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// Copyright 2019 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 arm64
// +build arm64
package ptrace
import (
"fmt"
"strings"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/seccomp"
"gvisor.dev/gvisor/pkg/sentry/arch"
)
const (
// maximumUserAddress is the largest possible user address.
maximumUserAddress = 0xfffffffff000
// stubInitAddress is the initial attempt link address for the stub.
// Only support 48bits VA currently.
stubInitAddress = 0xffffffff0000
// initRegsRipAdjustment is the size of the svc instruction.
initRegsRipAdjustment = 4
)
// resetSysemuRegs sets up emulation registers.
//
// This should be called prior to calling sysemu.
func (t *thread) resetSysemuRegs(regs *arch.Registers) {
}
// 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 (Pc, Sp, etc.).
regs := *initRegs
// Set our syscall number.
// r8 for the syscall number.
// r0-r6 is used to store the parameters.
regs.Regs[8] = uint64(sysno)
if len(args) >= 1 {
regs.Regs[0] = args[0].Uint64()
}
if len(args) >= 2 {
regs.Regs[1] = args[1].Uint64()
}
if len(args) >= 3 {
regs.Regs[2] = args[2].Uint64()
}
if len(args) >= 4 {
regs.Regs[3] = args[3].Uint64()
}
if len(args) >= 5 {
regs.Regs[4] = args[4].Uint64()
}
if len(args) >= 6 {
regs.Regs[5] = args[5].Uint64()
}
return regs
}
// isSingleStepping determines if the registers indicate single-stepping.
func isSingleStepping(regs *arch.Registers) bool {
// Refer to the ARM SDM D2.12.3: software step state machine
// return (regs.Pstate.SS == 1) && (MDSCR_EL1.SS == 1).
//
// Since the host Linux kernel will set MDSCR_EL1.SS on our behalf
// when we call a single-step ptrace command, we only need to check
// the Pstate.SS bit here.
return (regs.Pstate & arch.ARMTrapFlag) != 0
}
// updateSyscallRegs updates registers after finishing sysemu.
func updateSyscallRegs(regs *arch.Registers) {
// No special work is necessary.
return
}
// syscallReturnValue extracts a sensible return from registers.
func syscallReturnValue(regs *arch.Registers) (uintptr, error) {
rval := int64(regs.Regs[0])
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")
for i := 0; i < 31; i++ {
fmt.Fprintf(&m, "\tRegs[%d]\t = %016x\n", i, regs.Regs[i])
}
fmt.Fprintf(&m, "\tSp\t = %016x\n", regs.Sp)
fmt.Fprintf(&m, "\tPc\t = %016x\n", regs.Pc)
fmt.Fprintf(&m, "\tPstate\t = %016x\n", regs.Pstate)
return m.String()
}
// adjustInitregsRip adjust the current register RIP value to
// be just before the system call instruction excution
func (t *thread) adjustInitRegsRip() {
t.initRegs.Pc -= initRegsRipAdjustment
}
// Pass the expected PPID to the child via X7 when creating stub process
func initChildProcessPPID(initregs *arch.Registers, ppid int32) {
initregs.Regs[7] = uint64(ppid)
// R9 has to be set to 1 when creating stub process.
initregs.Regs[9] = 1
}
// 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.
func patchSignalInfo(regs *arch.Registers, signalInfo *linux.SignalInfo) {
if linux.Signal(signalInfo.Signo) == linux.SIGSYS {
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.Pc = signalInfo.Addr()
regs.Sp -= 8
}
}
// Noop on arm64.
//
//go:nosplit
func enableCpuidFault() {
}
// appendArchSeccompRules append architecture specific seccomp rules when creating BPF program.
// Ref attachedThread() for more detail.
func appendArchSeccompRules(rules []seccomp.RuleSet, defaultAction linux.BPFAction) []seccomp.RuleSet {
return rules
}
// probeSeccomp returns true if seccomp is run after ptrace notifications,
// which is generally the case for kernel version >= 4.8.
//
// On arm64, the support of PTRACE_SYSEMU was added in the 5.3 kernel, so
// probeSeccomp can always return true.
func probeSeccomp() bool {
return true
}
func (s *subprocess) arm64SyscallWorkaround(t *thread, regs *arch.Registers) {
// On ARM64, when ptrace stops on a system call, it uses the x7
// register to indicate whether the stop has been signalled from
// syscall entry or syscall exit. This means that we can't get a value
// of this register and we can't change it. More details are in the
// comment for tracehook_report_syscall in arch/arm64/kernel/ptrace.c.
//
// This happens only if we stop on a system call, so let's queue a
// signal, resume a stub thread and catch it on a signal handling.
t.NotifyInterrupt()
for {
if _, _, errno := unix.RawSyscall6(
unix.SYS_PTRACE,
unix.PTRACE_SYSEMU,
uintptr(t.tid), 0, 0, 0, 0); errno != 0 {
panic(fmt.Sprintf("ptrace sysemu failed: %v", errno))
}
// Wait for the syscall-enter stop.
sig := t.wait(stopped)
if sig == unix.SIGSTOP {
// SIGSTOP was delivered to another thread in the same thread
// group, which initiated another group stop. Just ignore it.
continue
}
if sig == (syscallEvent | unix.SIGTRAP) {
t.dumpAndPanic(fmt.Sprintf("unexpected syscall event"))
}
break
}
if err := t.getRegs(regs); err != nil {
panic(fmt.Sprintf("ptrace get regs failed: %v", err))
}
}
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