (unused)
"movl $0, 8(%%rsp)\n" // EFLAGS
"movl $0x23, 4(%%rsp)\n" // CS = CPL3 32-bit code segment
"movl %%edx, 0(%%rsp)\n" // EIP
"iretl\n"
"int $3\n"
:
: [ code ] "m"(code), [ ip ] "d"(m.ptr())
: "rax", "rbx", "rsp");
}
constexpr int kExitCode = 42;
TEST(Syscall32Bit, Int80) {
switch (PlatformSupport32Bit()) {
case PlatformSupport::NotSupported:
break;
case PlatformSupport::Segfault:
EXPECT_EXIT(ExitGroup32(kInt80, kExitCode),
::testing::KilledBySignal(SIGSEGV), "");
break;
case PlatformSupport::Ignored:
// Since the call is ignored, we'll hit the int3 trap.
EXPECT_EXIT(ExitGroup32(kInt80, kExitCode),
::testing::KilledBySignal(SIGTRAP), "");
break;
case PlatformSupport::Allowed:
EXPECT_EXIT(ExitGroup32(kInt80, kExitCode), ::testing::ExitedWithCode(42),
"");
break;
}
}
TEST(Syscall32Bit, Sysenter) {
if (PlatformSupport32Bit() == PlatformSupport::Allowed &&
GetCPUVendor() == CPUVendor::kAMD) {
// SYSENTER is an illegal instruction in compatibility mode on AMD.
EXPECT_EXIT(ExitGroup32(kSysenter, kExitCode),
::testing::KilledBySignal(SIGILL), "");
return;
}
switch (PlatformSupport32Bit()) {
case PlatformSupport::NotSupported:
break;
case PlatformSupport::Segfault:
EXPECT_EXIT(ExitGroup32(kSysenter, kExitCode),
::testing::KilledBySignal(SIGSEGV), "");
break;
case PlatformSupport::Ignored:
// See above, except expected code is SIGSEGV.
EXPECT_EXIT(ExitGroup32(kSysenter, kExitCode),
::testing::KilledBySignal(SIGSEGV), "");
break;
case PlatformSupport::Allowed:
EXPECT_EXIT(ExitGroup32(kSysenter, kExitCode),
::testing::ExitedWithCode(42), "");
break;
}
}
TEST(Syscall32Bit, Syscall) {
if (PlatformSupport32Bit() == PlatformSupport::Allowed &&
GetCPUVendor() == CPUVendor::kIntel) {
// SYSCALL is an illegal instruction in compatibility mode on Intel.
EXPECT_EXIT(ExitGroup32(kSyscall, kExitCode),
::testing::KilledBySignal(SIGILL), "");
return;
}
switch (PlatformSupport32Bit()) {
case PlatformSupport::NotSupported:
break;
case PlatformSupport::Segfault:
EXPECT_EXIT(ExitGroup32(kSyscall, kExitCode),
::testing::KilledBySignal(SIGSEGV), "");
break;
case PlatformSupport::Ignored:
// See above.
EXPECT_EXIT(ExitGroup32(kSyscall, kExitCode),
::testing::KilledBySignal(SIGILL), "");
break;
case PlatformSupport::Allowed:
EXPECT_EXIT(ExitGroup32(kSyscall, kExitCode),
::testing::ExitedWithCode(42), "");
break;
}
}
// Far call code called below.
//
// Input stack layout:
//
// %esp+12 lcall segment
// %esp+8 lcall address offset
// %esp+0 return address
//
// The lcall will enter compatibility mode and jump to the call address (the
// address of the lret). The lret will return to 64-bit mode at the retq, which
// will return to the external caller of this function.
//
// Since this enters compatibility mode, it must be mapped in a 32-bit region of
// address space and have a 32-bit stack pointer.
constexpr char kFarCall[] = {
'\x67', '\xff', '\x5c', '\x24', '\x08', // lcall *8(%esp)
'\xc3', // retq
'\xcb', // lret
};
void FarCall32() {
const Mapping m = ASSERT_NO_ERRNO_AND_VALUE(
Mmap(nullptr, kPageSize, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS | MAP_32BIT, -1, 0));
// Fill with INT 3 in case we execute too far.
memset(m.ptr(), kInt3, m.len());
// 32-bit code.
memcpy(m.ptr(), kFarCall, sizeof(kFarCall));
// Use the end of the code page as its stack.
uintptr_t stack = m.endaddr();
uintptr_t lcall = m.addr();
uintptr_t lret = m.addr() + sizeof(kFarCall) - 1;
// N.B. We must save and restore RSP manually. GCC can do so automatically
// with an "rsp" clobber, but clang cannot.
asm volatile(
// Place the address of lret (%edx) and the 32-bit code segment (0x23) on
// the 32-bit stack for lcall.
"subl $0x8, %%ecx\n"
"movl $0x23, 4(%%ecx)\n"
"movl %%edx, 0(%%ecx)\n"
// Save the current stack and switch to 32-bit stack.
"pushq %%rbp\n"
"movq %%rsp, %%rbp\n"
"movq %%rcx, %%rsp\n"
// Run the lcall code.
"callq *%%rbx\n"
// Restore the old stack.
"leaveq\n"
: "+c"(stack)
: "b"(lcall), "d"(lret));
}
TEST(Call32Bit, Disallowed) {
switch (PlatformSupport32Bit()) {
case PlatformSupport::NotSupported:
break;
case PlatformSupport::Segfault:
EXPECT_EXIT(FarCall32(), ::testing::KilledBySignal(SIGSEGV), "");
break;
case PlatformSupport::Ignored:
ABSL_FALLTHROUGH_INTENDED;
case PlatformSupport::Allowed:
// Shouldn't crash.
FarCall32();
}
}
} // namespace
} // namespace testing
} // namespace gvisor
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