src/bsp/lk/lib/libavb/avb_slot_verify.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_chain_partition_descriptor.h"
#include "avb_cmdline.h"
#include "avb_footer.h"
#include "avb_hash_descriptor.h"
#include "avb_hashtree_descriptor.h"
#include "avb_kernel_cmdline_descriptor.h"
#include "avb_sha.h"
#include "avb_slot_verify.h"
#include "avb_util.h"
#include "avb_vbmeta_image.h"
#include "avb_version.h"

/* Maximum number of partitions that can be loaded with avb_slot_verify(). */
#define MAX_NUMBER_OF_LOADED_PARTITIONS 32

/* Maximum number of vbmeta images that can be loaded with avb_slot_verify(). */
#define MAX_NUMBER_OF_VBMETA_IMAGES 32

/* Maximum size of a vbmeta image - 64 KiB. */
#define VBMETA_MAX_SIZE (64 * 1024)

/* Helper function to see if we should continue with verification in
 * allow_verification_error=true mode if something goes wrong. See the
 * comments for the avb_slot_verify() function for more information.
 */
static inline bool result_should_continue(AvbSlotVerifyResult result)
{
    switch (result) {
        case AVB_SLOT_VERIFY_RESULT_ERROR_OOM:
        case AVB_SLOT_VERIFY_RESULT_ERROR_IO:
        case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA:
        case AVB_SLOT_VERIFY_RESULT_ERROR_UNSUPPORTED_VERSION:
        case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT:
            return false;

        case AVB_SLOT_VERIFY_RESULT_OK:
        case AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION:
        case AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX:
        case AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED:
            return true;
    }

    return false;
}

static AvbSlotVerifyResult load_full_partition(AvbOps *ops,
        const char *part_name,
        uint64_t image_size,
        uint8_t **out_image_buf,
        bool *out_image_preloaded)
{
    size_t part_num_read;
    AvbIOResult io_ret;

    /* Make sure that we do not overwrite existing data. */
    avb_assert(*out_image_buf == NULL);
    avb_assert(!*out_image_preloaded);

    /* We are going to implicitly cast image_size from uint64_t to size_t in the
     * following code, so we need to make sure that the cast is safe. */
    if (image_size != (size_t)(image_size)) {
        avb_errorv(part_name, ": Partition size too large to load.\n", NULL);
        return AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
    }

    /* Try use a preloaded one. */
    if (ops->get_preloaded_partition != NULL) {
        io_ret = ops->get_preloaded_partition(
                     ops, part_name, image_size, out_image_buf, &part_num_read);
        if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
            return AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        } else if (io_ret != AVB_IO_RESULT_OK) {
            avb_errorv(part_name, ": Error loading data from partition.\n", NULL);
            return AVB_SLOT_VERIFY_RESULT_ERROR_IO;
        }

        if (*out_image_buf != NULL) {
            if (part_num_read != image_size) {
                avb_errorv(part_name, ": Read incorrect number of bytes.\n", NULL);
                return AVB_SLOT_VERIFY_RESULT_ERROR_IO;
            }
            *out_image_preloaded = true;
        }
    }

    /* Allocate and copy the partition. */
    if (!*out_image_preloaded) {
        *out_image_buf = avb_malloc(image_size);
        if (*out_image_buf == NULL) {
            return AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        }

        io_ret = ops->read_from_partition(ops,
                                          part_name,
                                          0 /* offset */,
                                          image_size,
                                          *out_image_buf,
                                          &part_num_read);
        if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
            return AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        } else if (io_ret != AVB_IO_RESULT_OK) {
            avb_errorv(part_name, ": Error loading data from partition.\n", NULL);
            return AVB_SLOT_VERIFY_RESULT_ERROR_IO;
        }
        if (part_num_read != image_size) {
            avb_errorv(part_name, ": Read incorrect number of bytes.\n", NULL);
            return AVB_SLOT_VERIFY_RESULT_ERROR_IO;
        }
    }

