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
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
|
/* Linux-specific ptrace manipulation routines.
Copyright (C) 2012-2013 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifdef GDBSERVER
#include "server.h"
#else
#include "defs.h"
#include "gdb_string.h"
#endif
#include "linux-ptrace.h"
#include "linux-procfs.h"
#include "nat/linux-waitpid.h"
#include "buffer.h"
#include "gdb_assert.h"
#include "gdb_wait.h"
/* Stores the currently supported ptrace options. A value of
-1 means we did not check for features yet. A value of 0 means
there are no supported features. */
static int current_ptrace_options = -1;
/* Find all possible reasons we could fail to attach PID and append these
newline terminated reason strings to initialized BUFFER. '\0' termination
of BUFFER must be done by the caller. */
void
linux_ptrace_attach_warnings (pid_t pid, struct buffer *buffer)
{
pid_t tracerpid;
tracerpid = linux_proc_get_tracerpid (pid);
if (tracerpid > 0)
buffer_xml_printf (buffer, _("warning: process %d is already traced "
"by process %d\n"),
(int) pid, (int) tracerpid);
if (linux_proc_pid_is_zombie (pid))
buffer_xml_printf (buffer, _("warning: process %d is a zombie "
"- the process has already terminated\n"),
(int) pid);
}
#if defined __i386__ || defined __x86_64__
/* Address of the 'ret' instruction in asm code block below. */
extern void (linux_ptrace_test_ret_to_nx_instr) (void);
#include <sys/reg.h>
#include <sys/mman.h>
#include <signal.h>
#include <stdint.h>
#endif /* defined __i386__ || defined __x86_64__ */
/* Test broken off-trunk Linux kernel patchset for NX support on i386. It was
removed in Fedora kernel 88fa1f0332d188795ed73d7ac2b1564e11a0b4cd.
Test also x86_64 arch for PaX support. */
static void
linux_ptrace_test_ret_to_nx (void)
{
#if defined __i386__ || defined __x86_64__
pid_t child, got_pid;
gdb_byte *return_address, *pc;
long l;
int status, kill_status;
return_address = mmap (NULL, 2, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (return_address == MAP_FAILED)
{
warning (_("linux_ptrace_test_ret_to_nx: Cannot mmap: %s"),
strerror (errno));
return;
}
/* Put there 'int3'. */
*return_address = 0xcc;
child = fork ();
switch (child)
{
case -1:
warning (_("linux_ptrace_test_ret_to_nx: Cannot fork: %s"),
strerror (errno));
return;
case 0:
l = ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) NULL,
(PTRACE_TYPE_ARG4) NULL);
if (l != 0)
warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_TRACEME: %s"),
strerror (errno));
else
{
#if defined __i386__
asm volatile ("pushl %0;"
".globl linux_ptrace_test_ret_to_nx_instr;"
"linux_ptrace_test_ret_to_nx_instr:"
"ret"
: : "r" (return_address) : "%esp", "memory");
#elif defined __x86_64__
asm volatile ("pushq %0;"
".globl linux_ptrace_test_ret_to_nx_instr;"
"linux_ptrace_test_ret_to_nx_instr:"
