update_verifier/update_verifier.cpp

/*
 * Copyright (C) 2015 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.
 */

/*
 * update_verifier verifies the integrity of the partitions after an A/B OTA update. It gets invoked
 * by init, and will only perform the verification if it's the first boot post an A/B OTA update
 * (https://source.android.com/devices/tech/ota/ab/#after_reboot).
 *
 * update_verifier relies on device-mapper-verity (dm-verity) to capture any corruption on the
 * partitions being verified (https://source.android.com/security/verifiedboot). The verification
 * will be skipped, if dm-verity is not enabled on the device.
 *
 * Upon detecting verification failures, the device will be rebooted, although the trigger of the
 * reboot depends on the dm-verity mode.
 *   enforcing mode: dm-verity reboots the device
 *   eio mode: dm-verity fails the read and update_verifier reboots the device
 *   other mode: not supported and update_verifier reboots the device
 *
 * All these reboots prevent the device from booting into a known corrupt state. If the device
 * continuously fails to boot into the new slot, the bootloader should mark the slot as unbootable
 * and trigger a fallback to the old slot.
 *
 * The current slot will be marked as having booted successfully if the verifier reaches the end
 * after the verification.
 */

#include "update_verifier/update_verifier.h"

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include <algorithm>
#include <future>
#include <string>
#include <vector>

#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/parseint.h>
#include <android-base/properties.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <android/hardware/boot/1.0/IBootControl.h>
#include <cutils/android_reboot.h>

#include "otautil/rangeset.h"

using android::sp;
using android::hardware::boot::V1_0::IBootControl;
using android::hardware::boot::V1_0::BoolResult;
using android::hardware::boot::V1_0::CommandResult;

// Find directories in format of "/sys/block/dm-X".
static int dm_name_filter(const dirent* de) {
  if (android::base::StartsWith(de->d_name, "dm-")) {
    return 1;
  }
  return 0;
}

static bool read_blocks(const std::string& partition, const std::string& range_str) {
  if (partition != "system" && partition != "vendor" && partition != "product") {
    LOG(ERROR) << "Invalid partition name \"" << partition << "\"";
    return false;
  }
  // Iterate the content of "/sys/block/dm-X/dm/name". If it matches one of "system", "vendor" or
  // "product", then dm-X is a dm-wrapped device for that target. We will later read all the
  // ("cared") blocks from "/dev/block/dm-X" to ensure the target partition's integrity.
  static constexpr auto DM_PATH_PREFIX = "/sys/block/";
  dirent** namelist;
  int n = scandir(DM_PATH_PREFIX, &namelist, dm_name_filter, alphasort);
  if (n == -1) {
    PLOG(ERROR) << "Failed to scan dir " << DM_PATH_PREFIX;
    return false;
  }
  if (n == 0) {
    LOG(ERROR) << "dm block device not found for " << partition;
    return false;
  }

  static constexpr auto DM_PATH_SUFFIX = "/dm/name";
  static constexpr auto DEV_PATH = "/dev/block/";
  std::string dm_block_device;
  while (n--) {
    std::string path = DM_PATH_PREFIX + std::string(namelist[n]->d_name) + DM_PATH_SUFFIX;
    std::string content;
    if (!android::base::ReadFileToString(path, &content)) {
      PLOG(WARNING) << "Failed to read " << path;
    } else {
      std::string dm_block_name = android::base::Trim(content);
      // AVB is using 'vroot' for the root block device but we're expecting 'system'.
      if (dm_block_name == "vroot") {
        dm_block_name = "system";
      }
      if (dm_block_name == partition) {
        dm_block_device = DEV_PATH + std::string(namelist[n]->d_name);
        while (n--) {
          free(namelist[n]);
        }
        break;
      }
    }
    free(namelist[n]);
  }
  free(namelist);

  if (dm_block_device.empty()) {
    LOG(ERROR) << "Failed to find dm block device for " << partition;
    return false;
  }

  // For block range string, first integer 'count' equals 2 * total number of valid ranges,
  // followed by 'count' number comma separated integers. Every two integers reprensent a
  // block range with the first number included in range but second number not included.
  // For example '4,64536,65343,74149,74150' represents: [64536,65343) and [74149,74150).
  RangeSet ranges = RangeSet::Parse(range_str);
  if (!ranges) {
    LOG(ERROR) << "Error parsing RangeSet string " << range_str;
    return false;
  }

  // RangeSet::Split() splits the ranges into multiple groups with same number of blocks (except for
  // the last group).
  size_t thread_num = std::thread::hardware_concurrency() ?: 4;
  std::vector<RangeSet> groups = ranges.Split(thread_num);

  std::vector<std::future<bool>> threads;
  for (const auto& group : groups) {
    auto thread_func = [&group, &dm_block_device, &partition]() {
      android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(dm_block_device.c_str(), O_RDONLY)));
      if (fd.get() == -1) {
        PLOG(ERROR) << "Error reading " << dm_block_device << " for partition " << partition;
        return false;
      }

      static constexpr size_t kBlockSize = 4096;
      std::vector<uint8_t> buf(1024 * kBlockSize);

      size_t block_count = 0;
      for (const auto& range : group) {
        size_t range_start = range.first;
        size_t range_end = range.second;
        if (lseek64(fd.get(), static_cast<off64_t>(range_start) * kBlockSize, SEEK_SET) == -1) {
          PLOG(ERROR) << "lseek to " << range_start << " failed";
          return false;
        }

        size_t remain = (range_end - range_start) * kBlockSize;
        while (remain > 0) {
          size_t to_read = std::min(remain, 1024 * kBlockSize);
          if (!android::base::ReadFully(fd.get(), buf.data(), to_read)) {
            PLOG(ERROR) << "Failed to read blocks " << range_start << " to " << range_end;
            return false;
          }
          remain -= to_read;
        }
        block_count += (range_end - range_start);
      }
      LOG(INFO) << "Finished reading " << block_count << " blocks on " << dm_block_device;
      return true;
    };

    threads.emplace_back(std::async(std::launch::async, thread_func));
  }

  bool ret = true;
  for (auto& t : threads) {
    ret = t.get() && ret;
  }
  LOG(INFO) << "Finished reading blocks on " << dm_block_device << " with " << thread_num
            << " threads.";
  return ret;
}

