aboutsummaryrefslogtreecommitdiff
path: root/src/client/linux/handler/exception_handler.cc
blob: 5d9e93f7f799b185b293bf28ca5f28a3faded64b (plain)
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
// Copyright (c) 2010 Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// The ExceptionHandler object installs signal handlers for a number of
// signals. We rely on the signal handler running on the thread which crashed
// in order to identify it. This is true of the synchronous signals (SEGV etc),
// but not true of ABRT. Thus, if you send ABRT to yourself in a program which
// uses ExceptionHandler, you need to use tgkill to direct it to the current
// thread.
//
// The signal flow looks like this:
//
//   SignalHandler (uses a global stack of ExceptionHandler objects to find
//        |         one to handle the signal. If the first rejects it, try
//        |         the second etc...)
//        V
//   HandleSignal ----------------------------| (clones a new process which
//        |                                   |  shares an address space with
//   (wait for cloned                         |  the crashed process. This
//     process)                               |  allows us to ptrace the crashed
//        |                                   |  process)
//        V                                   V
//   (set signal handler to             ThreadEntry (static function to bounce
//    SIG_DFL and rethrow,                    |      back into the object)
//    killing the crashed                     |
//    process)                                V
//                                          DoDump  (writes minidump)
//                                            |
//                                            V
//                                         sys_exit
//

// This code is a little fragmented. Different functions of the ExceptionHandler
// class run in a number of different contexts. Some of them run in a normal
// context and are easy to code, others run in a compromised context and the
// restrictions at the top of minidump_writer.cc apply: no libc and use the
// alternative malloc. Each function should have comment above it detailing the
// context which it runs in.

#include "client/linux/handler/exception_handler.h"

#include <errno.h>
#include <fcntl.h>
#include <linux/limits.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/wait.h>
#include <unistd.h>

#if !defined(__ANDROID__)
#include <sys/signal.h>
#include <sys/ucontext.h>
#include <sys/user.h>
#include <ucontext.h>
#endif

#include <algorithm>
#include <utility>
#include <vector>

#include "common/linux/linux_libc_support.h"
#include "common/memory.h"
#include "client/linux/log/log.h"
#include "client/linux/minidump_writer/linux_dumper.h"
#include "client/linux/minidump_writer/minidump_writer.h"
#include "common/linux/guid_creator.h"
#include "common/linux/eintr_wrapper.h"
#include "third_party/lss/linux_syscall_support.h"

#include "linux/sched.h"

#ifndef PR_SET_PTRACER
#define PR_SET_PTRACER 0x59616d61
#endif

// A wrapper for the tgkill syscall: send a signal to a specific thread.
static int tgkill(pid_t tgid, pid_t tid, int sig) {
  return syscall(__NR_tgkill, tgid, tid, sig);
  return 0;
}

namespace google_breakpad {

// The list of signals which we consider to be crashes. The default action for
// all these signals must be Core (see man 7 signal) because we rethrow the
// signal after handling it and expect that it'll be fatal.
static const int kExceptionSignals[] = {
  SIGSEGV, SIGABRT, SIGFPE, SIGILL, SIGBUS, -1
};

// We can stack multiple exception handlers. In that case, this is the global
// which holds the stack.
std::vector<ExceptionHandler*>* ExceptionHandler::handler_stack_ = NULL;
unsigned ExceptionHandler::handler_stack_index_ = 0;
pthread_mutex_t ExceptionHandler::handler_stack_mutex_ =
    PTHREAD_MUTEX_INITIALIZER;

// Runs before crashing: normal context.
ExceptionHandler::ExceptionHandler(const std::string &dump_path,
                                   FilterCallback filter,
                                   MinidumpCallback callback,
                                   void *callback_context,
                                   bool install_handler)
  : filter_(filter),
    callback_(callback),
    callback_context_(callback_context),
    handler_installed_(install_handler)
{
  Init(dump_path, -1);
}

ExceptionHandler::ExceptionHandler(const std::string &dump_path,
                                   FilterCallback filter,
                                   MinidumpCallback callback,
                                   void* callback_context,
                                   bool install_handler,
                                   const int server_fd)
  : filter_(filter),
    callback_(callback),
    callback_context_(callback_context),
    handler_installed_(install_handler)
{
  Init(dump_path, server_fd);
}

