libavb/avb_ab_flow.c

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use, copy,
 * modify, merge, publish, distribute, sublicense, and/or sell copies
 * of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "avb_ab_flow.h"
#include "avb_util.h"

bool avb_ab_data_verify_and_byteswap(const AvbABData* src, AvbABData* dest) {
  /* Ensure magic is correct. */
  if (avb_safe_memcmp(src->magic, AVB_AB_MAGIC, AVB_AB_MAGIC_LEN) != 0) {
    avb_error("Magic is incorrect.\n");
    return false;
  }

  avb_memcpy(dest, src, sizeof(AvbABData));
  dest->crc32 = avb_be32toh(dest->crc32);

  /* Ensure we don't attempt to access any fields if the major version
   * is not supported.
   */
  if (dest->version_major > AVB_AB_MAJOR_VERSION) {
    avb_error("No support for given major version.\n");
    return false;
  }

  /* Bail if CRC32 doesn't match. */
  if (dest->crc32 !=
      avb_crc32((const uint8_t*)dest, sizeof(AvbABData) - sizeof(uint32_t))) {
    avb_error("CRC32 does not match.\n");
    return false;
  }

  return true;
}

void avb_ab_data_update_crc_and_byteswap(const AvbABData* src,
                                         AvbABData* dest) {
  avb_memcpy(dest, src, sizeof(AvbABData));
  dest->crc32 = avb_htobe32(
      avb_crc32((const uint8_t*)dest, sizeof(AvbABData) - sizeof(uint32_t)));
}

void avb_ab_data_init(AvbABData* data) {
  avb_memset(data, '\0', sizeof(AvbABData));
  avb_memcpy(data->magic, AVB_AB_MAGIC, AVB_AB_MAGIC_LEN);
  data->version_major = AVB_AB_MAJOR_VERSION;
  data->version_minor = AVB_AB_MINOR_VERSION;
  data->slots[0].priority = AVB_AB_MAX_PRIORITY;
  data->slots[0].tries_remaining = AVB_AB_MAX_TRIES_REMAINING;
  data->slots[0].successful_boot = 0;
  data->slots[1].priority = AVB_AB_MAX_PRIORITY - 1;
  data->slots[1].tries_remaining = AVB_AB_MAX_TRIES_REMAINING;
  data->slots[1].successful_boot = 0;
}

/* The AvbABData struct is stored 2048 bytes into the 'misc' partition
 * following the 'struct bootloader_message' field. The struct is
 * compatible with the guidelines in bootable/recovery/bootloader.h -
 * e.g. it is stored in the |slot_suffix| field, starts with a
 * NUL-byte, and is 32 bytes long.
 */
#define AB_METADATA_MISC_PARTITION_OFFSET 2048

bool avb_ab_data_read(AvbOps* ops, AvbABData* data) {
  AvbABData serialized;
  AvbIOResult io_result;
  size_t num_bytes_read;

  io_result =
      ops->read_from_partition(ops, "misc", AB_METADATA_MISC_PARTITION_OFFSET,
                               sizeof(AvbABData), &serialized, &num_bytes_read);
  if (io_result != AVB_IO_RESULT_OK || num_bytes_read != sizeof(AvbABData)) {
    avb_error("Error reading A/B metadata.\n");
    return false;
  }

  if (!avb_ab_data_verify_and_byteswap(&serialized, data)) {
    avb_error(
        "Error validating A/B metadata from disk. "
        "Resetting and writing new A/B metadata to disk.\n");
    avb_ab_data_init(data);
    return avb_ab_data_write(ops, data);
  }

  return true;
}

bool avb_ab_data_write(AvbOps* ops, const AvbABData* data) {
  AvbABData serialized;
  AvbIOResult io_result;

  avb_ab_data_update_crc_and_byteswap(data, &serialized);
  io_result =
      ops->write_to_partition(ops, "misc", AB_METADATA_MISC_PARTITION_OFFSET,
                              sizeof(AvbABData), &serialized);
  if (io_result != AVB_IO_RESULT_OK) {
    avb_error("Error writing A/B metadata.\n");
    return false;
  }
  return true;
}

static bool slot_is_bootable(AvbABSlotData* slot) {
  return slot->priority > 0 &&
         (slot->successful_boot || (slot->tries_remaining > 0));
}

static void slot_set_unbootable(AvbABSlotData* slot) {
  slot->priority = 0;
  slot->tries_remaining = 0;
  slot->successful_boot = 0;
}

