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subprocess.go
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subprocess.go
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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.
package systrap
import (
"fmt"
"os"
"runtime"
"sync"
"sync/atomic"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/pool"
"gvisor.dev/gvisor/pkg/seccomp"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/memmap"
"gvisor.dev/gvisor/pkg/sentry/pgalloc"
"gvisor.dev/gvisor/pkg/sentry/platform"
"gvisor.dev/gvisor/pkg/sentry/platform/systrap/sysmsg"
"gvisor.dev/gvisor/pkg/sentry/platform/systrap/usertrap"
"gvisor.dev/gvisor/pkg/sentry/usage"
)
var (
// globalPool tracks all subprocesses in various state: active or available for
// reuse.
globalPool = subprocessPool{}
// maximumUserAddress is the largest possible user address.
maximumUserAddress = linux.TaskSize
// stubInitAddress is the initial attempt link address for the stub.
stubInitAddress = linux.TaskSize
// maxRandomOffsetOfStubAddress is the maximum offset for randomizing a
// stub address. It is set to the default value of mm.mmap_rnd_bits.
//
// Note: Tools like ThreadSanitizer don't like when the memory layout
// is changed significantly.
maxRandomOffsetOfStubAddress = (linux.TaskSize >> 7) & ^(uintptr(hostarch.PageSize) - 1)
// maxStubUserAddress is the largest possible user address for
// processes running inside gVisor. It is fixed because
// * we don't want to reveal a stub address.
// * it has to be the same across checkpoint/restore.
maxStubUserAddress = maximumUserAddress - maxRandomOffsetOfStubAddress
)
// Linux kernel errnos which "should never be seen by user programs", but will
// be revealed to ptrace syscall exit tracing.
//
// These constants are only used in subprocess.go.
const (
ERESTARTSYS = unix.Errno(512)
ERESTARTNOINTR = unix.Errno(513)
ERESTARTNOHAND = unix.Errno(514)
)
// thread is a traced thread; it is a thread identifier.
//
// This is a convenience type for defining ptrace operations.
type thread struct {
tgid int32
tid int32
// sysmsgStackID is a stack ID in subprocess.sysmsgStackPool.
sysmsgStackID uint64
// initRegs are the initial registers for the first thread.
//
// These are used for the register set for system calls.
initRegs arch.Registers
}
// requestThread is used to request a new sysmsg thread. A thread identifier will
// be sent into the thread channel.
type requestThread struct {
thread chan *thread
}
// requestStub is used to request a new stub process.
type requestStub struct {
done chan *thread
}
// maxSysmsgThreads specifies the maximum number of system threads that a
// subprocess can create in context decoupled mode.
// TODO(b/268366549): Replace maxSystemThreads below.
var maxSysmsgThreads = runtime.GOMAXPROCS(0)
const (
// maxSystemThreads specifies the maximum number of system threads that a
// subprocess may create in order to process the contexts.
maxSystemThreads = 4096
// maxGuestContexts specifies the maximum number of task contexts that a
// subprocess can handle.
maxGuestContexts = 4096
// invalidContextID specifies an invalid ID.
invalidContextID = maxGuestContexts + 1
// invalidThreadID is used to indicate that a context is not being worked on by
// any sysmsg thread.
invalidThreadID uint32 = uint32(maxGuestContexts) + 1
)
// subprocess is a collection of threads being traced.
type subprocess struct {
platform.NoAddressSpaceIO
subprocessRefs
// requests is used to signal creation of new threads.
requests chan any
// sysmsgInitRegs is used to reset sysemu regs.
sysmsgInitRegs arch.Registers
// mu protects the following fields.
mu sync.Mutex
// faultedContexts is the set of contexts for which it's possible that
// context.lastFaultSP == this subprocess.
faultedContexts map[*context]struct{}
// sysmsgStackPool is a pool of available sysmsg stacks.
sysmsgStackPool pool.Pool
// threadContextPool is a pool of available sysmsg.ThreadContext IDs.
threadContextPool pool.Pool
// threadContextRegion defines the ThreadContext memory region start
// within the sentry address space.
threadContextRegion uintptr
// memoryFile is used to allocate a sysmsg stack which is shared
// between a stub process and the Sentry.
memoryFile *pgalloc.MemoryFile
// usertrap is the state of the usertrap table which contains syscall
// trampolines.