    return AVB_SLOT_VERIFY_RESULT_OK;
}

static AvbSlotVerifyResult read_persistent_digest(AvbOps *ops,
        const char *part_name,
        size_t expected_digest_size,
        uint8_t *out_digest)
{
    char *persistent_value_name = NULL;
    AvbIOResult io_ret = AVB_IO_RESULT_OK;
    size_t stored_digest_size = 0;

    if (ops->read_persistent_value == NULL) {
        avb_errorv(part_name, ": Persistent values are not implemented.\n", NULL);
        return AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
    }
    persistent_value_name =
        avb_strdupv(AVB_NPV_PERSISTENT_DIGEST_PREFIX, part_name, NULL);
    if (persistent_value_name == NULL) {
        return AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    }
    io_ret = ops->read_persistent_value(ops,
                                        persistent_value_name,
                                        expected_digest_size,
                                        out_digest,
                                        &stored_digest_size);
    avb_free(persistent_value_name);
    if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
        return AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
    } else if (io_ret == AVB_IO_RESULT_ERROR_NO_SUCH_VALUE) {
        avb_errorv(part_name, ": Persistent digest does not exist.\n", NULL);
        return AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
    } else if (io_ret == AVB_IO_RESULT_ERROR_INVALID_VALUE_SIZE ||
               io_ret == AVB_IO_RESULT_ERROR_INSUFFICIENT_SPACE ||
               expected_digest_size != stored_digest_size) {
        avb_errorv(
            part_name, ": Persistent digest is not of expected size.\n", NULL);
        return AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
    } else if (io_ret != AVB_IO_RESULT_OK) {
        avb_errorv(part_name, ": Error reading persistent digest.\n", NULL);
        return AVB_SLOT_VERIFY_RESULT_ERROR_IO;
    }
    return AVB_SLOT_VERIFY_RESULT_OK;
}

static AvbSlotVerifyResult load_and_verify_hash_partition(
    AvbOps *ops,
    const char *const *requested_partitions,
    const char *ab_suffix,
    bool allow_verification_error,
    const AvbDescriptor *descriptor,
    AvbSlotVerifyData *slot_data)
{
    AvbHashDescriptor hash_desc;
    const uint8_t *desc_partition_name = NULL;
    const uint8_t *desc_salt;
    const uint8_t *desc_digest;
    char part_name[AVB_PART_NAME_MAX_SIZE];
    AvbSlotVerifyResult ret;
    AvbIOResult io_ret;
    uint8_t *image_buf = NULL;
    bool image_preloaded = false;
    uint8_t *digest;
    size_t digest_len;
    const char *found;
    uint64_t image_size;
    size_t expected_digest_len = 0;
    uint8_t expected_digest_buf[AVB_SHA512_DIGEST_SIZE];
    const uint8_t *expected_digest = NULL;

    if (!avb_hash_descriptor_validate_and_byteswap(
                (const AvbHashDescriptor *)descriptor, &hash_desc)) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    desc_partition_name =
        ((const uint8_t *)descriptor) + sizeof(AvbHashDescriptor);
    desc_salt = desc_partition_name + hash_desc.partition_name_len;
    desc_digest = desc_salt + hash_desc.salt_len;

    if (!avb_validate_utf8(desc_partition_name, hash_desc.partition_name_len)) {
        avb_error("Partition name is not valid UTF-8.\n");
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    /* Don't bother loading or validating unless the partition was
     * requested in the first place.
     */
    found = avb_strv_find_str(requested_partitions,
                              (const char *)desc_partition_name,
                              hash_desc.partition_name_len);
    if (found == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_OK;
        goto out;
    }