// Runs before crashing: normal context.
ExceptionHandler::~ExceptionHandler() {
  UninstallHandlers();
}

void ExceptionHandler::Init(const std::string &dump_path,
                            const int server_fd)
{
  crash_handler_ = NULL;
  if (0 <= server_fd)
    crash_generation_client_
      .reset(CrashGenerationClient::TryCreate(server_fd));

  if (handler_installed_)
    InstallHandlers();

  if (!IsOutOfProcess())
    set_dump_path(dump_path);

  pthread_mutex_lock(&handler_stack_mutex_);
  if (handler_stack_ == NULL)
    handler_stack_ = new std::vector<ExceptionHandler *>;
  handler_stack_->push_back(this);
  pthread_mutex_unlock(&handler_stack_mutex_);
}

// Runs before crashing: normal context.
bool ExceptionHandler::InstallHandlers() {
  // We run the signal handlers on an alternative stack because we might have
  // crashed because of a stack overflow.

  // We use this value rather than SIGSTKSZ because we would end up overrunning
  // such a small stack.
  static const unsigned kSigStackSize = 8192;

  stack_t stack;
  // Only set an alternative stack if there isn't already one, or if the current
  // one is too small.
  if (sys_sigaltstack(NULL, &stack) == -1 || !stack.ss_sp ||
      stack.ss_size < kSigStackSize) {
    memset(&stack, 0, sizeof(stack));
    stack.ss_sp = malloc(kSigStackSize);
    stack.ss_size = kSigStackSize;

    if (sys_sigaltstack(&stack, NULL) == -1)
      return false;
  }

  struct sigaction sa;
  memset(&sa, 0, sizeof(sa));
  sigemptyset(&sa.sa_mask);

  // mask all exception signals when we're handling one of them.
  for (unsigned i = 0; kExceptionSignals[i] != -1; ++i)
    sigaddset(&sa.sa_mask, kExceptionSignals[i]);

  sa.sa_sigaction = SignalHandler;
  sa.sa_flags = SA_ONSTACK | SA_SIGINFO;

  for (unsigned i = 0; kExceptionSignals[i] != -1; ++i) {
    struct sigaction* old = new struct sigaction;
    if (sigaction(kExceptionSignals[i], &sa, old) == -1)
      return false;
    old_handlers_.push_back(std::make_pair(kExceptionSignals[i], old));
  }
  return true;
}

// Runs before crashing: normal context.
void ExceptionHandler::UninstallHandlers() {
  for (unsigned i = 0; i < old_handlers_.size(); ++i) {
    struct sigaction *action =
        reinterpret_cast<struct sigaction*>(old_handlers_[i].second);
    sigaction(old_handlers_[i].first, action, NULL);
    delete action;
  }
  pthread_mutex_lock(&handler_stack_mutex_);
  std::vector<ExceptionHandler*>::iterator handler =
      std::find(handler_stack_->begin(), handler_stack_->end(), this);
  handler_stack_->erase(handler);
  pthread_mutex_unlock(&handler_stack_mutex_);
  old_handlers_.clear();
}

// Runs before crashing: normal context.
void ExceptionHandler::UpdateNextID() {
  GUID guid;
  char guid_str[kGUIDStringLength + 1];
  if (CreateGUID(&guid) && GUIDToString(&guid, guid_str, sizeof(guid_str))) {
    next_minidump_id_ = guid_str;
    next_minidump_id_c_ = next_minidump_id_.c_str();

    char minidump_path[PATH_MAX];
    snprintf(minidump_path, sizeof(minidump_path), "%s/%s.dmp",
             dump_path_c_,
             guid_str);

    next_minidump_path_ = minidump_path;
    next_minidump_path_c_ = next_minidump_path_.c_str();
  }
}

// void ExceptionHandler::set_crash_handler(HandlerCallback callback) {
//   crash_handler_ = callback;
// }

// This function runs in a compromised context: see the top of the file.
// Runs on the crashing thread.
// static
void ExceptionHandler::SignalHandler(int sig, siginfo_t* info, void* uc) {
  // All the exception signals are blocked at this point.
  pthread_mutex_lock(&handler_stack_mutex_);

  if (!handler_stack_->size()) {
    pthread_mutex_unlock(&handler_stack_mutex_);
    return;
  }

  for (int i = handler_stack_->size() - 1; i >= 0; --i) {
    if ((*handler_stack_)[i]->HandleSignal(sig, info, uc)) {
      // successfully handled: We are in an invalid state since an exception
      // signal has been delivered. We don't call the exit handlers because
      // they could end up corrupting on-disk state.
      break;
    }
  }

  pthread_mutex_unlock(&handler_stack_mutex_);