usertrap *usertrap.State
syscallThreadMu sync.Mutex
syscallThread *syscallThread
// sysmsgThreadsMu protects sysmsgThreads and numSysmsgThreads
sysmsgThreadsMu sync.Mutex
// sysmsgThreads is a collection of all active sysmsg threads in the
// subprocess.
sysmsgThreads map[uint32]*sysmsgThread
// numSysmsgThreads counts the number of active sysmsg threads; we use a
// counter instead of using len(sysmsgThreads) because we need to synchronize
// how many threads get created _before_ the creation happens.
numSysmsgThreads int
// contextQueue is a queue of all contexts that are ready to switch back to
// user mode.
contextQueue *contextQueue
}
func (s *subprocess) initSyscallThread(ptraceThread *thread) error {
s.syscallThreadMu.Lock()
defer s.syscallThreadMu.Unlock()
id, ok := s.sysmsgStackPool.Get()
if !ok {
panic("unable to allocate a sysmsg stub thread")
}
ptraceThread.sysmsgStackID = id
t := syscallThread{
subproc: s,
thread: ptraceThread,
}
if err := t.init(); err != nil {
panic(fmt.Sprintf("failed to create a syscall thread"))
}
s.syscallThread = &t
s.syscallThread.detach()
return nil
}
// handlePtraceSyscallRequest executes system calls that can't be run via
// syscallThread without using ptrace. Look at the description of syscallThread
// to get more details about its limitations.
func (s *subprocess) handlePtraceSyscallRequest(req any) {
s.syscallThreadMu.Lock()
defer s.syscallThreadMu.Unlock()
runtime.LockOSThread()
defer runtime.UnlockOSThread()
s.syscallThread.attach()
defer s.syscallThread.detach()
ptraceThread := s.syscallThread.thread
switch req.(type) {
case requestThread:
r := req.(requestThread)
t, err := ptraceThread.clone()
if err != nil {
// Should not happen: not recoverable.
panic(fmt.Sprintf("error initializing first thread: %v", err))
}
// Since the new thread was created with
// clone(CLONE_PTRACE), it will begin execution with
// SIGSTOP pending and with this thread as its tracer.
// (Hopefully nobody tgkilled it with a signal <
// SIGSTOP before the SIGSTOP was delivered, in which
// case that signal would be delivered before SIGSTOP.)
if sig := t.wait(stopped); sig != unix.SIGSTOP {
panic(fmt.Sprintf("error waiting for new clone: expected SIGSTOP, got %v", sig))
}
id, ok := s.sysmsgStackPool.Get()
if !ok {
panic("unable to allocate a sysmsg stub thread")
}
t.sysmsgStackID = id
if _, _, e := unix.RawSyscall(unix.SYS_TGKILL, uintptr(t.tgid), uintptr(t.tid), uintptr(unix.SIGSTOP)); e != 0 {
panic(fmt.Sprintf("tkill failed: %v", e))
}
// Detach the thread.
t.detach()
t.initRegs = ptraceThread.initRegs
// Return the thread.
r.thread <- t
case requestStub:
r := req.(requestStub)
t, err := ptraceThread.createStub()
if err != nil {
panic(fmt.Sprintf("unable to create a stub process: %s", err))
}
r.done <- t
}
}
// newSubprocess returns a usable subprocess.
//
// This will either be a newly created subprocess, or one from the global pool.
// The create function will be called in the latter case, which is guaranteed
// to happen with the runtime thread locked.
func newSubprocess(create func() (*thread, error), memoryFile *pgalloc.MemoryFile) (*subprocess, error) {
if sp := globalPool.fetchAvailable(); sp != nil {
sp.subprocessRefs.InitRefs()
sp.usertrap = usertrap.New()
return sp, nil
}
// The following goroutine is responsible for creating the first traced
// thread, and responding to requests to make additional threads in the
// traced process. The process will be killed and reaped when the
// request channel is closed, which happens in Release below.
requests := make(chan any)
// Ready.
sp := &subprocess{
requests: requests,
faultedContexts: make(map[*context]struct{}),
sysmsgStackPool: pool.Pool{Start: 0, Limit: maxSystemThreads},
threadContextPool: pool.Pool{Start: 0, Limit: maxGuestContexts},
memoryFile: memoryFile,
sysmsgThreads: make(map[uint32]*sysmsgThread),
}
sp.subprocessRefs.InitRefs()
runtime.LockOSThread()
defer runtime.UnlockOSThread()
// Initialize the syscall thread.
ptraceThread, err := create()
if err != nil {
return nil, err
}
sp.sysmsgInitRegs = ptraceThread.initRegs
if err := sp.initSyscallThread(ptraceThread); err != nil {
return nil, err
}
go func() { // S/R-SAFE: Platform-related.
