119 lines
4.0 KiB
Go
119 lines
4.0 KiB
Go
// Copyright 2018 Google Inc.
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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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package kernel
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import (
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"gvisor.googlesource.com/gvisor/pkg/sentry/hostcpu"
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"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
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"gvisor.googlesource.com/gvisor/pkg/syserror"
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)
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// Restartable sequences, as described in https://lwn.net/Articles/650333/.
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// RSEQCriticalRegion describes a restartable sequence critical region.
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type RSEQCriticalRegion struct {
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// When a task in this thread group has its CPU preempted (as defined by
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// platform.ErrContextCPUPreempted) or has a signal delivered to an
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// application handler while its instruction pointer is in CriticalSection,
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// set the instruction pointer to Restart and application register r10 (on
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// amd64) to the former instruction pointer.
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CriticalSection usermem.AddrRange
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Restart usermem.Addr
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}
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// RSEQAvailable returns true if t supports restartable sequences.
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func (t *Task) RSEQAvailable() bool {
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return t.k.useHostCores && t.k.Platform.DetectsCPUPreemption()
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}
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// RSEQCriticalRegion returns a copy of t's thread group's current restartable
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// sequence.
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func (t *Task) RSEQCriticalRegion() RSEQCriticalRegion {
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return *t.tg.rscr.Load().(*RSEQCriticalRegion)
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}
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// SetRSEQCriticalRegion replaces t's thread group's restartable sequence.
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//
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// Preconditions: t.RSEQAvailable() == true.
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func (t *Task) SetRSEQCriticalRegion(rscr RSEQCriticalRegion) error {
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// These checks are somewhat more lenient than in Linux, which (bizarrely)
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// requires rscr.CriticalSection to be non-empty and rscr.Restart to be
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// outside of rscr.CriticalSection, even if rscr.CriticalSection.Start == 0
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// (which disables the critical region).
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if rscr.CriticalSection.Start == 0 {
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rscr.CriticalSection.End = 0
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rscr.Restart = 0
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t.tg.rscr.Store(&rscr)
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return nil
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}
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if rscr.CriticalSection.Start >= rscr.CriticalSection.End {
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return syserror.EINVAL
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}
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if rscr.CriticalSection.Contains(rscr.Restart) {
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return syserror.EINVAL
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}
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// TODO: check that rscr.CriticalSection and rscr.Restart are in
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// the application address range, for consistency with Linux
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t.tg.rscr.Store(&rscr)
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return nil
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}
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// RSEQCPUAddr returns the address that RSEQ will keep updated with t's CPU
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// number.
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//
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// Preconditions: The caller must be running on the task goroutine.
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func (t *Task) RSEQCPUAddr() usermem.Addr {
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return t.rseqCPUAddr
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}
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// SetRSEQCPUAddr replaces the address that RSEQ will keep updated with t's CPU
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// number.
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//
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// Preconditions: t.RSEQAvailable() == true. The caller must be running on the
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// task goroutine. t's AddressSpace must be active.
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func (t *Task) SetRSEQCPUAddr(addr usermem.Addr) error {
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t.rseqCPUAddr = addr
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if addr != 0 {
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if err := t.rseqCopyOutCPU(); err != nil {
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t.rseqCPUAddr = 0
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t.rseqCPU = -1
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return syserror.EINVAL // yes, EINVAL, not err or EFAULT
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}
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} else {
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t.rseqCPU = -1
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}
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return nil
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}
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// Preconditions: The caller must be running on the task goroutine. t's
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// AddressSpace must be active.
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func (t *Task) rseqCopyOutCPU() error {
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t.rseqCPU = int32(hostcpu.GetCPU())
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buf := t.CopyScratchBuffer(4)
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usermem.ByteOrder.PutUint32(buf, uint32(t.rseqCPU))
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_, err := t.CopyOutBytes(t.rseqCPUAddr, buf)
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return err
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}
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// Preconditions: The caller must be running on the task goroutine.
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func (t *Task) rseqInterrupt() {
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rscr := t.tg.rscr.Load().(*RSEQCriticalRegion)
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if ip := t.Arch().IP(); rscr.CriticalSection.Contains(usermem.Addr(ip)) {
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t.Debugf("Interrupted RSEQ critical section at %#x; restarting at %#x", ip, rscr.Restart)
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t.Arch().SetIP(uintptr(rscr.Restart))
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t.Arch().SetRSEQInterruptedIP(ip)
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}
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}
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