// Copyright 2018 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. // PLEASE READ BEFORE CHANGING THIS FILE! // // This file implements the support code for the out of bounds signal handler. // Nothing in here actually runs in the signal handler, but the code here // manipulates data structures used by the signal handler so we still need to be // careful. In order to minimize this risk, here are some rules to follow. // // 1. Avoid introducing new external dependencies. The files in src/trap-handler // should be as self-contained as possible to make it easy to audit the code. // // 2. Any changes must be reviewed by someone from the crash reporting // or security team. Se OWNERS for suggested reviewers. // // For more information, see https://goo.gl/yMeyUY. // // For the code that runs in the signal handler itself, see handler-inside.cc. #include <signal.h> #include "src/trap-handler/handler-inside-posix.h" #include "src/trap-handler/trap-handler-internal.h" namespace v8 { namespace internal { namespace trap_handler { #if V8_TRAP_HANDLER_SUPPORTED namespace { struct sigaction g_old_handler; // When using the default signal handler, we save the old one to restore in case // V8 chooses not to handle the signal. bool g_is_default_signal_handler_registered; } // namespace bool RegisterDefaultTrapHandler() { CHECK(!g_is_default_signal_handler_registered); struct sigaction action; action.sa_sigaction = HandleSignal; action.sa_flags = SA_SIGINFO; sigemptyset(&action.sa_mask); // {sigaction} installs a new custom segfault handler. On success, it returns // 0. If we get a nonzero value, we report an error to the caller by returning // false. if (sigaction(kOobSignal, &action, &g_old_handler) != 0) { return false; } // Sanitizers often prevent us from installing our own signal handler. Attempt // to detect this and if so, refuse to enable trap handling. // // TODO(chromium:830894): Remove this once all bots support custom signal // handlers. #if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \ defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER) || \ defined(UNDEFINED_SANITIZER) struct sigaction installed_handler; CHECK_EQ(sigaction(kOobSignal, NULL, &installed_handler), 0); // If the installed handler does not point to HandleSignal, then // allow_user_segv_handler is 0. if (installed_handler.sa_sigaction != HandleSignal) { printf( "WARNING: sanitizers are preventing signal handler installation. " "Trap handlers are disabled.\n"); return false; } #endif g_is_default_signal_handler_registered = true; return true; } void RemoveTrapHandler() { if (g_is_default_signal_handler_registered) { if (sigaction(kOobSignal, &g_old_handler, nullptr) == 0) { g_is_default_signal_handler_registered = false; } } } #endif // V8_TRAP_HANDLER_SUPPORTED } // namespace trap_handler } // namespace internal } // namespace v8