// Wait for requests to create threads.
for req := range requests {
sp.handlePtraceSyscallRequest(req)
}
// Requests should never be closed.
panic("unreachable")
}()
sp.unmap()
sp.usertrap = usertrap.New()
sp.mapSharedRegions()
sp.mapPrivateRegions()
// Create the initial sysmsg thread.
if contextDecouplingExp {
atomic.AddUint32(&sp.contextQueue.numActiveThreads, 1)
if _, err := sp.createSysmsgThread(nil, nil, nil); err != nil {
atomic.AddUint32(&sp.contextQueue.numActiveThreads, ^uint32(0))
return nil, err
}
sp.numSysmsgThreads++
}
return sp, nil
}
// mapSharedRegions maps the shared regions that are used between the subprocess
// and ALL of the subsequently created sysmsg threads into both the sentry and
// the syscall thread.
//
// Should be called before any sysmsg threads are created.
// Initializes s.contextQueue and s.threadContextRegion.
func (s *subprocess) mapSharedRegions() {
if s.contextQueue != nil || s.threadContextRegion != 0 {
panic("contextQueue or threadContextRegion was already initialized")
}
opts := pgalloc.AllocOpts{
Kind: usage.System,
Dir: pgalloc.TopDown,
}
if contextDecouplingExp {
// Map shared regions into the sentry.
contextQueueFR, contextQueue := mmapContextQueueForSentry(s.memoryFile, opts)
contextQueue.init()
// Map thread context region into the syscall thread.
_, err := s.syscallThread.syscall(
unix.SYS_MMAP,
arch.SyscallArgument{Value: uintptr(stubContextQueueRegion)},
arch.SyscallArgument{Value: uintptr(contextQueueFR.Length())},
arch.SyscallArgument{Value: uintptr(unix.PROT_READ | unix.PROT_WRITE)},
arch.SyscallArgument{Value: uintptr(unix.MAP_SHARED | unix.MAP_FILE | unix.MAP_FIXED)},
arch.SyscallArgument{Value: uintptr(s.memoryFile.FD())},
arch.SyscallArgument{Value: uintptr(contextQueueFR.Start)})
if err != nil {
panic(fmt.Sprintf("failed to mmap context queue region into syscall thread: %v", err))
}
s.contextQueue = contextQueue
}
// Map thread context region into the sentry.
threadContextFR, err := s.memoryFile.Allocate(uint64(stubContextRegionLen), opts)
if err != nil {
panic(fmt.Sprintf("failed to allocate a new subprocess context memory region"))
}
sentryThreadContextRegionAddr, _, errno := unix.RawSyscall6(
unix.SYS_MMAP,
0,
uintptr(threadContextFR.Length()),
unix.PROT_WRITE|unix.PROT_READ,
unix.MAP_SHARED|unix.MAP_FILE,
uintptr(s.memoryFile.FD()), uintptr(threadContextFR.Start))
if errno != 0 {
panic(fmt.Sprintf("mmap failed for subprocess context memory region: %v", errno))
}
// Map thread context region into the syscall thread.