    if ((hash_desc.flags & AVB_HASH_DESCRIPTOR_FLAGS_DO_NOT_USE_AB) != 0) {
        /* No ab_suffix, just copy the partition name as is. */
        if (hash_desc.partition_name_len >= AVB_PART_NAME_MAX_SIZE) {
            avb_error("Partition name does not fit.\n");
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
            goto out;
        }
        avb_memcpy(part_name, desc_partition_name, hash_desc.partition_name_len);
        part_name[hash_desc.partition_name_len] = '\0';
    } else if (hash_desc.digest_len == 0 && avb_strlen(ab_suffix) != 0) {
        /* No ab_suffix allowed for partitions without a digest in the descriptor
         * because these partitions hold data unique to this device and are not
         * updated using an A/B scheme.
         */
        avb_error("Cannot use A/B with a persistent digest.\n");
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    } else {
        /* Add ab_suffix to the partition name. */
        if (!avb_str_concat(part_name,
                            sizeof part_name,
                            (const char *)desc_partition_name,
                            hash_desc.partition_name_len,
                            ab_suffix,
                            avb_strlen(ab_suffix))) {
            avb_error("Partition name and suffix does not fit.\n");
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
            goto out;
        }
    }

    /* If we're allowing verification errors then hash_desc.image_size
     * may no longer match what's in the partition... so in this case
     * just load the entire partition.
     *
     * For example, this can happen if a developer does 'fastboot flash
     * boot /path/to/new/and/bigger/boot.img'. We want this to work
     * since it's such a common workflow.
     */
    image_size = hash_desc.image_size;
    if (allow_verification_error) {
        io_ret = ops->get_size_of_partition(ops, part_name, &image_size);
        if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto out;
        } else if (io_ret != AVB_IO_RESULT_OK) {
            avb_errorv(part_name, ": Error determining partition size.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
            goto out;
        }
       avb_debugv(part_name, ": Loading entire partition.\n", NULL);
    }

    ret = load_full_partition(
              ops, part_name, image_size, &image_buf, &image_preloaded);
    if (ret != AVB_SLOT_VERIFY_RESULT_OK) {
        goto out;
    }

    if (avb_strcmp((const char *)hash_desc.hash_algorithm, "sha256") == 0) {
        AvbSHA256Ctx sha256_ctx;
        avb_sha256_init(&sha256_ctx);
        avb_sha256_update(&sha256_ctx, desc_salt, hash_desc.salt_len);
        avb_sha256_update(&sha256_ctx, image_buf, hash_desc.image_size);
        digest = avb_sha256_final(&sha256_ctx);
        digest_len = AVB_SHA256_DIGEST_SIZE;
    } else if (avb_strcmp((const char *)hash_desc.hash_algorithm, "sha512") == 0) {
        AvbSHA512Ctx sha512_ctx;
        avb_sha512_init(&sha512_ctx);
        avb_sha512_update(&sha512_ctx, desc_salt, hash_desc.salt_len);
        avb_sha512_update(&sha512_ctx, image_buf, hash_desc.image_size);
        digest = avb_sha512_final(&sha512_ctx);
        digest_len = AVB_SHA512_DIGEST_SIZE;
    } else {
        avb_errorv(part_name, ": Unsupported hash algorithm.\n", NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    if (hash_desc.digest_len == 0) {
        // Expect a match to a persistent digest.
        avb_debugv(part_name, ": No digest, using persistent digest.\n", NULL);
        expected_digest_len = digest_len;
        expected_digest = expected_digest_buf;
        avb_assert(expected_digest_len <= sizeof(expected_digest_buf));
        ret =
            read_persistent_digest(ops, part_name, digest_len, expected_digest_buf);
        if (ret != AVB_SLOT_VERIFY_RESULT_OK) {
            goto out;
        }
    } else {
        // Expect a match to the digest in the descriptor.
        expected_digest_len = hash_desc.digest_len;
        expected_digest = desc_digest;
    }

    if (digest_len != expected_digest_len) {
        avb_errorv(
            part_name, ": Digest in descriptor not of expected size.\n", NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    if (avb_safe_memcmp(digest, expected_digest, digest_len) != 0) {
        avb_errorv(part_name,
                   ": Hash of data does not match digest in descriptor.\n",
                   NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION;
        goto out;
    }

    ret = AVB_SLOT_VERIFY_RESULT_OK;

out:

    /* If it worked and something was loaded, copy to slot_data. */
    if ((ret == AVB_SLOT_VERIFY_RESULT_OK || result_should_continue(ret)) &&
            image_buf != NULL) {
        AvbPartitionData *loaded_partition;
        if (slot_data->num_loaded_partitions == MAX_NUMBER_OF_LOADED_PARTITIONS) {
            avb_errorv(part_name, ": Too many loaded partitions.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto fail;
        }
        loaded_partition =
            &slot_data->loaded_partitions[slot_data->num_loaded_partitions++];
        loaded_partition->partition_name = avb_strdup(found);
        loaded_partition->data_size = image_size;
        loaded_partition->data = image_buf;
        loaded_partition->preloaded = image_preloaded;
        image_buf = NULL;
    }

fail:
    if (image_buf != NULL && !image_preloaded) {
        avb_free(image_buf);
    }
    return ret;
}

static AvbSlotVerifyResult load_requested_partitions(
    AvbOps *ops,
    const char *const *requested_partitions,
    const char *ab_suffix,
    AvbSlotVerifyData *slot_data)
{
    AvbSlotVerifyResult ret;
    uint8_t *image_buf = NULL;
    bool image_preloaded = false;
    size_t n;


    for (n = 0; requested_partitions[n] != NULL; n++) {
        char part_name[AVB_PART_NAME_MAX_SIZE];
        AvbIOResult io_ret;
        uint64_t image_size;
        AvbPartitionData *loaded_partition;

        if (!avb_str_concat(part_name,
                            sizeof part_name,
                            requested_partitions[n],
                            avb_strlen(requested_partitions[n]),
                            ab_suffix,
                            avb_strlen(ab_suffix))) {
            avb_error("Partition name and suffix does not fit.\n");
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
            goto out;
        }

        io_ret = ops->get_size_of_partition(ops, part_name, &image_size);
        if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto out;
        } else if (io_ret != AVB_IO_RESULT_OK) {
            avb_errorv(part_name, ": Error determining partition size.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
            goto out;
        }
        avb_debugv(part_name, ": Loading entire partition.\n", NULL);

        ret = load_full_partition(
                  ops, part_name, image_size, &image_buf, &image_preloaded);
        if (ret != AVB_SLOT_VERIFY_RESULT_OK) {
            goto out;
        }

        /* Move to slot_data. */
        if (slot_data->num_loaded_partitions == MAX_NUMBER_OF_LOADED_PARTITIONS) {
            avb_errorv(part_name, ": Too many loaded partitions.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto out;
        }
        loaded_partition =
            &slot_data->loaded_partitions[slot_data->num_loaded_partitions++];
        loaded_partition->partition_name = avb_strdup(requested_partitions[n]);
        if (loaded_partition->partition_name == NULL) {
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto out;
        }
        loaded_partition->data_size = image_size;
        loaded_partition->data = image_buf; /* Transferring the owner. */
        loaded_partition->preloaded = image_preloaded;
        image_buf = NULL;
        image_preloaded = false;
    }

    ret = AVB_SLOT_VERIFY_RESULT_OK;

out:
    /* Free the current buffer if any. */
    if (image_buf != NULL && !image_preloaded) {
        avb_free(image_buf);
    }
    /* Buffers that are already saved in slot_data will be handled by the caller
     * even on failure. */
    return ret;
}

