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