if _, err := s.syscallThread.syscall(
unix.SYS_MMAP,
arch.SyscallArgument{Value: uintptr(stubContextRegion)},
arch.SyscallArgument{Value: uintptr(threadContextFR.Length())},
arch.SyscallArgument{Value: uintptr(unix.PROT_READ | unix.PROT_WRITE)},
arch.SyscallArgument{Value: uintptr(unix.MAP_SHARED | unix.MAP_FILE | unix.MAP_FIXED)},
arch.SyscallArgument{Value: uintptr(s.memoryFile.FD())},
arch.SyscallArgument{Value: uintptr(threadContextFR.Start)}); err != nil {
panic(fmt.Sprintf("failed to mmap context queue region into syscall thread: %v", err))
}
s.threadContextRegion = sentryThreadContextRegionAddr
}
func (s *subprocess) mapPrivateRegions() {
if contextDecouplingExp {
_, err := s.syscallThread.syscall(
unix.SYS_MMAP,
arch.SyscallArgument{Value: uintptr(stubSpinningThreadQueueAddr)},
arch.SyscallArgument{Value: uintptr(sysmsg.SpinningQueueMemSize)},
arch.SyscallArgument{Value: uintptr(unix.PROT_READ | unix.PROT_WRITE)},
arch.SyscallArgument{Value: uintptr(unix.MAP_PRIVATE | unix.MAP_ANONYMOUS | unix.MAP_FIXED)},
arch.SyscallArgument{Value: 0},
arch.SyscallArgument{Value: 0})
if err != nil {
panic(fmt.Sprintf("failed to mmap spinning queue region into syscall thread: %v", err))
}
}
}
// unmap unmaps non-stub regions of the process.
//
// This will panic on failure (which should never happen).
func (s *subprocess) unmap() {
s.Unmap(0, uint64(stubStart))
if maximumUserAddress != stubEnd {
s.Unmap(hostarch.Addr(stubEnd), uint64(maximumUserAddress-stubEnd))
}
}
// Release kills the subprocess.
//
// Just kidding! We can't safely co-ordinate the detaching of all the
// tracees (since the tracers are random runtime threads, and the process
// won't exit until tracers have been notifier).
//
// Therefore we simply unmap everything in the subprocess and return it to the
// globalPool. This has the added benefit of reducing creation time for new
// subprocesses.
func (s *subprocess) Release() {
s.unmap()
s.DecRef(s.release)
}
// release returns the subprocess to the global pool.
func (s *subprocess) release() {
globalPool.markAvailable(s)
}
// newThread creates a new traced thread.
//
// Precondition: the OS thread must be locked.
func (s *subprocess) newThread() *thread {
// Ask the first thread to create a new one.
var r requestThread
r.thread = make(chan *thread)
s.requests <- r
t := <-r.thread
// Attach the subprocess to this one.
t.attach()
// Return the new thread, which is now bound.
return t
}
// attach attaches to the thread.
func (t *thread) attach() {
if _, _, errno := unix.RawSyscall6(unix.SYS_PTRACE, unix.PTRACE_ATTACH, uintptr(t.tid), 0, 0, 0, 0); errno != 0 {
panic(fmt.Sprintf("unable to attach: %v", errno))
}
// PTRACE_ATTACH sends SIGSTOP, and wakes the tracee if it was already
// stopped from the SIGSTOP queued by CLONE_PTRACE (see inner loop of
// newSubprocess), so we always expect to see signal-delivery-stop with
// SIGSTOP.
if sig := t.wait(stopped); sig != unix.SIGSTOP {
panic(fmt.Sprintf("wait failed: expected SIGSTOP, got %v", sig))
}
// Initialize options.
t.init()
}
func (t *thread) grabInitRegs() {
// Grab registers.
//
// Note that we adjust the current register RIP value to be just before
// the current system call executed. This depends on the definition of
// the stub itself.
if err := t.getRegs(&t.initRegs); err != nil {
panic(fmt.Sprintf("ptrace get regs failed: %v", err))
}
t.adjustInitRegsRip()
t.initRegs.SetStackPointer(0)
}
// detach detaches from the thread.
//
// Because the SIGSTOP is not suppressed, the thread will enter group-stop.
func (t *thread) detach() {
if _, _, errno := unix.RawSyscall6(unix.SYS_PTRACE, unix.PTRACE_DETACH, uintptr(t.tid), 0, uintptr(unix.SIGSTOP), 0, 0); errno != 0 {
panic(fmt.Sprintf("can't detach new clone: %v", errno))
}
}
// waitOutcome is used for wait below.
type waitOutcome int
const (
// stopped indicates that the process was stopped.
stopped waitOutcome = iota
// killed indicates that the process was killed.
killed
)
func (t *thread) Debugf(format string, v ...any) {
prefix := fmt.Sprintf("%8d:", t.tid)
log.DebugfAtDepth(1, prefix+format, v...)
