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// Copyright 2020 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 (
"gvisor.dev/gvisor/pkg/abi/linux"
"gvisor.dev/gvisor/pkg/errors/linuxerr"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/kernel"
"gvisor.dev/gvisor/pkg/usermem"
)
type vmReadWriteOp int
const (
localReadLocalWrite vmReadWriteOp = iota
remoteReadLocalWrite
localReadRemoteWrite
)
// ProcessVMReadv implements process_vm_readv(2).
func ProcessVMReadv(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
return processVMRW(t, args, false /*isWrite*/)
}
// ProcessVMWritev implements process_vm_writev(2).
func ProcessVMWritev(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
return processVMRW(t, args, true /*isWrite*/)
}
func processVMRW(t *kernel.Task, args arch.SyscallArguments, isWrite bool) (uintptr, *kernel.SyscallControl, error) {
pid := kernel.ThreadID(args[0].Int())
lvec := hostarch.Addr(args[1].Pointer())
liovcnt := int(args[2].Int64())
rvec := hostarch.Addr(args[3].Pointer())
riovcnt := int(args[4].Int64())
flags := args[5].Int()
switch {
case flags != 0 ||
liovcnt < 0 ||
riovcnt < 0 ||
liovcnt > linux.UIO_MAXIOV ||
riovcnt > linux.UIO_MAXIOV:
return 0, nil, linuxerr.EINVAL
case lvec == 0 || rvec == 0:
return 0, nil, linuxerr.EFAULT
case liovcnt == 0 || riovcnt == 0:
return 0, nil, nil
}
localProcess := t.ThreadGroup().Leader()
if localProcess == nil {
return 0, nil, linuxerr.ESRCH
}
remoteThreadGroup := localProcess.PIDNamespace().ThreadGroupWithID(pid)
if remoteThreadGroup == nil {
return 0, nil, linuxerr.ESRCH
}
remoteProcess := remoteThreadGroup.Leader()
isRemote := localProcess == remoteProcess
// For the write case, we read from the local process and write to the remote process.
op := localReadLocalWrite
if isWrite {
if isRemote {
op = remoteReadLocalWrite
}
return doProcessVMReadWrite(localProcess, remoteProcess, lvec, rvec, liovcnt, riovcnt, op)
}
// For the read case, we read from the remote process and write to the local process.
if isRemote {
op = localReadRemoteWrite
}
return doProcessVMReadWrite(remoteProcess, localProcess, rvec, lvec, riovcnt, liovcnt, op)
}
func doProcessVMReadWrite(rProcess, wProcess *kernel.Task, rAddr, wAddr hostarch.Addr, rIovecCount, wIovecCount int, op vmReadWriteOp) (uintptr, *kernel.SyscallControl, error) {
rCtx := rProcess.CopyContext(rProcess, usermem.IOOpts{})
wCtx := wProcess.CopyContext(wProcess, usermem.IOOpts{})
var wCount int
doProcessVMReadWriteMaybeLocked := func() error {
rIovecs, err := rCtx.CopyInIovecs(rAddr, rIovecCount)
if err != nil {
return err
}
wIovecs, err := wCtx.CopyInIovecs(wAddr, wIovecCount)
if err != nil {
return err
}
bufSize := 0
for _, rIovec := range rIovecs {
if int(rIovec.Length()) > bufSize {
bufSize = int(rIovec.Length())
}
}
var buf []byte
// We need to copy the called task's scratch buffer so we don't get a data race. If we are
// reading a remote process's memory, then we are on the writer's task goroutine, so use
// the write context's scratch buffer.
if op == remoteReadLocalWrite {
buf = wCtx.CopyScratchBuffer(bufSize)
} else {
buf = rCtx.CopyScratchBuffer(bufSize)
}
for _, rIovec := range rIovecs {
if len(wIovecs) <= 0 {
break
}
buf = buf[0:int(rIovec.Length())]
bytes, err := rCtx.CopyInBytes(rIovec.Start, buf)
if linuxerr.Equals(linuxerr.EFAULT, err) {
return nil
}
if err != nil {
return err
}
if bytes != int(rIovec.Length()) {
return nil
}
start := 0
for bytes > start && 0 < len(wIovecs) {
writeLength := int(wIovecs[0].Length())
if writeLength > (bytes - start) {
writeLength = bytes - start
}
out, err := wCtx.CopyOutBytes(wIovecs[0].Start, buf[start:writeLength+start])
wCount += out
start += out
if linuxerr.Equals(linuxerr.EFAULT, err) {
return nil
}
if err != nil {
return err
}
if out != writeLength {
return nil
}
wIovecs[0].Start += hostarch.Addr(out)
if !wIovecs[0].WellFormed() {
return err
}
if wIovecs[0].Length() == 0 {
wIovecs = wIovecs[1:]
}
}
}
return nil
}
var err error
switch op {
case remoteReadLocalWrite:
err = rCtx.WithTaskMutexLocked(doProcessVMReadWriteMaybeLocked)
case localReadRemoteWrite:
err = wCtx.WithTaskMutexLocked(doProcessVMReadWriteMaybeLocked)
case localReadLocalWrite:
// in the case of local reads/writes, we don't have to lock the task mutex, because we are
// running on the top of the task's goroutine already.
err = doProcessVMReadWriteMaybeLocked()
default:
panic("unsupported operation passed")
}
return uintptr(wCount), nil, err
}
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