1 files changed, 549 insertions, 0 deletions
diff --git a/pkg/sentry/syscalls/linux/sys_poll.go b/pkg/sentry/syscalls/linux/sys_poll.go
new file mode 100644
index 000000000..e32099dd4
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/sys_poll.go
@@ -0,0 +1,549 @@
+// 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 linux
+
+import (
+	"time"
+
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/kdefs"
+	ktime "gvisor.googlesource.com/gvisor/pkg/sentry/kernel/time"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/limits"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+	"gvisor.googlesource.com/gvisor/pkg/waiter"
+)
+
+// fileCap is the maximum allowable files for poll & select.
+const fileCap = 1024 * 1024
+
+// Masks for "readable", "writable", and "exceptional" events as defined by
+// select(2).
+const (
+	// selectReadEvents is analogous to the Linux kernel's
+	// fs/select.c:POLLIN_SET.
+	selectReadEvents = linux.POLLIN | linux.POLLHUP | linux.POLLERR
+
+	// selectWriteEvents is analogous to the Linux kernel's
+	// fs/select.c:POLLOUT_SET.
+	selectWriteEvents = linux.POLLOUT | linux.POLLERR
+
+	// selectExceptEvents is analogous to the Linux kernel's
+	// fs/select.c:POLLEX_SET.
+	selectExceptEvents = linux.POLLPRI
+)
+
+// pollState tracks the associated file descriptor and waiter of a PollFD.
+type pollState struct {
+	file   *fs.File
+	waiter waiter.Entry
+}
+
+// initReadiness gets the current ready mask for the file represented by the FD
+// stored in pfd.FD. If a channel is passed in, the waiter entry in "state" is
+// used to register with the file for event notifications, and a reference to
+// the file is stored in "state".
+func initReadiness(t *kernel.Task, pfd *linux.PollFD, state *pollState, ch chan struct{}) {
+	if pfd.FD < 0 {
+		pfd.REvents = 0
+		return
+	}
+
+	file := t.FDMap().GetFile(kdefs.FD(pfd.FD))
+	if file == nil {
+		pfd.REvents = linux.POLLNVAL
+		return
+	}
+
+	if ch == nil {
+		defer file.DecRef()
+	} else {
+		state.file = file
+		state.waiter, _ = waiter.NewChannelEntry(ch)
+		file.EventRegister(&state.waiter, waiter.EventMaskFromLinux(uint32(pfd.Events)))
+	}
+
+	r := file.Readiness(waiter.EventMaskFromLinux(uint32(pfd.Events)))
+	pfd.REvents = int16(r.ToLinux()) & pfd.Events
+}
+
+// releaseState releases all the pollState in "state".
+func releaseState(state []pollState) {
+	for i := range state {
+		if state[i].file != nil {
+			state[i].file.EventUnregister(&state[i].waiter)
+			state[i].file.DecRef()
+		}
+	}
+}
+
+// pollBlock polls the PollFDs in "pfd" with a bounded time specified in "timeout"
+// when "timeout" is greater than zero.
+//
+// pollBlock returns the remaining timeout, which is always 0 on a timeout; and 0 or
+// positive if interrupted by a signal.
+func pollBlock(t *kernel.Task, pfd []linux.PollFD, timeout time.Duration) (time.Duration, uintptr, error) {
+	var ch chan struct{}
+	if timeout != 0 {
+		ch = make(chan struct{}, 1)
+	}
+
+	// Register for event notification in the files involved if we may
+	// block (timeout not zero). Once we find a file that has a non-zero
+	// result, we stop registering for events but still go through all files
+	// to get their ready masks.
+	state := make([]pollState, len(pfd))
+	defer releaseState(state)
+	n := uintptr(0)
+	for i := range pfd {
+		initReadiness(t, &pfd[i], &state[i], ch)
+		if pfd[i].REvents != 0 {
+			n++
+			ch = nil
+		}
+	}
+
+	if timeout == 0 {
+		return timeout, n, nil
+	}
+
+	forever := timeout < 0
+
+	for n == 0 {
+		var err error
+		// Wait for a notification.
+		timeout, err = t.BlockWithTimeout(ch, !forever, timeout)
+		if err != nil {
+			if err == syserror.ETIMEDOUT {
+				err = nil
+			}
+			return timeout, 0, err
+		}
+
+		// We got notified, count how many files are ready. If none,
+		// then this was a spurious notification, and we just go back
+		// to sleep with the remaining timeout.
+		for i := range state {
+			if state[i].file == nil {
+				continue
+			}
+
+			r := state[i].file.Readiness(waiter.EventMaskFromLinux(uint32(pfd[i].Events)))
+			rl := int16(r.ToLinux()) & pfd[i].Events
+			if rl != 0 {
+				pfd[i].REvents = rl
+				n++
+			}
+		}
+	}
+
+	return timeout, n, nil
+}
+
+// CopyInPollFDs copies an array of struct pollfd unless nfds exceeds the max.
