95 lines
2.5 KiB
Go
95 lines
2.5 KiB
Go
// Copyright 2019 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// +build linux
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package flipcall
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import (
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"fmt"
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"math"
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"sync/atomic"
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"syscall"
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"gvisor.dev/gvisor/pkg/abi/linux"
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"gvisor.dev/gvisor/pkg/log"
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)
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func (ep *Endpoint) doFutexRoundTrip() error {
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ourSeq, err := ep.doFutexNotifySeq()
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if err != nil {
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return err
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}
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return ep.doFutexWaitSeq(ourSeq)
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}
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func (ep *Endpoint) doFutexWaitFirst() error {
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return ep.doFutexWaitSeq(0)
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}
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func (ep *Endpoint) doFutexNotifyLast() error {
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_, err := ep.doFutexNotifySeq()
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return err
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}
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func (ep *Endpoint) doFutexNotifySeq() (uint32, error) {
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ourSeq := atomic.AddUint32(ep.seq(), 1)
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if err := ep.futexWake(1); err != nil {
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return ourSeq, fmt.Errorf("failed to FUTEX_WAKE peer Endpoint: %v", err)
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}
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return ourSeq, nil
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}
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func (ep *Endpoint) doFutexWaitSeq(prevSeq uint32) error {
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nextSeq := prevSeq + 1
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for {
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if ep.isShutdown() {
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return endpointShutdownError{}
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}
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if err := ep.futexWait(prevSeq); err != nil {
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return fmt.Errorf("failed to FUTEX_WAIT for peer Endpoint: %v", err)
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}
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seq := atomic.LoadUint32(ep.seq())
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if seq == nextSeq {
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return nil
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}
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if seq != prevSeq {
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return fmt.Errorf("invalid packet sequence number %d (expected %d or %d)", seq, prevSeq, nextSeq)
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}
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}
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}
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func (ep *Endpoint) doFutexInterruptForShutdown() {
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// Wake MaxInt32 threads to prevent a malicious or broken peer from
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// swallowing our wakeup by FUTEX_WAITing from multiple threads.
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if err := ep.futexWake(math.MaxInt32); err != nil {
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log.Warningf("failed to FUTEX_WAKE Endpoint: %v", err)
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}
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}
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func (ep *Endpoint) futexWake(numThreads int32) error {
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if _, _, e := syscall.RawSyscall(syscall.SYS_FUTEX, uintptr(ep.packet), linux.FUTEX_WAKE, uintptr(numThreads)); e != 0 {
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return e
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}
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return nil
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}
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func (ep *Endpoint) futexWait(seq uint32) error {
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_, _, e := syscall.Syscall6(syscall.SYS_FUTEX, uintptr(ep.packet), linux.FUTEX_WAIT, uintptr(seq), 0, 0, 0)
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if e != 0 && e != syscall.EAGAIN && e != syscall.EINTR {
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return e
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}
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return nil
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}
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