Line data    Source code

       1             : // Copyright 2018 the V8 project authors. All rights reserved.
       2             : // Use of this source code is governed by a BSD-style license that can be
       3             : // found in the LICENSE file.
       4             : 
       5             : // PLEASE READ BEFORE CHANGING THIS FILE!
       6             : //
       7             : // This file implements the support code for the out of bounds signal handler.
       8             : // Nothing in here actually runs in the signal handler, but the code here
       9             : // manipulates data structures used by the signal handler so we still need to be
      10             : // careful. In order to minimize this risk, here are some rules to follow.
      11             : //
      12             : // 1. Avoid introducing new external dependencies. The files in src/trap-handler
      13             : //    should be as self-contained as possible to make it easy to audit the code.
      14             : //
      15             : // 2. Any changes must be reviewed by someone from the crash reporting
      16             : //    or security team. Se OWNERS for suggested reviewers.
      17             : //
      18             : // For more information, see https://goo.gl/yMeyUY.
      19             : //
      20             : // For the code that runs in the signal handler itself, see handler-inside.cc.
      21             : 
      22             : #include <signal.h>
      23             : 
      24             : #include "src/trap-handler/handler-inside-posix.h"
      25             : #include "src/trap-handler/trap-handler-internal.h"
      26             : 
      27             : namespace v8 {
      28             : namespace internal {
      29             : namespace trap_handler {
      30             : 
      31             : #if V8_TRAP_HANDLER_SUPPORTED
      32             : namespace {
      33             : struct sigaction g_old_handler;
      34             : 
      35             : // When using the default signal handler, we save the old one to restore in case
      36             : // V8 chooses not to handle the signal.
      37             : bool g_is_default_signal_handler_registered;
      38             : 
      39             : }  // namespace
      40             : 
      41       57107 : bool RegisterDefaultTrapHandler() {
      42       57107 :   CHECK(!g_is_default_signal_handler_registered);
      43             : 
      44             :   struct sigaction action;
      45       57107 :   action.sa_sigaction = HandleSignal;
      46       57107 :   action.sa_flags = SA_SIGINFO;
      47       57107 :   sigemptyset(&action.sa_mask);
      48             :   // {sigaction} installs a new custom segfault handler. On success, it returns
      49             :   // 0. If we get a nonzero value, we report an error to the caller by returning
      50             :   // false.
      51       57107 :   if (sigaction(kOobSignal, &action, &g_old_handler) != 0) {
      52             :     return false;
      53             :   }
      54             : 
      55             : // Sanitizers often prevent us from installing our own signal handler. Attempt
      56             : // to detect this and if so, refuse to enable trap handling.
      57             : //
      58             : // TODO(chromium:830894): Remove this once all bots support custom signal
      59             : // handlers.
      60             : #if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
      61             :     defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER) ||    \
      62             :     defined(UNDEFINED_SANITIZER)
      63             :   struct sigaction installed_handler;
      64             :   CHECK_EQ(sigaction(kOobSignal, NULL, &installed_handler), 0);
      65             :   // If the installed handler does not point to HandleSignal, then
      66             :   // allow_user_segv_handler is 0.
      67             :   if (installed_handler.sa_sigaction != HandleSignal) {
      68             :     printf(
      69             :         "WARNING: sanitizers are preventing signal handler installation. "
      70             :         "Trap handlers are disabled.\n");
      71             :     return false;
      72             :   }
      73             : #endif
      74             : 
      75       57107 :   g_is_default_signal_handler_registered = true;
      76       57107 :   return true;
      77             : }
      78             : 
      79          18 : void RemoveTrapHandler() {
      80          18 :   if (g_is_default_signal_handler_registered) {
      81           7 :     if (sigaction(kOobSignal, &g_old_handler, nullptr) == 0) {
      82           7 :       g_is_default_signal_handler_registered = false;
      83             :     }
      84             :   }
      85          18 : }
      86             : #endif  // V8_TRAP_HANDLER_SUPPORTED
      87             : 
      88             : }  // namespace trap_handler
      89             : }  // namespace internal
      90             : }  // namespace v8