}
func (t *thread) dumpAndPanic(message string) {
var regs arch.Registers
message += "\n"
if err := t.getRegs(®s); err == nil {
message += dumpRegs(®s)
} else {
log.Warningf("unable to get registers: %v", err)
}
message += fmt.Sprintf("stubStart\t = %016x\n", stubStart)
panic(message)
}
func (t *thread) dumpRegs(message string) {
var regs arch.Registers
message += "\n"
if err := t.getRegs(®s); err == nil {
message += dumpRegs(®s)
} else {
log.Warningf("unable to get registers: %v", err)
}
log.Infof("%s", message)
}
func (t *thread) unexpectedStubExit() {
msg, err := t.getEventMessage()
status := unix.WaitStatus(msg)
if status.Signaled() && status.Signal() == unix.SIGKILL {
// SIGKILL can be only sent by a user or OOM-killer. In both
// these cases, we don't need to panic. There is no reasons to
// think that something wrong in gVisor.
log.Warningf("The ptrace stub process %v has been killed by SIGKILL.", t.tgid)
pid := os.Getpid()
unix.Tgkill(pid, pid, unix.Signal(unix.SIGKILL))
}
t.dumpAndPanic(fmt.Sprintf("wait failed: the process %d:%d exited: %x (err %v)", t.tgid, t.tid, msg, err))
}
// wait waits for a stop event.
//
// Precondition: outcome is a valid waitOutcome.
func (t *thread) wait(outcome waitOutcome) unix.Signal {
var status unix.WaitStatus
for {
r, err := unix.Wait4(int(t.tid), &status, unix.WALL|unix.WUNTRACED, nil)
if err == unix.EINTR || err == unix.EAGAIN {
// Wait was interrupted; wait again.
continue
} else if err != nil {
panic(fmt.Sprintf("ptrace wait failed: %v", err))
}
if int(r) != int(t.tid) {
panic(fmt.Sprintf("ptrace wait returned %v, expected %v", r, t.tid))
}
switch outcome {
case stopped:
if !status.Stopped() {
t.dumpAndPanic(fmt.Sprintf("ptrace status unexpected: got %v, wanted stopped", status))
}
stopSig := status.StopSignal()
if stopSig == 0 {
continue // Spurious stop.
}
if stopSig == unix.SIGTRAP {
if status.TrapCause() == unix.PTRACE_EVENT_EXIT {
t.unexpectedStubExit()
}
// Re-encode the trap cause the way it's expected.
return stopSig | unix.Signal(status.TrapCause()<<8)
}
// Not a trap signal.
return stopSig
case killed:
if !status.Exited() && !status.Signaled() {
t.dumpAndPanic(fmt.Sprintf("ptrace status unexpected: got %v, wanted exited", status))
}
return unix.Signal(status.ExitStatus())
default:
// Should not happen.
t.dumpAndPanic(fmt.Sprintf("unknown outcome: %v", outcome))
}
}
}
// destroy kills the thread.
//
// Note that this should not be used in the general case; the death of threads
// will typically cause the death of the parent. This is a utility method for
// manually created threads.
func (t *thread) destroy() {
t.detach()
unix.Tgkill(int(t.tgid), int(t.tid), unix.Signal(unix.SIGKILL))
t.wait(killed)
}
// init initializes trace options.
func (t *thread) init() {
// Set the TRACESYSGOOD option to differentiate real SIGTRAP.
// set PTRACE_O_EXITKILL to ensure that the unexpected exit of the
// sentry will immediately kill the associated stubs.
_, _, errno := unix.RawSyscall6(
unix.SYS_PTRACE,
unix.PTRACE_SETOPTIONS,
uintptr(t.tid),
0,
unix.PTRACE_O_TRACESYSGOOD|unix.PTRACE_O_TRACEEXIT|unix.PTRACE_O_EXITKILL,
0, 0)
if errno != 0 {
panic(fmt.Sprintf("ptrace set options failed: %v", errno))
}
}
// syscall executes a system call cycle in the traced context.
//
// This is _not_ for use by application system calls, rather it is for use when
// a system call must be injected into the remote context (e.g. mmap, munmap).