"ret"
: : "r" ((uint64_t) (uintptr_t) return_address)
: "%rsp", "memory");
#else
# error "!__i386__ && !__x86_64__"
#endif
gdb_assert_not_reached ("asm block did not terminate");
}
_exit (1);
}
errno = 0;
got_pid = waitpid (child, &status, 0);
if (got_pid != child)
{
warning (_("linux_ptrace_test_ret_to_nx: waitpid returned %ld: %s"),
(long) got_pid, strerror (errno));
return;
}
if (WIFSIGNALED (status))
{
if (WTERMSIG (status) != SIGKILL)
warning (_("linux_ptrace_test_ret_to_nx: WTERMSIG %d is not SIGKILL!"),
(int) WTERMSIG (status));
else
warning (_("Cannot call inferior functions, Linux kernel PaX "
"protection forbids return to non-executable pages!"));
return;
}
if (!WIFSTOPPED (status))
{
warning (_("linux_ptrace_test_ret_to_nx: status %d is not WIFSTOPPED!"),
status);
return;
}
/* We may get SIGSEGV due to missing PROT_EXEC of the return_address. */
if (WSTOPSIG (status) != SIGTRAP && WSTOPSIG (status) != SIGSEGV)
{
warning (_("linux_ptrace_test_ret_to_nx: "
"WSTOPSIG %d is neither SIGTRAP nor SIGSEGV!"),
(int) WSTOPSIG (status));
return;
}
errno = 0;
#if defined __i386__
l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (EIP * 4),
(PTRACE_TYPE_ARG4) NULL);
#elif defined __x86_64__
l = ptrace (PTRACE_PEEKUSER, child, (PTRACE_TYPE_ARG3) (uintptr_t) (RIP * 8),
(PTRACE_TYPE_ARG4) NULL);
#else
# error "!__i386__ && !__x86_64__"
#endif
if (errno != 0)
{
warning (_("linux_ptrace_test_ret_to_nx: Cannot PTRACE_PEEKUSER: %s"),
strerror (errno));
return;
}
pc = (void *) (uintptr_t) l;
kill (child, SIGKILL);
ptrace (PTRACE_KILL, child, (PTRACE_TYPE_ARG3) NULL,
(PTRACE_TYPE_ARG4) NULL);
errno = 0;
got_pid = waitpid (child, &kill_status, 0);
if (got_pid != child)
{
warning (_("linux_ptrace_test_ret_to_nx: "
"PTRACE_KILL waitpid returned %ld: %s"),
(long) got_pid, strerror (errno));
return;
}
if (!WIFSIGNALED (kill_status))
{
warning (_("linux_ptrace_test_ret_to_nx: "
"PTRACE_KILL status %d is not WIFSIGNALED!"),
status);
return;
}
/* + 1 is there as x86* stops after the 'int3' instruction. */
if (WSTOPSIG (status) == SIGTRAP && pc == return_address + 1)
{
/* PASS */
return;
}
/* We may get SIGSEGV due to missing PROT_EXEC of the RETURN_ADDRESS page. */
if (WSTOPSIG (status) == SIGSEGV && pc == return_address)
{
/* PASS */
return;
}
if ((void (*) (void)) pc != &linux_ptrace_test_ret_to_nx_instr)
warning (_("linux_ptrace_test_ret_to_nx: PC %p is neither near return "
"address %p nor is the return instruction %p!"),
pc, return_address, &linux_ptrace_test_ret_to_nx_instr);
else
warning (_("Cannot call inferior functions on this system - "
"Linux kernel with broken i386 NX (non-executable pages) "
"support detected!"));
#endif /* defined __i386__ || defined __x86_64__ */
}
/* Helper function to fork a process and make the child process call
the function FUNCTION, passing CHILD_STACK as parameter.