+func CopyInPollFDs(t *kernel.Task, addr usermem.Addr, nfds uint) ([]linux.PollFD, error) {
+	if uint64(nfds) > t.ThreadGroup().Limits().GetCapped(limits.NumberOfFiles, fileCap) {
+		return nil, syserror.EINVAL
+	}
+
+	pfd := make([]linux.PollFD, nfds)
+	if nfds > 0 {
+		if _, err := t.CopyIn(addr, &pfd); err != nil {
+			return nil, err
+		}
+	}
+
+	return pfd, nil
+}
+
+func doPoll(t *kernel.Task, addr usermem.Addr, nfds uint, timeout time.Duration) (time.Duration, uintptr, error) {
+	pfd, err := CopyInPollFDs(t, addr, nfds)
+	if err != nil {
+		return timeout, 0, err
+	}
+
+	// Compatibility warning: Linux adds POLLHUP and POLLERR just before
+	// polling, in fs/select.c:do_pollfd(). Since pfd is copied out after
+	// polling, changing event masks here is an application-visible difference.
+	// (Linux also doesn't copy out event masks at all, only revents.)
+	for i := range pfd {
+		pfd[i].Events |= linux.POLLHUP | linux.POLLERR
+	}
+	remainingTimeout, n, err := pollBlock(t, pfd, timeout)
+	err = syserror.ConvertIntr(err, syserror.EINTR)
+
+	// The poll entries are copied out regardless of whether
+	// any are set or not. This aligns with the Linux behavior.
+	if nfds > 0 && err == nil {
+		if _, err := t.CopyOut(addr, pfd); err != nil {
+			return remainingTimeout, 0, err
+		}
+	}
+
+	return remainingTimeout, n, err
+}
+
+func doSelect(t *kernel.Task, nfds int, readFDs, writeFDs, exceptFDs usermem.Addr, timeout time.Duration) (uintptr, error) {
+	if nfds < 0 || nfds > fileCap {
+		return 0, syserror.EINVAL
+	}
+
+	// Capture all the provided input vectors.
+	//
+	// N.B. This only works on little-endian architectures.
+	byteCount := (nfds + 7) / 8
+
+	bitsInLastPartialByte := uint(nfds % 8)
+	r := make([]byte, byteCount)
+	w := make([]byte, byteCount)
+	e := make([]byte, byteCount)
+
+	if readFDs != 0 {
+		if _, err := t.CopyIn(readFDs, &r); err != nil {
+			return 0, err
+		}
+		// Mask out bits above nfds.
+		if bitsInLastPartialByte != 0 {
+			r[byteCount-1] &^= byte(0xff) << bitsInLastPartialByte
+		}
+	}
+
+	if writeFDs != 0 {
+		if _, err := t.CopyIn(writeFDs, &w); err != nil {
+			return 0, err
+		}
+		if bitsInLastPartialByte != 0 {
+			w[byteCount-1] &^= byte(0xff) << bitsInLastPartialByte
+		}
+	}
+
+	if exceptFDs != 0 {
+		if _, err := t.CopyIn(exceptFDs, &e); err != nil {
+			return 0, err
+		}
+		if bitsInLastPartialByte != 0 {
+			e[byteCount-1] &^= byte(0xff) << bitsInLastPartialByte
+		}
+	}
+
+	// Count how many FDs are actually being requested so that we can build
+	// a PollFD array.
+	fdCount := 0
+	for i := 0; i < byteCount; i++ {
+		v := r[i] | w[i] | e[i]
+		for v != 0 {
+			v &= (v - 1)
+			fdCount++
+		}
+	}
+
+	// Build the PollFD array.
+	pfd := make([]linux.PollFD, 0, fdCount)
+	var fd int32
+	for i := 0; i < byteCount; i++ {
+		rV, wV, eV := r[i], w[i], e[i]
+		v := rV | wV | eV
+		m := byte(1)
+		for j := 0; j < 8; j++ {
+			if (v & m) != 0 {
+				// Make sure the fd is valid and decrement the reference
+				// immediately to ensure we don't leak. Note, another thread
+				// might be about to close fd. This is racy, but that's
+				// OK. Linux is racy in the same way.
+				file := t.FDMap().GetFile(kdefs.FD(fd))
+				if file == nil {
+					return 0, syserror.EBADF
+				}
+				file.DecRef()
+
+				var mask int16
+				if (rV & m) != 0 {
+					mask |= selectReadEvents
+				}
+
+				if (wV & m) != 0 {
+					mask |= selectWriteEvents
+				}
+
+				if (eV & m) != 0 {
+					mask |= selectExceptEvents
+				}
+
+				pfd = append(pfd, linux.PollFD{
+					FD:     fd,
+					Events: mask,
+				})
+			}
+
+			fd++
+			m <<= 1
+		}
+	}
+
+	// Do the syscall, then count the number of bits set.