// Note that clones are handled separately.
func (t *thread) syscall(regs *arch.Registers) (uintptr, error) {
// Set registers.
if err := t.setRegs(regs); err != nil {
panic(fmt.Sprintf("ptrace set regs failed: %v", err))
}
for {
// Execute the syscall instruction. The task has to stop on the
// trap instruction which is right after the syscall
// instruction.
if _, _, errno := unix.RawSyscall6(unix.SYS_PTRACE, unix.PTRACE_CONT, uintptr(t.tid), 0, 0, 0, 0); errno != 0 {
panic(fmt.Sprintf("ptrace syscall-enter failed: %v", errno))
}
sig := t.wait(stopped)
if sig == unix.SIGTRAP {
// Reached syscall-enter-stop.
break
} else {
// Some other signal caused a thread stop; ignore.
if sig != unix.SIGSTOP && sig != unix.SIGCHLD {
log.Warningf("The thread %d:%d has been interrupted by %d", t.tgid, t.tid, sig)
}
continue
}
}
// Grab registers.
if err := t.getRegs(regs); err != nil {
panic(fmt.Sprintf("ptrace get regs failed: %v", err))
}
return syscallReturnValue(regs)
}
// syscallIgnoreInterrupt ignores interrupts on the system call thread and
// restarts the syscall if the kernel indicates that should happen.
func (t *thread) syscallIgnoreInterrupt(
initRegs *arch.Registers,
sysno uintptr,
args ...arch.SyscallArgument) (uintptr, error) {
for {
regs := createSyscallRegs(initRegs, sysno, args...)
rval, err := t.syscall(®s)
switch err {
case ERESTARTSYS:
continue
case ERESTARTNOINTR:
continue
case ERESTARTNOHAND:
continue
default:
return rval, err
}
}
}
// NotifyInterrupt implements interrupt.Receiver.NotifyInterrupt.
func (t *thread) NotifyInterrupt() {
unix.Tgkill(int(t.tgid), int(t.tid), unix.Signal(platform.SignalInterrupt))
}
// switchToApp is called from the main SwitchToApp entrypoint.
//
// This function returns true on a system call, false on a signal.
// The second return value is true if a syscall instruction can be replaced on
// a function call.
func (s *subprocess) switchToApp(c *context, ac *arch.Context64) (isSyscall bool, shouldPatchSyscall bool, err error) {
// Get sysmsg thread bound to the context; no-op if contextDecoupling is on.
regs := &ac.StateData().Regs
sysThread, err := s.getSysmsgThread(regs, c, ac)
if err != nil {
return false, false, err
}
// Reset necessary registers.
s.resetSysemuRegs(regs)
ctx := c.sharedContext
ctx.shared.Regs = regs.PtraceRegs
restoreArchSpecificState(ctx.shared, ac)
// Check for interrupts, and ensure that future interrupts signal the context.
if !c.interrupt.Enable(c.sharedContext) {
// Pending interrupt; simulate.
ctx.clearInterrupt()
c.signalInfo = linux.SignalInfo{Signo: int32(platform.SignalInterrupt)}
return false, false, nil
}
defer func() {
ctx.clearInterrupt()
c.interrupt.Disable()
}()
if contextDecouplingExp {
restoreFPState(nil, ctx, 0, c, ac)
// Place the context onto the context queue.
ctx.setState(sysmsg.ContextStateNone)
s.contextQueue.add(uint32(ctx.contextID))
s.waitOnState(ctx)
// Check if there's been an error.
threadID := ctx.threadID()
if threadID != invalidThreadID {
if sysThread, ok := s.sysmsgThreads[threadID]; ok && sysThread.msg.Err != 0 {
msg := sysThread.msg
panic(fmt.Sprintf("stub thread %d failed: err 0x%x line %d: %s", sysThread.thread.tid, msg.Err, msg.Line, msg))
}
log.Warningf("systrap: found unexpected ThreadContext.ThreadID field, expected %d found %d", invalidThreadID, threadID)
}
} else {
msg := sysThread.msg
t := sysThread.thread
restoreFPState(msg, ctx, sysThread.fpuStateToMsgOffset, c, ac)
msg.EnableSentryFastPath()
sysThread.waitEvent(sysmsg.ThreadStateDone, ctx)
// Check if there's been an error.
if msg.Err != 0 {
panic(fmt.Sprintf("stub thread %d failed: err %d line %d: %s", t.tid, msg.Err, msg.Line, msg))
}
if ctx.state() != sysmsg.ContextStateSyscallTrap {
var err error
sysThread.fpuStateToMsgOffset, err = msg.FPUStateOffset()
if err != nil {
return false, false, err
}
}
}
// Copy register state locally.