For MMU-less targets, clone is used instead of fork, and
CHILD_STACK is used as stack space for the cloned child. If NULL,
stack space is allocated via malloc (and subsequently passed to
FUNCTION). For MMU targets, CHILD_STACK is ignored. */
static int
linux_fork_to_function (gdb_byte *child_stack, void (*function) (gdb_byte *))
{
int child_pid;
/* Sanity check the function pointer. */
gdb_assert (function != NULL);
#if defined(__UCLIBC__) && defined(HAS_NOMMU)
#define STACK_SIZE 4096
if (child_stack == NULL)
child_stack = xmalloc (STACK_SIZE * 4);
/* Use CLONE_VM instead of fork, to support uClinux (no MMU). */
#ifdef __ia64__
child_pid = __clone2 (function, child_stack, STACK_SIZE,
CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2);
#else /* !__ia64__ */
child_pid = clone (function, child_stack + STACK_SIZE,
CLONE_VM | SIGCHLD, child_stack + STACK_SIZE * 2);
#endif /* !__ia64__ */
#else /* !defined(__UCLIBC) && defined(HAS_NOMMU) */
child_pid = fork ();
if (child_pid == 0)
function (NULL);
#endif /* defined(__UCLIBC) && defined(HAS_NOMMU) */
if (child_pid == -1)
perror_with_name (("fork"));
return child_pid;
}
/* A helper function for linux_check_ptrace_features, called after
the child forks a grandchild. */
static void
linux_grandchild_function (gdb_byte *child_stack)
{
/* Free any allocated stack. */
xfree (child_stack);
/* This code is only reacheable by the grandchild (child's child)
process. */
_exit (0);
}
/* A helper function for linux_check_ptrace_features, called after
the parent process forks a child. The child allows itself to
be traced by its parent. */
static void
linux_child_function (gdb_byte *child_stack)
{
ptrace (PTRACE_TRACEME, 0, (PTRACE_TYPE_ARG3) 0, (PTRACE_TYPE_ARG4) 0);
kill (getpid (), SIGSTOP);
/* Fork a grandchild. */
linux_fork_to_function (child_stack, linux_grandchild_function);
/* This code is only reacheable by the child (grandchild's parent)
process. */
_exit (0);
}
/* Determine ptrace features available on this target. */
static void
linux_check_ptrace_features (void)
{
int child_pid, ret, status;
long second_pid;
/* Initialize the options. */
current_ptrace_options = 0;
/* Fork a child so we can do some testing. The child will call
linux_child_function and will get traced. The child will
eventually fork a grandchild so we can test fork event
reporting. */
child_pid = linux_fork_to_function (NULL, linux_child_function);
ret = my_waitpid (child_pid, &status, 0);
if (ret == -1)
perror_with_name (("waitpid"));
else if (ret != child_pid)
error (_("linux_check_ptrace_features: waitpid: unexpected result %d."),
ret);
if (! WIFSTOPPED (status))
error (_("linux_check_ptrace_features: waitpid: unexpected status %d."),
status);
/* First, set the PTRACE_O_TRACEFORK option. If this fails, we
know for sure that it is not supported. */
ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) PTRACE_O_TRACEFORK);
if (ret != 0)
{
ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
{
warning (_("linux_check_ptrace_features: failed to kill child"));
return;
}
ret = my_waitpid (child_pid, &status, 0);
if (ret != child_pid)
warning (_("linux_check_ptrace_features: failed "
"to wait for killed child"));
else if (!WIFSIGNALED (status))
warning (_("linux_check_ptrace_features: unexpected "
"wait status 0x%x from killed child"), status);
return;
}
#ifdef GDBSERVER
/* gdbserver does not support PTRACE_O_TRACESYSGOOD or
PTRACE_O_TRACEVFORKDONE yet. */
#else
/* Check if the target supports PTRACE_O_TRACESYSGOOD. */
ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) PTRACE_O_TRACESYSGOOD);
if (ret == 0)
current_ptrace_options |= PTRACE_O_TRACESYSGOOD;
/* Check if the target supports PTRACE_O_TRACEVFORKDONE. */
ret = ptrace (PTRACE_SETOPTIONS, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) (PTRACE_O_TRACEFORK
| PTRACE_O_TRACEVFORKDONE));
if (ret == 0)
current_ptrace_options |= PTRACE_O_TRACEVFORKDONE;
#endif
/* Setting PTRACE_O_TRACEFORK did not cause an error, however we
don't know for sure that the feature is available; old
versions of PTRACE_SETOPTIONS ignored unknown options.
Therefore, we attach to the child process, use PTRACE_SETOPTIONS
to enable fork tracing, and let it fork. If the process exits,
we assume that we can't use PTRACE_O_TRACEFORK; if we get the
fork notification, and we can extract the new child's PID, then
we assume that we can.