+	_, _, err := pollBlock(t, pfd, timeout)
+	if err != nil {
+		return 0, syserror.ConvertIntr(err, syserror.EINTR)
+	}
+
+	// r, w, and e are currently event mask bitsets; unset bits corresponding
+	// to events that *didn't* occur.
+	bitSetCount := uintptr(0)
+	for idx := range pfd {
+		events := pfd[idx].REvents
+		i, j := pfd[idx].FD/8, uint(pfd[idx].FD%8)
+		m := byte(1) << j
+		if r[i]&m != 0 {
+			if (events & selectReadEvents) != 0 {
+				bitSetCount++
+			} else {
+				r[i] &^= m
+			}
+		}
+		if w[i]&m != 0 {
+			if (events & selectWriteEvents) != 0 {
+				bitSetCount++
+			} else {
+				w[i] &^= m
+			}
+		}
+		if e[i]&m != 0 {
+			if (events & selectExceptEvents) != 0 {
+				bitSetCount++
+			} else {
+				e[i] &^= m
+			}
+		}
+	}
+
+	// Copy updated vectors back.
+	if readFDs != 0 {
+		if _, err := t.CopyOut(readFDs, r); err != nil {
+			return 0, err
+		}
+	}
+
+	if writeFDs != 0 {
+		if _, err := t.CopyOut(writeFDs, w); err != nil {
+			return 0, err
+		}
+	}
+
+	if exceptFDs != 0 {
+		if _, err := t.CopyOut(exceptFDs, e); err != nil {
+			return 0, err
+		}
+	}
+
+	return bitSetCount, nil
+}
+
+// timeoutRemaining returns the amount of time remaining for the specified
+// timeout or 0 if it has elapsed.
+//
+// startNs must be from CLOCK_MONOTONIC.
+func timeoutRemaining(t *kernel.Task, startNs ktime.Time, timeout time.Duration) time.Duration {
+	now := t.Kernel().MonotonicClock().Now()
+	remaining := timeout - now.Sub(startNs)
+	if remaining < 0 {
+		remaining = 0
+	}
+	return remaining
+}
+
+// copyOutTimespecRemaining copies the time remaining in timeout to timespecAddr.
+//
+// startNs must be from CLOCK_MONOTONIC.
+func copyOutTimespecRemaining(t *kernel.Task, startNs ktime.Time, timeout time.Duration, timespecAddr usermem.Addr) error {
+	if timeout <= 0 {
+		return nil
+	}
+	remaining := timeoutRemaining(t, startNs, timeout)
+	tsRemaining := linux.NsecToTimespec(remaining.Nanoseconds())
+	return copyTimespecOut(t, timespecAddr, &tsRemaining)
+}
+
+// copyOutTimevalRemaining copies the time remaining in timeout to timevalAddr.
+//
+// startNs must be from CLOCK_MONOTONIC.
+func copyOutTimevalRemaining(t *kernel.Task, startNs ktime.Time, timeout time.Duration, timevalAddr usermem.Addr) error {
+	if timeout <= 0 {
+		return nil
+	}
+	remaining := timeoutRemaining(t, startNs, timeout)
+	tvRemaining := linux.NsecToTimeval(remaining.Nanoseconds())
+	return copyTimevalOut(t, timevalAddr, &tvRemaining)
+}
+
+// pollRestartBlock encapsulates the state required to restart poll(2) via
+// restart_syscall(2).
+//
+// +stateify savable
+type pollRestartBlock struct {
+	pfdAddr usermem.Addr
+	nfds    uint
+	timeout time.Duration
+}
+
+// Restart implements kernel.SyscallRestartBlock.Restart.
+func (p *pollRestartBlock) Restart(t *kernel.Task) (uintptr, error) {
+	return poll(t, p.pfdAddr, p.nfds, p.timeout)
+}
+
+func poll(t *kernel.Task, pfdAddr usermem.Addr, nfds uint, timeout time.Duration) (uintptr, error) {
+	remainingTimeout, n, err := doPoll(t, pfdAddr, nfds, timeout)
+	// On an interrupt poll(2) is restarted with the remaining timeout.
+	if err == syserror.EINTR {
+		t.SetSyscallRestartBlock(&pollRestartBlock{
+			pfdAddr: pfdAddr,
+			nfds:    nfds,
+			timeout: remainingTimeout,
+		})
+		return 0, kernel.ERESTART_RESTARTBLOCK
+	}
+	return n, err
+}
+
+// Poll implements linux syscall poll(2).