regs.PtraceRegs = ctx.shared.Regs
retrieveArchSpecificState(ctx.shared, ac)
c.needToPullFullState = true
// We have a signal. We verify however, that the signal was
// either delivered from the kernel or from this process. We
// don't respect other signals.
c.signalInfo = ctx.shared.SignalInfo
ctxState := ctx.state()
if ctxState == sysmsg.ContextStateSyscallCanBePatched {
ctxState = sysmsg.ContextStateSyscall
shouldPatchSyscall = true
}
if ctxState == sysmsg.ContextStateSyscall || ctxState == sysmsg.ContextStateSyscallTrap {
if maybePatchSignalInfo(regs, &c.signalInfo) {
return false, false, nil
}
updateSyscallRegs(regs)
return true, shouldPatchSyscall, nil
} else if ctxState != sysmsg.ContextStateFault {
panic(fmt.Sprintf("unknown context state: %v", ctxState))
}
return false, false, nil
}
func (s *subprocess) waitOnState(ctx *sharedContext) {
kicked := false
slowPath := false
start := cputicks()
handshake := false
if atomic.LoadUint32(&s.contextQueue.numActiveThreads) == 0 {
kicked = s.kickSysmsgThread()
}
for curState := ctx.state(); curState == sysmsg.ContextStateNone; curState = ctx.state() {
if !slowPath {
delta := uint64(cputicks() - start)
if delta > deepSleepTimeout {
ctx.disableSentryFastPath()
slowPath = true
continue
}
if !handshake {
if ctx.isAcked() {
handshake = true
continue
}
if !kicked && delta > handshakeTimeout {
kicked = s.kickSysmsgThread()
}
}
spinloop()
} else {
// If the context already received a handshake then it knows it's being
// worked on.
if !kicked && !handshake {
kicked = s.kickSysmsgThread()
}
ctx.sleepOnState(curState)
}
}
ctx.resetAcked()
ctx.enableSentryFastPath()
}
func (s *subprocess) kickSysmsgThread() bool {
// numActiveContexts and numActiveThreads can be changed from stub
// threads that work with the contextQueue without any locks. The idea
// here is that any stub thread that gets CPU time can make some
// progress. In stub threads, we can use only spinlock-like
// synchronizations, but they don't work well because a thread that
// holds a lock can be preempted by another threads that is waiting for
// the same lock.
nrActiveContexts := atomic.LoadUint32(&s.contextQueue.numActiveContexts)
nrActiveThreads := atomic.LoadUint32(&s.contextQueue.numActiveThreads)
if nrActiveContexts != 0 && nrActiveThreads >= nrActiveContexts {
// This can happen when one or more stub threads are
// waiting for cpu time. The host probably has more
// running tasks than a number of cpu-s.
return false
}
s.sysmsgThreadsMu.Lock()
nrActiveContexts = atomic.LoadUint32(&s.contextQueue.numActiveContexts)
nrActiveThreads = atomic.LoadUint32(&s.contextQueue.numActiveThreads)
if nrActiveContexts != 0 && nrActiveThreads >= nrActiveContexts {
s.sysmsgThreadsMu.Unlock()
return false
}
if s.numSysmsgThreads > int(nrActiveThreads) {
for _, t := range s.sysmsgThreads {
if kicked, _ := t.msg.WakeSysmsgThread(); kicked {
s.sysmsgThreadsMu.Unlock()
return true
}
}
s.sysmsgThreadsMu.Unlock()
// Threads are kicked only here under sysmsgThreadsMu. It means
// that this case is possible only if one thread decides to
// fall asleep but then change its mind. Look at
// sysmsg_lib.c:get_context for more details.
return false
}
if s.numSysmsgThreads < maxSysmsgThreads {
s.numSysmsgThreads++
s.sysmsgThreadsMu.Unlock()
atomic.AddUint32(&s.contextQueue.numActiveThreads, 1)
if _, err := s.createSysmsgThread(nil, nil, nil); err != nil {
log.Warningf("Unable to create a new stub thread: %s", err)
atomic.AddUint32(&s.contextQueue.numActiveThreads, ^uint32(0))
s.sysmsgThreadsMu.Lock()
s.numSysmsgThreads--
s.sysmsgThreadsMu.Unlock()
return false
}
return true
}
s.sysmsgThreadsMu.Unlock()
return false
}
// syscall executes the given system call without handling interruptions.
func (s *subprocess) syscall(sysno uintptr, args ...arch.SyscallArgument) (uintptr, error) {
s.syscallThreadMu.Lock()
defer s.syscallThreadMu.Unlock()
return s.syscallThread.syscall(sysno, args...)
