linker/debugger.cpp

/*
 * Copyright (C) 2008 The Android Open Source Project
 * 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.
 *
 * 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.
 */

#include "linker.h"

#include <errno.h>
#include <inttypes.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

extern "C" int tgkill(int tgid, int tid, int sig);

#if __LP64__
#define DEBUGGER_SOCKET_NAME "android:debuggerd64"
#else
#define DEBUGGER_SOCKET_NAME "android:debuggerd"
#endif

enum debugger_action_t {
  // dump a crash
  DEBUGGER_ACTION_CRASH,
  // dump a tombstone file
  DEBUGGER_ACTION_DUMP_TOMBSTONE,
  // dump a backtrace only back to the socket
  DEBUGGER_ACTION_DUMP_BACKTRACE,
};

/* message sent over the socket */
struct debugger_msg_t {
  // version 1 included:
  debugger_action_t action;
  pid_t tid;

  // version 2 added:
  uintptr_t abort_msg_address;

  // version 3 added:
  int32_t original_si_code;
};

// see man(2) prctl, specifically the section about PR_GET_NAME
#define MAX_TASK_NAME_LEN (16)

static int socket_abstract_client(const char* name, int type) {
  sockaddr_un addr;

  // Test with length +1 for the *initial* '\0'.
  size_t namelen = strlen(name);
  if ((namelen + 1) > sizeof(addr.sun_path)) {
    errno = EINVAL;
    return -1;
  }

  // This is used for abstract socket namespace, we need
  // an initial '\0' at the start of the Unix socket path.
  //
  // Note: The path in this case is *not* supposed to be
  // '\0'-terminated. ("man 7 unix" for the gory details.)
  memset(&addr, 0, sizeof(addr));
  addr.sun_family = AF_LOCAL;
  addr.sun_path[0] = 0;
  memcpy(addr.sun_path + 1, name, namelen);

  socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;

  int s = socket(AF_LOCAL, type, 0);
  if (s == -1) {
    return -1;
  }

  int rc = TEMP_FAILURE_RETRY(connect(s, reinterpret_cast<sockaddr*>(&addr), alen));
  if (rc == -1) {
    close(s);
    return -1;
  }

  return s;
}

/*
 * Writes a summary of the signal to the log file.  We do this so that, if
 * for some reason we're not able to contact debuggerd, there is still some
 * indication of the failure in the log.
 *
 * We could be here as a result of native heap corruption, or while a
 * mutex is being held, so we don't want to use any libc functions that
 * could allocate memory or hold a lock.
 */
static void log_signal_summary(int signum, const siginfo_t* info) {
  const char* signal_name = "???";
  bool has_address = false;
  switch (signum) {
    case SIGABRT:
      signal_name = "SIGABRT";
      break;
    case SIGBUS:
      signal_name = "SIGBUS";
      has_address = true;
      break;
    case SIGFPE:
      signal_name = "SIGFPE";
      has_address = true;
      break;
    case SIGILL:
      signal_name = "SIGILL";
      has_address = true;
      break;
    case SIGPIPE:
      signal_name = "SIGPIPE";
      break;
    case SIGSEGV:
      signal_name = "SIGSEGV";
      has_address = true;
      break;
#if defined(SIGSTKFLT)
    case SIGSTKFLT:
      signal_name = "SIGSTKFLT";
      break;
#endif
    case SIGTRAP:
      signal_name = "SIGTRAP";
      break;
  }

  char thread_name[MAX_TASK_NAME_LEN + 1]; // one more for termination
  if (prctl(PR_GET_NAME, (unsigned long)thread_name, 0, 0, 0) != 0) {
    strcpy(thread_name, "<name unknown>");
  } else {
    // short names are null terminated by prctl, but the man page
    // implies that 16 byte names are not.
    thread_name[MAX_TASK_NAME_LEN] = 0;
  }

  // "info" will be null if the siginfo_t information was not available.
  // Many signals don't have an address or a code.
  char code_desc[32]; // ", code -6"
  char addr_desc[32]; // ", fault addr 0x1234"
  addr_desc[0] = code_desc[0] = 0;
  if (info != nullptr) {
    // For a rethrown signal, this si_code will be right and the one debuggerd shows will
    // always be SI_TKILL.
    __libc_format_buffer(code_desc, sizeof(code_desc), ", code %d", info->si_code);
    if (has_address) {
      __libc_format_buffer(addr_desc, sizeof(addr_desc), ", fault addr %p", info->si_addr);
    }
  }
  __libc_format_log(ANDROID_LOG_FATAL, "libc",
                    "Fatal signal %d (%s)%s%s in tid %d (%s)",
                    signum, signal_name, code_desc, addr_desc, gettid(), thread_name);
}