  if (info->si_pid) {
    // This signal was triggered by somebody sending us the signal with kill().
    // In order to retrigger it, we have to queue a new signal by calling
    // kill() ourselves.
    if (tgkill(getpid(), syscall(__NR_gettid), sig) < 0) {
      // If we failed to kill ourselves (e.g. because a sandbox disallows us
      // to do so), we instead resort to terminating our process. This will
      // result in an incorrect exit code.
      _exit(1);
    }
  } else {
    // This was a synchronous signal triggered by a hard fault (e.g. SIGSEGV).
    // No need to reissue the signal. It will automatically trigger again,
    // when we return from the signal handler.
  }

  // As soon as we return from the signal handler, our signal will become
  // unmasked. At that time, we will  get terminated with the same signal that
  // was triggered originally. This allows our parent to know that we crashed.
  // The default action for all the signals which we catch is Core, so
  // this is the end of us.
  signal(sig, SIG_DFL);
}

struct ThreadArgument {
  pid_t pid;  // the crashing process
  ExceptionHandler* handler;
  const void* context;  // a CrashContext structure
  size_t context_size;
};

// This is the entry function for the cloned process. We are in a compromised
// context here: see the top of the file.
// static
int ExceptionHandler::ThreadEntry(void *arg) {
  const ThreadArgument *thread_arg = reinterpret_cast<ThreadArgument*>(arg);

  // Block here until the crashing process unblocks us when
  // we're allowed to use ptrace
  thread_arg->handler->WaitForContinueSignal();

  return thread_arg->handler->DoDump(thread_arg->pid, thread_arg->context,
                                     thread_arg->context_size) == false;
}

// This function runs in a compromised context: see the top of the file.
// Runs on the crashing thread.
bool ExceptionHandler::HandleSignal(int sig, siginfo_t* info, void* uc) {
  if (filter_ && !filter_(callback_context_))
    return false;

  // Allow ourselves to be dumped if the signal is trusted.
  bool signal_trusted = info->si_code > 0;
  bool signal_pid_trusted = info->si_code == SI_USER ||
      info->si_code == SI_TKILL;
  if (signal_trusted || (signal_pid_trusted && info->si_pid == getpid())) {
    sys_prctl(PR_SET_DUMPABLE, 1);
  }
  CrashContext context;
  memcpy(&context.siginfo, info, sizeof(siginfo_t));
  memcpy(&context.context, uc, sizeof(struct ucontext));
#if !defined(__ARM_EABI__)
  // FP state is not part of user ABI on ARM Linux.
  struct ucontext *uc_ptr = (struct ucontext*)uc;
  if (uc_ptr->uc_mcontext.fpregs) {
    memcpy(&context.float_state,
           uc_ptr->uc_mcontext.fpregs,
           sizeof(context.float_state));
  }
#endif
  context.tid = syscall(__NR_gettid);
  if (crash_handler_ != NULL) {
    if (crash_handler_(&context, sizeof(context),
                       callback_context_)) {
      return true;
    }
  }
  return GenerateDump(&context);
}

// This function may run in a compromised context: see the top of the file.
bool ExceptionHandler::GenerateDump(CrashContext *context) {
  if (IsOutOfProcess())
    return crash_generation_client_->RequestDump(context, sizeof(*context));

  static const unsigned kChildStackSize = 8000;
  PageAllocator allocator;
  uint8_t* stack = (uint8_t*) allocator.Alloc(kChildStackSize);
  if (!stack)
    return false;
  // clone() needs the top-most address. (scrub just to be safe)
  stack += kChildStackSize;
  my_memset(stack - 16, 0, 16);

  ThreadArgument thread_arg;
  thread_arg.handler = this;
  thread_arg.pid = getpid();
  thread_arg.context = context;
  thread_arg.context_size = sizeof(*context);

  // We need to explicitly enable ptrace of parent processes on some
  // kernels, but we need to know the PID of the cloned process before we
  // can do this. Create a pipe here which we can use to block the
  // cloned process after creating it, until we have explicitly enabled ptrace
  if(sys_pipe(fdes) == -1) {
    // Creating the pipe failed. We'll log an error but carry on anyway,
    // as we'll probably still get a useful crash report. All that will happen
    // is the write() and read() calls will fail with EBADF
    static const char no_pipe_msg[] = "ExceptionHandler::GenerateDump \
                                       sys_pipe failed:";
    logger::write(no_pipe_msg, sizeof(no_pipe_msg) - 1);
    logger::write(strerror(errno), strlen(strerror(errno)));
    logger::write("\n", 1);
  }