}
// MapFile implements platform.AddressSpace.MapFile.
func (s *subprocess) MapFile(addr hostarch.Addr, f memmap.File, fr memmap.FileRange, at hostarch.AccessType, precommit bool) error {
var flags int
if precommit {
flags |= unix.MAP_POPULATE
}
_, err := s.syscall(
unix.SYS_MMAP,
arch.SyscallArgument{Value: uintptr(addr)},
arch.SyscallArgument{Value: uintptr(fr.Length())},
arch.SyscallArgument{Value: uintptr(at.Prot())},
arch.SyscallArgument{Value: uintptr(flags | unix.MAP_SHARED | unix.MAP_FIXED)},
arch.SyscallArgument{Value: uintptr(f.FD())},
arch.SyscallArgument{Value: uintptr(fr.Start)})
return err
}
// Unmap implements platform.AddressSpace.Unmap.
func (s *subprocess) Unmap(addr hostarch.Addr, length uint64) {
ar, ok := addr.ToRange(length)
if !ok {
panic(fmt.Sprintf("addr %#x + length %#x overflows", addr, length))
}
s.mu.Lock()
for c := range s.faultedContexts {
c.mu.Lock()
if c.lastFaultSP == s && ar.Contains(c.lastFaultAddr) {
// Forget the last fault so that if c faults again, the fault isn't
// incorrectly reported as a write fault. If this is being called
// due to munmap() of the corresponding vma, handling of the second
// fault will fail anyway.
c.lastFaultSP = nil
delete(s.faultedContexts, c)
}
c.mu.Unlock()
}
s.mu.Unlock()
_, err := s.syscall(
unix.SYS_MUNMAP,
arch.SyscallArgument{Value: uintptr(addr)},
arch.SyscallArgument{Value: uintptr(length)})
if err != nil {
// We never expect this to happen.
panic(fmt.Sprintf("munmap(%x, %x)) failed: %v", addr, length, err))
}
}
func (s *subprocess) PullFullState(c *context, ac *arch.Context64) error {
if !c.sharedContext.isActiveInSubprocess(s) {
panic("Attempted to PullFullState for context that is not used in subprocess")
}
if contextDecouplingExp {
saveFPState(nil, c.sharedContext, 0, c, ac)
} else {
sysThread, err := s.getSysmsgThread(&ac.StateData().Regs, c, ac)
if err != nil {
return err
}
saveFPState(sysThread.msg, c.sharedContext, sysThread.fpuStateToMsgOffset, c, ac)
}
return nil
}
// getSysmsgThread returns a sysmsg thread for the specified context.
// (Unused if contextDecouplingExp=true).
func (s *subprocess) getSysmsgThread(tregs *arch.Registers, c *context, ac *arch.Context64) (*sysmsgThread, error) {
if contextDecouplingExp {
return nil, nil
}
sysThread := c.sysmsgThread
if sysThread != nil && sysThread.subproc != s {
// This can happen if a new address space
// has been created (e.g. fork).
sysThread.destroy()
sysThread = nil
}
if sysThread != nil {
return sysThread, nil
}
return s.createSysmsgThread(tregs, c, ac)
}
// createSysmsgThread creates a new sysmsg thread.
// If contextDecouplingExp=false, the thread starts working on the given context.
// Otherwise the given function parameters are not used, and the thread starts
// processing any available context in the context queue.
func (s *subprocess) createSysmsgThread(tregs *arch.Registers, c *context, ac *arch.Context64) (*sysmsgThread, error) {
if contextDecouplingExp {
// We will not bind any specific context to this thread. We will still use
// tregs to setup the thread though.
tregs = &arch.Registers{}
}
// Create a new seccomp process.
var r requestThread
r.thread = make(chan *thread)
s.requests <- r
p := <-r.thread
runtime.LockOSThread()
defer runtime.UnlockOSThread()