static AvbSlotVerifyResult load_and_verify_vbmeta(
    AvbOps *ops,
    const char *const *requested_partitions,
    const char *ab_suffix,
    bool allow_verification_error,
    AvbVBMetaImageFlags toplevel_vbmeta_flags,
    int rollback_index_location,
    const char *partition_name,
    size_t partition_name_len,
    const uint8_t *expected_public_key,
    size_t expected_public_key_length,
    AvbSlotVerifyData *slot_data,
    AvbAlgorithmType *out_algorithm_type,
    AvbCmdlineSubstList *out_additional_cmdline_subst)
{
    char full_partition_name[AVB_PART_NAME_MAX_SIZE];
    AvbSlotVerifyResult ret;
    AvbIOResult io_ret;
    size_t vbmeta_offset;
    size_t vbmeta_size;
    uint8_t *vbmeta_buf = NULL;
    size_t vbmeta_num_read;
    AvbVBMetaVerifyResult vbmeta_ret;
    const uint8_t *pk_data;
    size_t pk_len;
    AvbVBMetaImageHeader vbmeta_header;
    uint64_t stored_rollback_index;
    const AvbDescriptor **descriptors = NULL;
    size_t num_descriptors;
    size_t n;
    bool is_main_vbmeta;
    bool is_vbmeta_partition;
    AvbVBMetaData *vbmeta_image_data = NULL;

    ret = AVB_SLOT_VERIFY_RESULT_OK;

    avb_assert(slot_data != NULL);

    /* Since we allow top-level vbmeta in 'boot', use
     * rollback_index_location to determine whether we're the main
     * vbmeta struct.
     */
    is_main_vbmeta = (rollback_index_location == 0);
    is_vbmeta_partition = (avb_strcmp(partition_name, "vbmeta") == 0);

    if (!avb_validate_utf8((const uint8_t *)partition_name, partition_name_len)) {
        avb_error("Partition name is not valid UTF-8.\n");
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    /* Construct full partition name e.g. system_a. */
    if (!avb_str_concat(full_partition_name,
                        sizeof full_partition_name,
                        partition_name,
                        partition_name_len,
                        ab_suffix,
                        avb_strlen(ab_suffix))) {
        avb_error("Partition name and suffix does not fit.\n");
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    /* If we're loading from the main vbmeta partition, the vbmeta struct is in
     * the beginning. Otherwise we may have to locate it via a footer... if no
     * footer is found, we look in the beginning to support e.g. vbmeta_<org>
     * partitions holding data for e.g. super partitions (b/80195851 for
     * rationale).
     */
    vbmeta_offset = 0;
    vbmeta_size = VBMETA_MAX_SIZE;
    if (!is_vbmeta_partition) {
        uint8_t footer_buf[AVB_FOOTER_SIZE];
        size_t footer_num_read;
        AvbFooter footer;

        io_ret = ops->read_from_partition(ops,
                                          full_partition_name,
                                          -AVB_FOOTER_SIZE,
                                          AVB_FOOTER_SIZE,
                                          footer_buf,
                                          &footer_num_read);
        if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto out;
        } else if (io_ret != AVB_IO_RESULT_OK) {
            avb_errorv(full_partition_name, ": Error loading footer.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
            goto out;
        }
        avb_assert(footer_num_read == AVB_FOOTER_SIZE);

        if (!avb_footer_validate_and_byteswap((const AvbFooter *)footer_buf,
                                              &footer)) {
            avb_debugv(full_partition_name, ": No footer detected.\n", NULL);
        } else {
            /* Basic footer sanity check since the data is untrusted. */
            if (footer.vbmeta_size > VBMETA_MAX_SIZE) {
                avb_errorv(full_partition_name, ": Invalid vbmeta size in footer.\n", NULL);
            } else {
                vbmeta_offset = footer.vbmeta_offset;
                vbmeta_size = footer.vbmeta_size;
            }
        }
    }
    vbmeta_buf = avb_malloc(vbmeta_size);
    if (vbmeta_buf == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto out;
    }
    if (vbmeta_offset != 0) {
        avb_debugv("Loading vbmeta struct in footer from partition '",
               full_partition_name,
               "'.\n",
               NULL);
    } else {
        avb_debugv("Loading vbmeta struct from partition '",
               full_partition_name,
               "'.\n",
               NULL);
    }