#if defined(__ANDROID__)
  const pid_t child = clone(
      ThreadEntry, stack, CLONE_FILES | CLONE_FS | CLONE_UNTRACED,
      &thread_arg);
#else
  const pid_t child = sys_clone(
      ThreadEntry, stack, CLONE_FILES | CLONE_FS | CLONE_UNTRACED,
      &thread_arg, NULL, NULL, NULL);
#endif
  int r, status;
  // Allow the child to ptrace us
  sys_prctl(PR_SET_PTRACER, child);
  SendContinueSignalToChild();
  do {
    r = sys_waitpid(child, &status, __WALL);
  } while (r == -1 && errno == EINTR);

  sys_close(fdes[0]);
  sys_close(fdes[1]);

  if (r == -1) {
    static const char msg[] = "ExceptionHandler::GenerateDump waitpid failed:";
    logger::write(msg, sizeof(msg) - 1);
    logger::write(strerror(errno), strlen(strerror(errno)));
    logger::write("\n", 1);
  }

  bool success = r != -1 && WIFEXITED(status) && WEXITSTATUS(status) == 0;

  if (callback_)
    success = callback_(dump_path_c_, next_minidump_id_c_,
                        callback_context_, success);

  return success;
}

// This function runs in a compromised context: see the top of the file.
void ExceptionHandler::SendContinueSignalToChild() {
  static const char okToContinueMessage = 'a';
  int r;
  r = HANDLE_EINTR(sys_write(fdes[1], &okToContinueMessage, sizeof(char)));
  if(r == -1) {
    static const char msg[] = "ExceptionHandler::SendContinueSignalToChild \
                               sys_write failed:";
    logger::write(msg, sizeof(msg) - 1);
    logger::write(strerror(errno), strlen(strerror(errno)));
    logger::write("\n", 1);
  }
}

// This function runs in a compromised context: see the top of the file.
// Runs on the cloned process.
void ExceptionHandler::WaitForContinueSignal() {
  int r;
  char receivedMessage;
  r = HANDLE_EINTR(sys_read(fdes[0], &receivedMessage, sizeof(char)));
  if(r == -1) {
    static const char msg[] = "ExceptionHandler::WaitForContinueSignal \
                               sys_read failed:";
    logger::write(msg, sizeof(msg) - 1);
    logger::write(strerror(errno), strlen(strerror(errno)));
    logger::write("\n", 1);
  }
}

// This function runs in a compromised context: see the top of the file.
// Runs on the cloned process.
bool ExceptionHandler::DoDump(pid_t crashing_process, const void* context,
                              size_t context_size) {
  return google_breakpad::WriteMinidump(next_minidump_path_c_,
                                        crashing_process,
                                        context,
                                        context_size,
                                        mapping_list_);
}

// static
bool ExceptionHandler::WriteMinidump(const std::string &dump_path,
                                     MinidumpCallback callback,
                                     void* callback_context) {
  ExceptionHandler eh(dump_path, NULL, callback, callback_context, false);
  return eh.WriteMinidump();
}

bool ExceptionHandler::WriteMinidump() {
#if !defined(__ARM_EABI__)
  // Allow ourselves to be dumped.
  sys_prctl(PR_SET_DUMPABLE, 1);

  CrashContext context;
  int getcontext_result = getcontext(&context.context);
  if (getcontext_result)
    return false;
  memcpy(&context.float_state, context.context.uc_mcontext.fpregs,
         sizeof(context.float_state));
  context.tid = sys_gettid();

  bool success = GenerateDump(&context);
  UpdateNextID();
  return success;
#else
  return false;
#endif  // !defined(__ARM_EABI__)
}

void ExceptionHandler::AddMappingInfo(const std::string& name,
                                      const u_int8_t identifier[sizeof(MDGUID)],
                                      uintptr_t start_address,
                                      size_t mapping_size,
                                      size_t file_offset) {
  MappingInfo info;
  info.start_addr = start_address;
  info.size = mapping_size;
  info.offset = file_offset;
  strncpy(info.name, name.c_str(), sizeof(info.name) - 1);
  info.name[sizeof(info.name) - 1] = '\0';

  MappingEntry mapping;
  mapping.first = info;
  memcpy(mapping.second, identifier, sizeof(MDGUID));
  mapping_list_.push_back(mapping);
}

}  // namespace google_breakpad