// Returns true to indicate a passing verification (or the error should be ignored); Otherwise
// returns false on fatal errors, where we should reject the current boot and trigger a fallback.
// Note that update_verifier should be backward compatible to not reject care_map.txt from old
// releases, which could otherwise fail to boot into the new release. For example, we've changed
// the care_map format between N and O. An O update_verifier would fail to work with N
// care_map.txt. This could be a result of sideloading an O OTA while the device having a pending N
// update.
bool verify_image(const std::string& care_map_name) {
  android::base::unique_fd care_map_fd(TEMP_FAILURE_RETRY(open(care_map_name.c_str(), O_RDONLY)));
  // If the device is flashed before the current boot, it may not have care_map.txt
  // in /data/ota_package. To allow the device to continue booting in this situation,
  // we should print a warning and skip the block verification.
  if (care_map_fd.get() == -1) {
    PLOG(WARNING) << "Failed to open " << care_map_name;
    return true;
  }
  // care_map file has up to six lines, where every two lines make a pair. Within each pair, the
  // first line has the partition name (e.g. "system"), while the second line holds the ranges of
  // all the blocks to verify.
  std::string file_content;
  if (!android::base::ReadFdToString(care_map_fd.get(), &file_content)) {
    LOG(ERROR) << "Error reading care map contents to string.";
    return false;
  }

  std::vector<std::string> lines;
  lines = android::base::Split(android::base::Trim(file_content), "\n");
  if (lines.size() != 2 && lines.size() != 4 && lines.size() != 6) {
    LOG(ERROR) << "Invalid lines in care_map: found " << lines.size()
               << " lines, expecting 2 or 4 or 6 lines.";
    return false;
  }

  for (size_t i = 0; i < lines.size(); i += 2) {
    // We're seeing an N care_map.txt. Skip the verification since it's not compatible with O
    // update_verifier (the last few metadata blocks can't be read via device mapper).
    if (android::base::StartsWith(lines[i], "/dev/block/")) {
      LOG(WARNING) << "Found legacy care_map.txt; skipped.";
      return true;
    }
    if (!read_blocks(lines[i], lines[i+1])) {
      return false;
    }
  }

  return true;
}

static int reboot_device() {
  if (android_reboot(ANDROID_RB_RESTART2, 0, nullptr) == -1) {
    LOG(ERROR) << "Failed to reboot.";
    return -1;
  }
  while (true) pause();
}

int update_verifier(int argc, char** argv) {
  for (int i = 1; i < argc; i++) {
    LOG(INFO) << "Started with arg " << i << ": " << argv[i];
  }

  sp<IBootControl> module = IBootControl::getService();
  if (module == nullptr) {
    LOG(ERROR) << "Error getting bootctrl module.";
    return reboot_device();
  }

  uint32_t current_slot = module->getCurrentSlot();
  BoolResult is_successful = module->isSlotMarkedSuccessful(current_slot);
  LOG(INFO) << "Booting slot " << current_slot << ": isSlotMarkedSuccessful="
            << static_cast<int32_t>(is_successful);

  if (is_successful == BoolResult::FALSE) {
    // The current slot has not booted successfully.

    bool skip_verification = false;
    std::string verity_mode = android::base::GetProperty("ro.boot.veritymode", "");
    if (verity_mode.empty()) {
      // Skip the verification if ro.boot.veritymode property is not set. This could be a result
      // that device doesn't support dm-verity, or has disabled that.
      LOG(WARNING) << "dm-verity not enabled; marking without verification.";
      skip_verification = true;
    } else if (android::base::EqualsIgnoreCase(verity_mode, "eio")) {
      // We shouldn't see verity in EIO mode if the current slot hasn't booted successfully before.
      // Continue the verification until we fail to read some blocks.
      LOG(WARNING) << "Found dm-verity in EIO mode.";
    } else if (android::base::EqualsIgnoreCase(verity_mode, "disabled")) {
      LOG(WARNING) << "dm-verity in disabled mode; marking without verification.";
      skip_verification = true;
    } else if (verity_mode != "enforcing") {
      LOG(ERROR) << "Unexpected dm-verity mode: " << verity_mode << ", expecting enforcing.";
      return reboot_device();
    }

    if (!skip_verification) {
      static constexpr auto CARE_MAP_FILE = "/data/ota_package/care_map.txt";
      if (!verify_image(CARE_MAP_FILE)) {
        LOG(ERROR) << "Failed to verify all blocks in care map file.";
        return reboot_device();
      }
    }

    CommandResult cr;
    module->markBootSuccessful([&cr](CommandResult result) { cr = result; });
    if (!cr.success) {
      LOG(ERROR) << "Error marking booted successfully: " << cr.errMsg;
      return reboot_device();
    }
    LOG(INFO) << "Marked slot " << current_slot << " as booted successfully.";
  }

  LOG(INFO) << "Leaving update_verifier.";
  return 0;
}