/* Ensure all unbootable and/or illegal states are marked as the
 * canonical 'unbootable' state, e.g. priority=0, tries_remaining=0,
 * and successful_boot=0.
 */
static void slot_normalize(AvbABSlotData* slot) {
  if (slot->priority > 0) {
    if (slot->tries_remaining == 0 && !slot->successful_boot) {
      /* We've exhausted all tries -> unbootable. */
      slot_set_unbootable(slot);
    }
    if (slot->tries_remaining > 0 && slot->successful_boot) {
      /* Illegal state - avb_ab_mark_slot_successful() will clear
       * tries_remaining when setting successful_boot.
       */
      slot_set_unbootable(slot);
    }
  } else {
    slot_set_unbootable(slot);
  }
}

static const char* slot_suffixes[2] = {"_a", "_b"};

/* Helper function to metadata - returns false if an I/O error occurs. */
static bool load_metadata(AvbOps* ops, AvbABData* ab_data,
                          AvbABData* ab_data_orig) {
  if (!avb_ab_data_read(ops, ab_data)) {
    avb_error("I/O error while loading A/B metadata.\n");
    return false;
  }
  *ab_data_orig = *ab_data;

  /* Ensure data is normalized, e.g. illegal states will be marked as
   * unbootable and all unbootable states are represented with
   * (priority=0, tries_remaining=0, successful_boot=0).
   */
  slot_normalize(&ab_data->slots[0]);
  slot_normalize(&ab_data->slots[1]);
  return true;
}

/* Writes A/B metadata to disk only if it has changed - returns false
 * if an I/O error occurs.
 */
static bool save_metadata_if_changed(AvbOps* ops, AvbABData* ab_data,
                                     AvbABData* ab_data_orig) {
  if (avb_safe_memcmp(ab_data, ab_data_orig, sizeof(AvbABData)) != 0) {
    avb_debug("Writing A/B metadata to disk.\n");
    if (!avb_ab_data_write(ops, ab_data)) {
      avb_error("Error writing A/B metadata to disk.\n");
      return false;
    }
  }
  return true;
}

AvbABFlowResult avb_ab_flow(AvbOps* ops, AvbSlotVerifyData** out_data) {
  AvbSlotVerifyData* slot_data[2] = {NULL, NULL};
  AvbSlotVerifyData* data = NULL;
  AvbABFlowResult ret;
  AvbABData ab_data, ab_data_orig;
  size_t slot_index_to_boot, n;

  if (!load_metadata(ops, &ab_data, &ab_data_orig)) {
    ret = AVB_AB_FLOW_RESULT_ERROR_IO;
    goto out;
  }

  /* Validate all bootable slots. */
  for (n = 0; n < 2; n++) {
    if (slot_is_bootable(&ab_data.slots[n])) {
      AvbSlotVerifyResult verify_result;
      verify_result = avb_slot_verify(ops, slot_suffixes[n], &slot_data[n]);
      if (verify_result != AVB_SLOT_VERIFY_RESULT_OK) {
        if (verify_result == AVB_AB_FLOW_RESULT_ERROR_OOM) {
          ret = AVB_AB_FLOW_RESULT_ERROR_OOM;
          goto out;
        }
        if (verify_result == AVB_AB_FLOW_RESULT_ERROR_IO) {
          ret = AVB_AB_FLOW_RESULT_ERROR_IO;
          goto out;
        }
        avb_errorv("Error verifying slot ", slot_suffixes[n], " with result ",
                   avb_slot_verify_result_to_string(verify_result),
                   " - setting unbootable.\n", NULL);
        slot_set_unbootable(&ab_data.slots[n]);
      }
    }
  }

  if (slot_is_bootable(&ab_data.slots[0]) &&
      slot_is_bootable(&ab_data.slots[1])) {
    if (ab_data.slots[1].priority > ab_data.slots[0].priority) {
      slot_index_to_boot = 1;
    } else {
      slot_index_to_boot = 0;
    }
  } else if (slot_is_bootable(&ab_data.slots[0])) {
    slot_index_to_boot = 0;
  } else if (slot_is_bootable(&ab_data.slots[1])) {
    slot_index_to_boot = 1;
  } else {
    /* No bootable slots! */
    avb_error("No bootable slots found.\n");
    ret = AVB_AB_FLOW_RESULT_ERROR_NO_BOOTABLE_SLOTS;
    goto out;
  }

