init/reboot_utils.cpp

/*
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <sys/capability.h>
#include <sys/reboot.h>
#include <sys/syscall.h>
#include <unistd.h>

#include <string>

#include "android-base/file.h"
#include "android-base/logging.h"
#include "android-base/strings.h"
#include "backtrace/Backtrace.h"
#include "cutils/android_reboot.h"

#include "capabilities.h"

namespace android {
namespace init {

static std::string init_fatal_reboot_target = "bootloader";

void SetFatalRebootTarget() {
    std::string cmdline;
    android::base::ReadFileToString("/proc/cmdline", &cmdline);
    cmdline = android::base::Trim(cmdline);

    const char kRebootTargetString[] = "androidboot.init_fatal_reboot_target=";
    auto start_pos = cmdline.find(kRebootTargetString);
    if (start_pos == std::string::npos) {
        return;  // We already default to bootloader if no setting is provided.
    }
    start_pos += sizeof(kRebootTargetString) - 1;

    auto end_pos = cmdline.find(' ', start_pos);
    // if end_pos isn't found, then we've run off the end, but this is okay as this is the last
    // entry, and -1 is a valid size for string::substr();
    auto size = end_pos == std::string::npos ? -1 : end_pos - start_pos;
    init_fatal_reboot_target = cmdline.substr(start_pos, size);
}

bool IsRebootCapable() {
    if (!CAP_IS_SUPPORTED(CAP_SYS_BOOT)) {
        PLOG(WARNING) << "CAP_SYS_BOOT is not supported";
        return true;
    }

    ScopedCaps caps(cap_get_proc());
    if (!caps) {
        PLOG(WARNING) << "cap_get_proc() failed";
        return true;
    }

    cap_flag_value_t value = CAP_SET;
    if (cap_get_flag(caps.get(), CAP_SYS_BOOT, CAP_EFFECTIVE, &value) != 0) {
        PLOG(WARNING) << "cap_get_flag(CAP_SYS_BOOT, EFFECTIVE) failed";
        return true;
    }
    return value == CAP_SET;
}

void __attribute__((noreturn)) RebootSystem(unsigned int cmd, const std::string& rebootTarget) {
    LOG(INFO) << "Reboot ending, jumping to kernel";

    if (!IsRebootCapable()) {
        // On systems where init does not have the capability of rebooting the
        // device, just exit cleanly.
        exit(0);
    }

    switch (cmd) {
        case ANDROID_RB_POWEROFF:
            reboot(RB_POWER_OFF);
            break;

        case ANDROID_RB_RESTART2:
            syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2,
                    LINUX_REBOOT_CMD_RESTART2, rebootTarget.c_str());
            break;

        case ANDROID_RB_THERMOFF:
            reboot(RB_POWER_OFF);
            break;
    }
    // In normal case, reboot should not return.
    PLOG(ERROR) << "reboot call returned";
    abort();
}

void __attribute__((noreturn)) InitFatalReboot() {
    auto pid = fork();

    if (pid == -1) {
        // Couldn't fork, don't even try to backtrace, just reboot.
        RebootSystem(ANDROID_RB_RESTART2, init_fatal_reboot_target);
    } else if (pid == 0) {
        // Fork a child for safety, since we always want to shut down if something goes wrong, but
        // its worth trying to get the backtrace, even in the signal handler, since typically it
        // does work despite not being async-signal-safe.
        sleep(5);
        RebootSystem(ANDROID_RB_RESTART2, init_fatal_reboot_target);
    }

    // In the parent, let's try to get a backtrace then shutdown.
    std::unique_ptr<Backtrace> backtrace(
            Backtrace::Create(BACKTRACE_CURRENT_PROCESS, BACKTRACE_CURRENT_THREAD));
    if (!backtrace->Unwind(0)) {
        LOG(ERROR) << __FUNCTION__ << ": Failed to unwind callstack.";
    }
    for (size_t i = 0; i < backtrace->NumFrames(); i++) {
        LOG(ERROR) << backtrace->FormatFrameData(i);
    }
    RebootSystem(ANDROID_RB_RESTART2, init_fatal_reboot_target);
}

void InstallRebootSignalHandlers() {
    // Instead of panic'ing the kernel as is the default behavior when init crashes,
    // we prefer to reboot to bootloader on development builds, as this will prevent
    // boot looping bad configurations and allow both developers and test farms to easily
    // recover.
    struct sigaction action;
    memset(&action, 0, sizeof(action));
    sigfillset(&action.sa_mask);
    action.sa_handler = [](int signal) {
        // These signal handlers are also caught for processes forked from init, however we do not
        // want them to trigger reboot, so we directly call _exit() for children processes here.
        if (getpid() != 1) {
            _exit(signal);
        }

        // Calling DoReboot() or LOG(FATAL) is not a good option as this is a signal handler.
        // RebootSystem uses syscall() which isn't actually async-signal-safe, but our only option
        // and probably good enough given this is already an error case and only enabled for
        // development builds.
        InitFatalReboot();
    };
    action.sa_flags = SA_RESTART;
    sigaction(SIGABRT, &action, nullptr);
    sigaction(SIGBUS, &action, nullptr);
    sigaction(SIGFPE, &action, nullptr);
    sigaction(SIGILL, &action, nullptr);
    sigaction(SIGSEGV, &action, nullptr);
#if defined(SIGSTKFLT)
    sigaction(SIGSTKFLT, &action, nullptr);
#endif
    sigaction(SIGSYS, &action, nullptr);
    sigaction(SIGTRAP, &action, nullptr);
}

}  // namespace init
}  // namespace android