+func Poll(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	pfdAddr := args[0].Pointer()
+	nfds := uint(args[1].Uint()) // poll(2) uses unsigned long.
+	timeout := time.Duration(args[2].Int()) * time.Millisecond
+	n, err := poll(t, pfdAddr, nfds, timeout)
+	return n, nil, err
+}
+
+// Ppoll implements linux syscall ppoll(2).
+func Ppoll(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	pfdAddr := args[0].Pointer()
+	nfds := uint(args[1].Uint()) // poll(2) uses unsigned long.
+	timespecAddr := args[2].Pointer()
+	maskAddr := args[3].Pointer()
+	maskSize := uint(args[4].Uint())
+
+	timeout, err := copyTimespecInToDuration(t, timespecAddr)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	var startNs ktime.Time
+	if timeout > 0 {
+		startNs = t.Kernel().MonotonicClock().Now()
+	}
+
+	if maskAddr != 0 {
+		mask, err := copyInSigSet(t, maskAddr, maskSize)
+		if err != nil {
+			return 0, nil, err
+		}
+
+		oldmask := t.SignalMask()
+		t.SetSignalMask(mask)
+		t.SetSavedSignalMask(oldmask)
+	}
+
+	_, n, err := doPoll(t, pfdAddr, nfds, timeout)
+	copyErr := copyOutTimespecRemaining(t, startNs, timeout, timespecAddr)
+	// doPoll returns EINTR if interrupted, but ppoll is normally restartable
+	// if interrupted by something other than a signal handled by the
+	// application (i.e. returns ERESTARTNOHAND). However, if
+	// copyOutTimespecRemaining failed, then the restarted ppoll would use the
+	// wrong timeout, so the error should be left as EINTR.
+	//
+	// Note that this means that if err is nil but copyErr is not, copyErr is
+	// ignored. This is consistent with Linux.
+	if err == syserror.EINTR && copyErr == nil {
+		err = kernel.ERESTARTNOHAND
+	}
+	return n, nil, err
+}
+
+// Select implements linux syscall select(2).
+func Select(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	nfds := int(args[0].Int()) // select(2) uses an int.
+	readFDs := args[1].Pointer()
+	writeFDs := args[2].Pointer()
+	exceptFDs := args[3].Pointer()
+	timevalAddr := args[4].Pointer()
+
+	// Use a negative Duration to indicate "no timeout".
+	timeout := time.Duration(-1)
+	if timevalAddr != 0 {
+		timeval, err := copyTimevalIn(t, timevalAddr)
+		if err != nil {
+			return 0, nil, err
+		}
+		if timeval.Sec < 0 || timeval.Usec < 0 {
+			return 0, nil, syserror.EINVAL
+		}
+		timeout = time.Duration(timeval.ToNsecCapped())
+	}
+	startNs := t.Kernel().MonotonicClock().Now()
+	n, err := doSelect(t, nfds, readFDs, writeFDs, exceptFDs, timeout)
+	copyErr := copyOutTimevalRemaining(t, startNs, timeout, timevalAddr)
+	// See comment in Ppoll.
+	if err == syserror.EINTR && copyErr == nil {
+		err = kernel.ERESTARTNOHAND
+	}
+	return n, nil, err
+}
+
+// Pselect implements linux syscall pselect(2).
+func Pselect(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	nfds := int(args[0].Int()) // select(2) uses an int.
+	readFDs := args[1].Pointer()
+	writeFDs := args[2].Pointer()
+	exceptFDs := args[3].Pointer()
+	timespecAddr := args[4].Pointer()
+	maskWithSizeAddr := args[5].Pointer()
+
+	timeout, err := copyTimespecInToDuration(t, timespecAddr)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	var startNs ktime.Time
+	if timeout > 0 {
+		startNs = t.Kernel().MonotonicClock().Now()
+	}
+
+	if maskWithSizeAddr != 0 {
+		maskAddr, size, err := copyInSigSetWithSize(t, maskWithSizeAddr)
+		if err != nil {
+			return 0, nil, err
+		}
+
+		if maskAddr != 0 {
+			mask, err := copyInSigSet(t, maskAddr, size)
+			if err != nil {
+				return 0, nil, err
+			}
+			oldmask := t.SignalMask()
+			t.SetSignalMask(mask)
+			t.SetSavedSignalMask(oldmask)
+		}
+	}
+
+	n, err := doSelect(t, nfds, readFDs, writeFDs, exceptFDs, timeout)
+	copyErr := copyOutTimespecRemaining(t, startNs, timeout, timespecAddr)
+	// See comment in Ppoll.
+	if err == syserror.EINTR && copyErr == nil {
+		err = kernel.ERESTARTNOHAND
+	}
+	return n, nil, err
+}