  /* Update stored rollback index such that the stored rollback index
   * is the largest value supporting all currently bootable slots. Do
   * this for every rollback index slot.
   */
  for (n = 0; n < AVB_MAX_NUMBER_OF_ROLLBACK_INDEX_SLOTS; n++) {
    uint64_t rollback_index_value = 0;

    if (slot_data[0] != NULL && slot_data[1] != NULL) {
      uint64_t a_rollback_index = slot_data[0]->rollback_indexes[n];
      uint64_t b_rollback_index = slot_data[1]->rollback_indexes[n];
      rollback_index_value =
          (a_rollback_index < b_rollback_index ? a_rollback_index
                                               : b_rollback_index);
    } else if (slot_data[0] != NULL) {
      rollback_index_value = slot_data[0]->rollback_indexes[n];
    } else if (slot_data[1] != NULL) {
      rollback_index_value = slot_data[1]->rollback_indexes[n];
    }

    if (rollback_index_value != 0) {
      uint64_t current_rollback_index_value;
      if (!ops->read_rollback_index(ops, n, &current_rollback_index_value)) {
        avb_error("Error getting rollback index for slot.\n");
        ret = AVB_AB_FLOW_RESULT_ERROR_IO;
        goto out;
      }
      if (current_rollback_index_value != rollback_index_value) {
        if (!ops->write_rollback_index(ops, n, rollback_index_value)) {
          avb_error("Error setting stored rollback index.\n");
          ret = AVB_AB_FLOW_RESULT_ERROR_IO;
          goto out;
        }
      }
    }
  }

  /* Finally, select this slot. */
  avb_assert(slot_data[slot_index_to_boot] != NULL);
  data = slot_data[slot_index_to_boot];
  slot_data[slot_index_to_boot] = NULL;
  ret = AVB_AB_FLOW_RESULT_OK;

  /* ... and decrement tries remaining, if applicable. */
  if (!ab_data.slots[slot_index_to_boot].successful_boot &&
      ab_data.slots[slot_index_to_boot].tries_remaining > 0) {
    ab_data.slots[slot_index_to_boot].tries_remaining -= 1;
  }

out:
  if (!save_metadata_if_changed(ops, &ab_data, &ab_data_orig)) {
    ret = AVB_AB_FLOW_RESULT_ERROR_IO;
    if (data != NULL) {
      avb_slot_verify_data_free(data);
      data = NULL;
    }
  }

  for (n = 0; n < 2; n++) {
    if (slot_data[n] != NULL) {
      avb_slot_verify_data_free(slot_data[n]);
    }
  }

  if (out_data != NULL) {
    *out_data = data;
  } else {
    if (data != NULL) {
      avb_slot_verify_data_free(data);
    }
  }

  return ret;
}

bool avb_ab_mark_slot_active(AvbOps* ops, unsigned int slot_number) {
  AvbABData ab_data, ab_data_orig;
  bool ret = false;
  unsigned int other_slot_number;

  avb_assert(slot_number < 2);

  if (!load_metadata(ops, &ab_data, &ab_data_orig)) {
    goto out;
  }

  /* Make requested slot top priority, unsuccessful, and with max tries. */
  ab_data.slots[slot_number].priority = AVB_AB_MAX_PRIORITY;
  ab_data.slots[slot_number].tries_remaining = AVB_AB_MAX_TRIES_REMAINING;
  ab_data.slots[slot_number].successful_boot = 0;

  /* Ensure other slot doesn't have as high a priority. */
  other_slot_number = 1 - slot_number;
  if (ab_data.slots[other_slot_number].priority == AVB_AB_MAX_PRIORITY) {
    ab_data.slots[other_slot_number].priority = AVB_AB_MAX_PRIORITY - 1;
  }

  ret = true;

out:
  if (!save_metadata_if_changed(ops, &ab_data, &ab_data_orig)) {
    ret = false;
  }
  return ret;
}

bool avb_ab_mark_slot_unbootable(AvbOps* ops, unsigned int slot_number) {
  AvbABData ab_data, ab_data_orig;
  bool ret = false;

  avb_assert(slot_number < 2);

  if (!load_metadata(ops, &ab_data, &ab_data_orig)) {
    goto out;
  }

  slot_set_unbootable(&ab_data.slots[slot_number]);
  ret = true;

out:
  if (!save_metadata_if_changed(ops, &ab_data, &ab_data_orig)) {
    ret = false;
  }
  return ret;
}

bool avb_ab_mark_slot_successful(AvbOps* ops, unsigned int slot_number) {
  AvbABData ab_data, ab_data_orig;
  bool ret = false;

  avb_assert(slot_number < 2);

  if (!load_metadata(ops, &ab_data, &ab_data_orig)) {
    goto out;
  }

  if (!slot_is_bootable(&ab_data.slots[slot_number])) {
    avb_error("Cannot mark unbootable slot as successful.\n");
    goto out;
  }

  ab_data.slots[slot_number].tries_remaining = 0;
  ab_data.slots[slot_number].successful_boot = 1;

  ret = true;

out:
  if (!save_metadata_if_changed(ops, &ab_data, &ab_data_orig)) {
    ret = false;
  }
  return ret;
}