    io_ret = ops->read_from_partition(ops,
                                      full_partition_name,
                                      vbmeta_offset,
                                      vbmeta_size,
                                      vbmeta_buf,
                                      &vbmeta_num_read);
    if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto out;
    } else if (io_ret != AVB_IO_RESULT_OK) {
        /* If we're looking for 'vbmeta' but there is no such partition,
         * go try to get it from the boot partition instead.
         */
        if (is_main_vbmeta && io_ret == AVB_IO_RESULT_ERROR_NO_SUCH_PARTITION &&
                is_vbmeta_partition) {
            avb_debugv(full_partition_name,
                       ": No such partition. Trying 'boot' instead.\n",
                       NULL);
            ret = load_and_verify_vbmeta(ops,
                                         requested_partitions,
                                         ab_suffix,
                                         allow_verification_error,
                                         0 /* toplevel_vbmeta_flags */,
                                         0 /* rollback_index_location */,
                                         BOOT_PART_NAME,
                                         avb_strlen(BOOT_PART_NAME),
                                         NULL /* expected_public_key */,
                                         0 /* expected_public_key_length */,
                                         slot_data,
                                         out_algorithm_type,
                                         out_additional_cmdline_subst);
            goto out;
        } else {
            avb_errorv(full_partition_name, ": Error loading vbmeta data.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
            goto out;
        }
    }
    avb_assert(vbmeta_num_read <= vbmeta_size);

    /* Check if the image is properly signed and get the public key used
     * to sign the image.
     */
    vbmeta_ret =
        avb_vbmeta_image_verify(vbmeta_buf, vbmeta_num_read, &pk_data, &pk_len);
    switch (vbmeta_ret) {
        case AVB_VBMETA_VERIFY_RESULT_OK:
            avb_assert(pk_data != NULL && pk_len > 0);
            break;

        case AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED:
        case AVB_VBMETA_VERIFY_RESULT_HASH_MISMATCH:
        case AVB_VBMETA_VERIFY_RESULT_SIGNATURE_MISMATCH:
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION;
            avb_errorv(full_partition_name,
                       ": Error verifying vbmeta image: ",
                       avb_vbmeta_verify_result_to_string(vbmeta_ret),
                       "\n",
                       NULL);
            if (!allow_verification_error) {
                goto out;
            }
            break;

        case AVB_VBMETA_VERIFY_RESULT_INVALID_VBMETA_HEADER:
            /* No way to continue this case. */
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
            avb_errorv(full_partition_name,
                       ": Error verifying vbmeta image: invalid vbmeta header\n",
                       NULL);
            goto out;

        case AVB_VBMETA_VERIFY_RESULT_UNSUPPORTED_VERSION:
            /* No way to continue this case. */
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_UNSUPPORTED_VERSION;
            avb_errorv(full_partition_name,
                       ": Error verifying vbmeta image: unsupported AVB version\n",
                       NULL);
            goto out;
    }

    /* Byteswap the header. */
    avb_vbmeta_image_header_to_host_byte_order((AvbVBMetaImageHeader *)vbmeta_buf,
            &vbmeta_header);

    /* If we're the toplevel, assign flags so they'll be passed down. */
    if (is_main_vbmeta) {
        toplevel_vbmeta_flags = (AvbVBMetaImageFlags)vbmeta_header.flags;
    } else {
        if (vbmeta_header.flags != 0) {
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
            avb_errorv(full_partition_name,
                       ": chained vbmeta image has non-zero flags\n",
                       NULL);
            goto out;
        }
    }

    /* Check if key used to make signature matches what is expected. */
    if (pk_data != NULL) {
        if (expected_public_key != NULL) {
            avb_assert(!is_main_vbmeta);
            if (expected_public_key_length != pk_len ||
                    avb_safe_memcmp(expected_public_key, pk_data, pk_len) != 0) {
                avb_errorv(full_partition_name,
                           ": Public key used to sign data does not match key in chain "
                           "partition descriptor.\n",
                           NULL);
                ret = AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED;
                if (!allow_verification_error) {
                    goto out;
                }
            }
        } else {
            bool key_is_trusted = false;
            const uint8_t *pk_metadata = NULL;
            size_t pk_metadata_len = 0;

