visor/pkg/sentry/platform/systrap/subprocess_amd64.go

// 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.

//go:build amd64
// +build amd64

package systrap

import (
	"fmt"
	"strings"

	"golang.org/x/sys/unix"
	"gvisor.dev/gvisor/pkg/abi/linux"
	"gvisor.dev/gvisor/pkg/hostarch"
	"gvisor.dev/gvisor/pkg/hostsyscall"
	"gvisor.dev/gvisor/pkg/seccomp"
	"gvisor.dev/gvisor/pkg/sentry/arch"
	"gvisor.dev/gvisor/pkg/sentry/platform/systrap/sysmsg"
)

const (
	// initRegsRipAdjustment is the size of the syscall instruction.
	initRegsRipAdjustment = 2
)

// resetSysemuRegs sets up emulation registers.
//
// This should be called prior to calling sysemu.
func (s *subprocess) resetSysemuRegs(regs *arch.Registers) {
	regs.Cs = s.sysmsgInitRegs.Cs
	regs.Ss = s.sysmsgInitRegs.Ss
	regs.Ds = s.sysmsgInitRegs.Ds
	regs.Es = s.sysmsgInitRegs.Es
	regs.Fs = s.sysmsgInitRegs.Fs
	regs.Gs = s.sysmsgInitRegs.Gs
}

// createSyscallRegs sets up syscall registers.
//
// This should be called to generate registers for a system call.
func createSyscallRegs(initRegs *arch.Registers, sysno uintptr, args ...arch.SyscallArgument) arch.Registers {
	// Copy initial registers.
	regs := *initRegs

	// Set our syscall number.
	regs.Rax = uint64(sysno)
	if len(args) >= 1 {
		regs.Rdi = args[0].Uint64()
	}
	if len(args) >= 2 {
		regs.Rsi = args[1].Uint64()
	}
	if len(args) >= 3 {
		regs.Rdx = args[2].Uint64()
	}
	if len(args) >= 4 {
		regs.R10 = args[3].Uint64()
	}
	if len(args) >= 5 {
		regs.R8 = args[4].Uint64()
	}
	if len(args) >= 6 {
		regs.R9 = args[5].Uint64()
	}

	return regs
}

// updateSyscallRegs updates registers after finishing sysemu.
func updateSyscallRegs(regs *arch.Registers) {
	// Ptrace puts -ENOSYS in rax on syscall-enter-stop.
	regs.Rax = regs.Orig_rax
}

// syscallReturnValue extracts a sensible return from registers.
func syscallReturnValue(regs *arch.Registers) (uintptr, error) {
	rval := int64(regs.Rax)
	if rval < 0 {
		return 0, unix.Errno(-rval)
	}
	return uintptr(rval), nil
}

func dumpRegs(regs *arch.Registers) string {
	var m strings.Builder

	fmt.Fprintf(&m, "Registers:\n")
	fmt.Fprintf(&m, "\tR15\t = %016x\n", regs.R15)
	fmt.Fprintf(&m, "\tR14\t = %016x\n", regs.R14)
	fmt.Fprintf(&m, "\tR13\t = %016x\n", regs.R13)
	fmt.Fprintf(&m, "\tR12\t = %016x\n", regs.R12)
	fmt.Fprintf(&m, "\tRbp\t = %016x\n", regs.Rbp)
	fmt.Fprintf(&m, "\tRbx\t = %016x\n", regs.Rbx)
	fmt.Fprintf(&m, "\tR11\t = %016x\n", regs.R11)
	fmt.Fprintf(&m, "\tR10\t = %016x\n", regs.R10)
	fmt.Fprintf(&m, "\tR9\t = %016x\n", regs.R9)
	fmt.Fprintf(&m, "\tR8\t = %016x\n", regs.R8)
	fmt.Fprintf(&m, "\tRax\t = %016x\n", regs.Rax)
	fmt.Fprintf(&m, "\tRcx\t = %016x\n", regs.Rcx)
	fmt.Fprintf(&m, "\tRdx\t = %016x\n", regs.Rdx)
	fmt.Fprintf(&m, "\tRsi\t = %016x\n", regs.Rsi)
	fmt.Fprintf(&m, "\tRdi\t = %016x\n", regs.Rdi)
	fmt.Fprintf(&m, "\tOrig_rax = %016x\n", regs.Orig_rax)
	fmt.Fprintf(&m, "\tRip\t = %016x\n", regs.Rip)
	fmt.Fprintf(&m, "\tCs\t = %016x\n", regs.Cs)
	fmt.Fprintf(&m, "\tEflags\t = %016x\n", regs.Eflags)
	fmt.Fprintf(&m, "\tRsp\t = %016x\n", regs.Rsp)
	fmt.Fprintf(&m, "\tSs\t = %016x\n", regs.Ss)
	fmt.Fprintf(&m, "\tFs_base\t = %016x\n", regs.Fs_base)
	fmt.Fprintf(&m, "\tGs_base\t = %016x\n", regs.Gs_base)
	fmt.Fprintf(&m, "\tDs\t = %016x\n", regs.Ds)
	fmt.Fprintf(&m, "\tEs\t = %016x\n", regs.Es)
	fmt.Fprintf(&m, "\tFs\t = %016x\n", regs.Fs)
	fmt.Fprintf(&m, "\tGs\t = %016x\n", regs.Gs)

	return m.String()
}

// adjustInitregsRip adjust the current register RIP value to
// be just before the system call instruction execution
func (t *thread) adjustInitRegsRip() {
	t.initRegs.Rip -= initRegsRipAdjustment
}