We do not explicitly check for vfork tracing here. It is
assumed that vfork tracing is available whenever fork tracing
is available. */
ret = ptrace (PTRACE_CONT, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
warning (_("linux_check_ptrace_features: failed to resume child"));
ret = my_waitpid (child_pid, &status, 0);
/* Check if we received a fork event notification. */
if (ret == child_pid && WIFSTOPPED (status)
&& status >> 16 == PTRACE_EVENT_FORK)
{
/* We did receive a fork event notification. Make sure its PID
is reported. */
second_pid = 0;
ret = ptrace (PTRACE_GETEVENTMSG, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) &second_pid);
if (ret == 0 && second_pid != 0)
{
int second_status;
/* We got the PID from the grandchild, which means fork
tracing is supported. */
#ifdef GDBSERVER
/* Do not enable all the options for now since gdbserver does not
properly support them. This restriction will be lifted when
gdbserver is augmented to support them. */
current_ptrace_options |= PTRACE_O_TRACECLONE;
#else
current_ptrace_options |= PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK
| PTRACE_O_TRACECLONE | PTRACE_O_TRACEEXEC;
/* Do not enable PTRACE_O_TRACEEXIT until GDB is more prepared to
support read-only process state. */
#endif
/* Do some cleanup and kill the grandchild. */
my_waitpid (second_pid, &second_status, 0);
ret = ptrace (PTRACE_KILL, second_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
warning (_("linux_check_ptrace_features: "
"failed to kill second child"));
my_waitpid (second_pid, &status, 0);
}
}
else
warning (_("linux_check_ptrace_features: unexpected result from waitpid "
"(%d, status 0x%x)"), ret, status);
/* Clean things up and kill any pending children. */
do
{
ret = ptrace (PTRACE_KILL, child_pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) 0);
if (ret != 0)
warning ("linux_check_ptrace_features: failed to kill child");
my_waitpid (child_pid, &status, 0);
}
while (WIFSTOPPED (status));
}
/* Enable reporting of all currently supported ptrace events. */
void
linux_enable_event_reporting (pid_t pid)
{
/* Check if we have initialized the ptrace features for this
target. If not, do it now. */
if (current_ptrace_options == -1)
linux_check_ptrace_features ();
/* Set the options. */
ptrace (PTRACE_SETOPTIONS, pid, (PTRACE_TYPE_ARG3) 0,
(PTRACE_TYPE_ARG4) (uintptr_t) current_ptrace_options);
}
/* Returns non-zero if PTRACE_OPTIONS is contained within
CURRENT_PTRACE_OPTIONS, therefore supported. Returns 0
otherwise. */
static int
ptrace_supports_feature (int ptrace_options)
{
gdb_assert (current_ptrace_options >= 0);
return ((current_ptrace_options & ptrace_options) == ptrace_options);
}
/* Returns non-zero if PTRACE_EVENT_FORK is supported by ptrace,
0 otherwise. Note that if PTRACE_EVENT_FORK is supported so is
PTRACE_EVENT_CLONE, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
since they were all added to the kernel at the same time. */
int
linux_supports_tracefork (void)
{
return ptrace_supports_feature (PTRACE_O_TRACEFORK);
}
/* Returns non-zero if PTRACE_EVENT_CLONE is supported by ptrace,
0 otherwise. Note that if PTRACE_EVENT_CLONE is supported so is
PTRACE_EVENT_FORK, PTRACE_EVENT_EXEC and PTRACE_EVENT_VFORK,
since they were all added to the kernel at the same time. */
int
linux_supports_traceclone (void)
{
return ptrace_supports_feature (PTRACE_O_TRACECLONE);
}
/* Returns non-zero if PTRACE_O_TRACEVFORKDONE is supported by
ptrace, 0 otherwise. */
int
linux_supports_tracevforkdone (void)
{
return ptrace_supports_feature (PTRACE_O_TRACEVFORKDONE);
}
/* Returns non-zero if PTRACE_O_TRACESYSGOOD is supported by ptrace,
0 otherwise. */
int
linux_supports_tracesysgood (void)
{
return ptrace_supports_feature (PTRACE_O_TRACESYSGOOD);
}
/* Display possible problems on this system. Display them only once per GDB
execution. */
void
linux_ptrace_init_warnings (void)
{
static int warned = 0;
if (warned)
return;
warned = 1;
linux_ptrace_test_ret_to_nx ();
}
|