            if (vbmeta_header.public_key_metadata_size > 0) {
                pk_metadata = vbmeta_buf + sizeof(AvbVBMetaImageHeader) +
                              vbmeta_header.authentication_data_block_size +
                              vbmeta_header.public_key_metadata_offset;
                pk_metadata_len = vbmeta_header.public_key_metadata_size;
            }

            avb_assert(is_main_vbmeta);
            io_ret = ops->validate_vbmeta_public_key(
                         ops, pk_data, pk_len, pk_metadata, pk_metadata_len, &key_is_trusted);
            if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
                ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
                goto out;
            } else if (io_ret != AVB_IO_RESULT_OK) {
                avb_errorv(full_partition_name,
                           ": Error while checking public key used to sign data.\n",
                           NULL);
                ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
                goto out;
            }
            if (!key_is_trusted) {
                avb_errorv(full_partition_name,
                           ": Public key used to sign data rejected.\n",
                           NULL);
                ret = AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED;
                if (!allow_verification_error) {
                    goto out;
                }
            }
        }
    }

    /* Check rollback index. */
    io_ret = ops->read_rollback_index(
                 ops, rollback_index_location, &stored_rollback_index);
    if (io_ret == AVB_IO_RESULT_ERROR_OOM) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto out;
    } else if (io_ret != AVB_IO_RESULT_OK) {
        avb_errorv(full_partition_name,
                   ": Error getting rollback index for location.\n",
                   NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_IO;
        goto out;
    }
    if (vbmeta_header.rollback_index < stored_rollback_index) {
        avb_errorv(
            full_partition_name,
            ": Image rollback index is less than the stored rollback index.\n",
            NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX;
        if (!allow_verification_error) {
            goto out;
        }
    }

    /* Copy vbmeta to vbmeta_images before recursing. */
    if (is_main_vbmeta) {
        avb_assert(slot_data->num_vbmeta_images == 0);
    } else {
        avb_assert(slot_data->num_vbmeta_images > 0);
    }
    if (slot_data->num_vbmeta_images == MAX_NUMBER_OF_VBMETA_IMAGES) {
        avb_errorv(full_partition_name, ": Too many vbmeta images.\n", NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto out;
    }
    vbmeta_image_data = &slot_data->vbmeta_images[slot_data->num_vbmeta_images++];
    vbmeta_image_data->partition_name = avb_strdup(partition_name);
    vbmeta_image_data->vbmeta_data = vbmeta_buf;
    /* Note that |vbmeta_buf| is actually |vbmeta_num_read| bytes long
     * and this includes data past the end of the image. Pass the
     * actual size of the vbmeta image. Also, no need to use
     * avb_safe_add() since the header has already been verified.
     */
    vbmeta_image_data->vbmeta_size =
        sizeof(AvbVBMetaImageHeader) +
        vbmeta_header.authentication_data_block_size +
        vbmeta_header.auxiliary_data_block_size;
    vbmeta_image_data->verify_result = vbmeta_ret;

    /* If verification has been disabled by setting a bit in the image,
     * we're done... except that we need to load the entirety of the
     * requested partitions.
     */
    if (vbmeta_header.flags & AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED) {
        AvbSlotVerifyResult sub_ret;
        avb_debugv(
            full_partition_name, ": VERIFICATION_DISABLED bit is set.\n", NULL);
        /* If load_requested_partitions() fail it is always a fatal
         * failure (e.g. ERROR_INVALID_ARGUMENT, ERROR_OOM, etc.) rather
         * than recoverable (e.g. one where result_should_continue()
         * returns true) and we want to convey that error.
         */
        sub_ret = load_requested_partitions(
                      ops, requested_partitions, ab_suffix, slot_data);
        if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
            ret = sub_ret;
        }
        goto out;
    }