// Pass the expected PPID to the child via R15 when creating stub process.
func initChildProcessPPID(initregs *arch.Registers, ppid int32) {
	// Rbx has to be set to 1 when creating stub process.
	initregs.Rbx = _NEW_STUB
}

// patchSignalInfo patches the signal info to account for hitting the seccomp
// filters from vsyscall emulation, specified below. We allow for SIGSYS as a
// synchronous trap, but patch the structure to appear like a SIGSEGV with the
// Rip as the faulting address.
//
// Note that this should only be called after verifying that the signalInfo has
// been generated by the kernel.
// Returns true if the signal info was patched, false otherwise.
func maybePatchSignalInfo(regs *arch.Registers, signalInfo *linux.SignalInfo) bool {
	if disableSyscallPatching ||
		signalInfo.Addr() < linux.VSyscallStartAddr ||
		signalInfo.Addr() >= linux.VSyscallEndAddr {
		return false
	}
	// The syscall event was triggered from vsyscall emulation.
	signalInfo.Signo = int32(linux.SIGSEGV)

	// Unwind the kernel emulation, if any has occurred. A SIGSYS is delivered
	// with the si_call_addr field pointing to the current RIP. This field
	// aligns with the si_addr field for a SIGSEGV, so we don't need to touch
	// anything there. We do need to unwind emulation however, so we set the
	// instruction pointer to the faulting value, and "unpop" the stack.
	regs.Rip = signalInfo.Addr()
	regs.Rsp -= 8
	return true
}

// enableCpuidFault enables cpuid-faulting.
//
// This may fail on older kernels or hardware, so we just disregard the result.
// Host CPUID will be enabled.
//
// This is safe to call in an afterFork context.
//
//go:nosplit
//go:norace
func enableCpuidFault() {
	hostsyscall.RawSyscall(unix.SYS_ARCH_PRCTL, linux.ARCH_SET_CPUID, 0, 0)
}

// appendArchSeccompRules append architecture specific seccomp rules when creating BPF program.
// Ref attachedThread() for more detail.
func appendArchSeccompRules(rules []seccomp.RuleSet) []seccomp.RuleSet {
	return append(rules, []seccomp.RuleSet{
		// Rules for trapping vsyscall access.
		{
			Rules: seccomp.MakeSyscallRules(map[uintptr]seccomp.SyscallRule{
				unix.SYS_GETTIMEOFDAY: seccomp.MatchAll{},
				unix.SYS_TIME:         seccomp.MatchAll{},
				unix.SYS_GETCPU:       seccomp.MatchAll{}, // SYS_GETCPU was not defined in package syscall on amd64.
			}),
			Action:   seccomp.Trap,
			Vsyscall: true,
		},
		{
			Rules: seccomp.MakeSyscallRules(map[uintptr]seccomp.SyscallRule{
				unix.SYS_ARCH_PRCTL: seccomp.Or{
					seccomp.PerArg{seccomp.EqualTo(linux.ARCH_SET_CPUID), seccomp.EqualTo(0)},
					seccomp.PerArg{seccomp.EqualTo(linux.ARCH_SET_FS)},
					seccomp.PerArg{seccomp.EqualTo(linux.ARCH_GET_FS)},
				},
			}),
			Action: seccomp.Allow,
		},
	}...)
}

func restoreArchSpecificState(ctx *sysmsg.ThreadContext, ac *arch.Context64) {
}

func setArchSpecificRegs(sysThread *sysmsgThread, regs *arch.Registers) {
	// Set gs_base; this is the only time we set it and we don't expect it to ever
	// change for any thread.
	regs.Gs_base = sysThread.msg.Self
}

func retrieveArchSpecificState(ctx *sysmsg.ThreadContext, ac *arch.Context64) {
}

func sigErrorToAccessType(sigError uint64) hostarch.AccessType {
	switch {
	case sigError&linux.X86_PF_WRITE != 0:
		return hostarch.Write
	case sigError&linux.X86_PF_INSTR != 0:
		return hostarch.Execute
	case sigError&linux.X86_PF_USER != 0:
		return hostarch.Read
	default:
		return hostarch.NoAccess
	}
}