/*
 * Returns true if the handler for signal "signum" has SA_SIGINFO set.
 */
static bool have_siginfo(int signum) {
  struct sigaction old_action, new_action;

  memset(&new_action, 0, sizeof(new_action));
  new_action.sa_handler = SIG_DFL;
  new_action.sa_flags = SA_RESTART;
  sigemptyset(&new_action.sa_mask);

  if (sigaction(signum, &new_action, &old_action) < 0) {
    __libc_format_log(ANDROID_LOG_WARN, "libc", "Failed testing for SA_SIGINFO: %s",
                      strerror(errno));
    return false;
  }
  bool result = (old_action.sa_flags & SA_SIGINFO) != 0;

  if (sigaction(signum, &old_action, nullptr) == -1) {
    __libc_format_log(ANDROID_LOG_WARN, "libc", "Restore failed in test for SA_SIGINFO: %s",
                      strerror(errno));
  }
  return result;
}

static void send_debuggerd_packet(siginfo_t* info) {
  if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 0) {
    // process has disabled core dumps and PTRACE_ATTACH, and does not want to be dumped.
    // Honor that intention by not connecting to debuggerd and asking it
    // to dump our internal state.
    __libc_format_log(ANDROID_LOG_INFO, "libc",
                      "Suppressing debuggerd output because prctl(PR_GET_DUMPABLE)==0");
    return;
  }

  int s = socket_abstract_client(DEBUGGER_SOCKET_NAME, SOCK_STREAM);
  if (s == -1) {
    __libc_format_log(ANDROID_LOG_FATAL, "libc", "Unable to open connection to debuggerd: %s",
                      strerror(errno));
    return;
  }

  // debuggerd knows our pid from the credentials on the
  // local socket but we need to tell it the tid of the crashing thread.
  // debuggerd will be paranoid and verify that we sent a tid
  // that's actually in our process.
  debugger_msg_t msg;
  msg.action = DEBUGGER_ACTION_CRASH;
  msg.tid = gettid();
  msg.abort_msg_address = reinterpret_cast<uintptr_t>(g_abort_message);
  msg.original_si_code = (info != nullptr) ? info->si_code : 0;
  int ret = TEMP_FAILURE_RETRY(write(s, &msg, sizeof(msg)));
  if (ret == sizeof(msg)) {
    char debuggerd_ack;
    ret = TEMP_FAILURE_RETRY(read(s, &debuggerd_ack, 1));
    int saved_errno = errno;
    notify_gdb_of_libraries();
    errno = saved_errno;
  } else {
    // read or write failed -- broken connection?
    __libc_format_log(ANDROID_LOG_FATAL, "libc", "Failed while talking to debuggerd: %s",
                      strerror(errno));
  }

  close(s);
}

/*
 * Catches fatal signals so we can ask debuggerd to ptrace us before
 * we crash.
 */
static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*) {
  // It's possible somebody cleared the SA_SIGINFO flag, which would mean
  // our "info" arg holds an undefined value.
  if (!have_siginfo(signal_number)) {
    info = nullptr;
  }

  log_signal_summary(signal_number, info);

  send_debuggerd_packet(info);

  // Remove our net so we fault for real when we return.
  signal(signal_number, SIG_DFL);

  // These signals are not re-thrown when we resume.  This means that
  // crashing due to (say) SIGPIPE doesn't work the way you'd expect it
  // to.  We work around this by throwing them manually.  We don't want
  // to do this for *all* signals because it'll screw up the si_addr for
  // faults like SIGSEGV. It does screw up the si_code, which is why we
  // passed that to debuggerd above.
  switch (signal_number) {
    case SIGABRT:
    case SIGFPE:
    case SIGPIPE:
#if defined(SIGSTKFLT)
    case SIGSTKFLT:
#endif
    case SIGTRAP:
      tgkill(getpid(), gettid(), signal_number);
      break;
    default:    // SIGILL, SIGBUS, SIGSEGV
      break;
  }
}

__LIBC_HIDDEN__ void debuggerd_init() {
  struct sigaction action;
  memset(&action, 0, sizeof(action));
  sigemptyset(&action.sa_mask);
  action.sa_sigaction = debuggerd_signal_handler;
  action.sa_flags = SA_RESTART | SA_SIGINFO;

  // Use the alternate signal stack if available so we can catch stack overflows.
  action.sa_flags |= SA_ONSTACK;

  sigaction(SIGABRT, &action, nullptr);
  sigaction(SIGBUS, &action, nullptr);
  sigaction(SIGFPE, &action, nullptr);
  sigaction(SIGILL, &action, nullptr);
  sigaction(SIGPIPE, &action, nullptr);
  sigaction(SIGSEGV, &action, nullptr);
#if defined(SIGSTKFLT)
  sigaction(SIGSTKFLT, &action, nullptr);
#endif
  sigaction(SIGTRAP, &action, nullptr);
}