1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
|
// Copyright 2018 Google LLC
//
// 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/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/syscalls"
"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 = waiter.EventIn | waiter.EventHUp | waiter.EventErr
// selectWriteEvents is analogous to the Linux kernel's
// fs/select.c:POLLOUT_SET.
selectWriteEvents = waiter.EventOut | waiter.EventErr
// selectExceptEvents is analogous to the Linux kernel's
// fs/select.c:POLLEX_SET.
selectExceptEvents = waiter.EventPri
)
func doPoll(t *kernel.Task, pfdAddr usermem.Addr, nfds uint, timeout time.Duration) (time.Duration, uintptr, error) {
if uint64(nfds) > t.ThreadGroup().Limits().GetCapped(limits.NumberOfFiles, fileCap) {
return timeout, 0, syserror.EINVAL
}
pfd := make([]syscalls.PollFD, nfds)
if nfds > 0 {
if _, err := t.CopyIn(pfdAddr, &pfd); 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 |= waiter.EventHUp | waiter.EventErr
}
remainingTimeout, n, err := syscalls.Poll(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(pfdAddr, 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([]syscalls.PollFD, 0, fdCount)
fd := kdefs.FD(0)
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(fd)
if file == nil {
return 0, syserror.EBADF
}
file.DecRef()
mask := waiter.EventMask(0)
if (rV & m) != 0 {
mask |= selectReadEvents
}
if (wV & m) != 0 {
mask |= selectWriteEvents
}
if (eV & m) != 0 {
mask |= selectExceptEvents
}
pfd = append(pfd, syscalls.PollFD{
FD: fd,
Events: mask,
})
}
fd++
m <<= 1
}
}
// Do the syscall, then count the number of bits set.
_, _, err := syscalls.Poll(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
}
|