    /* Now go through all descriptors and take the appropriate action:
     *
     * - hash descriptor: Load data from partition, calculate hash, and
     *   checks that it matches what's in the hash descriptor.
     *
     * - hashtree descriptor: Do nothing since verification happens
     *   on-the-fly from within the OS. (Unless the descriptor uses a
     *   persistent digest, in which case we need to find it).
     *
     * - chained partition descriptor: Load the footer, load the vbmeta
     *   image, verify vbmeta image (includes rollback checks, hash
     *   checks, bail on chained partitions).
     */
    descriptors =
        avb_descriptor_get_all(vbmeta_buf, vbmeta_num_read, &num_descriptors);
    for (n = 0; n < num_descriptors; n++) {
        AvbDescriptor desc;

        if (!avb_descriptor_validate_and_byteswap(descriptors[n], &desc)) {
            avb_errorv(full_partition_name, ": Descriptor is invalid.\n", NULL);
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
            goto out;
        }

        switch (desc.tag) {
            case AVB_DESCRIPTOR_TAG_HASH: {
                AvbSlotVerifyResult sub_ret;
                sub_ret = load_and_verify_hash_partition(ops,
                          requested_partitions,
                          ab_suffix,
                          allow_verification_error,
                          descriptors[n],
                          slot_data);
                if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
                    ret = sub_ret;
                    if (!allow_verification_error || !result_should_continue(ret)) {
                        goto out;
                    }
                }
            }
            break;

            case AVB_DESCRIPTOR_TAG_CHAIN_PARTITION: {
                AvbSlotVerifyResult sub_ret;
                AvbChainPartitionDescriptor chain_desc;
                const uint8_t *chain_partition_name;
                const uint8_t *chain_public_key;

                /* Only allow CHAIN_PARTITION descriptors in the main vbmeta image. */
                if (!is_main_vbmeta) {
                    avb_errorv(full_partition_name,
                               ": Encountered chain descriptor not in main image.\n",
                               NULL);
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                    goto out;
                }

                if (!avb_chain_partition_descriptor_validate_and_byteswap(
                            (AvbChainPartitionDescriptor *)descriptors[n], &chain_desc)) {
                    avb_errorv(full_partition_name,
                               ": Chain partition descriptor is invalid.\n",
                               NULL);
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                    goto out;
                }

                if (chain_desc.rollback_index_location == 0) {
                    avb_errorv(full_partition_name,
                               ": Chain partition has invalid "
                               "rollback_index_location field.\n",
                               NULL);
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                    goto out;
                }

                chain_partition_name = ((const uint8_t *)descriptors[n]) +
                                       sizeof(AvbChainPartitionDescriptor);
                chain_public_key = chain_partition_name + chain_desc.partition_name_len;

                sub_ret =
                    load_and_verify_vbmeta(ops,
                                           requested_partitions,
                                           ab_suffix,
                                           allow_verification_error,
                                           toplevel_vbmeta_flags,
                                           chain_desc.rollback_index_location,
                                           (const char *)chain_partition_name,
                                           chain_desc.partition_name_len,
                                           chain_public_key,
                                           chain_desc.public_key_len,
                                           slot_data,
                                           NULL, /* out_algorithm_type */
                                           NULL /* out_additional_cmdline_subst */);
                if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
                    ret = sub_ret;
                    if (!result_should_continue(ret)) {
                        goto out;
                    }
                }
            }
            break;

            case AVB_DESCRIPTOR_TAG_KERNEL_CMDLINE: {
                const uint8_t *kernel_cmdline;
                AvbKernelCmdlineDescriptor kernel_cmdline_desc;
                bool apply_cmdline;

                if (!avb_kernel_cmdline_descriptor_validate_and_byteswap(
                            (AvbKernelCmdlineDescriptor *)descriptors[n],
                            &kernel_cmdline_desc)) {
                    avb_errorv(full_partition_name,
                               ": Kernel cmdline descriptor is invalid.\n",
                               NULL);
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                    goto out;
                }

                kernel_cmdline = ((const uint8_t *)descriptors[n]) +
                                 sizeof(AvbKernelCmdlineDescriptor);

                if (!avb_validate_utf8(kernel_cmdline,
                                       kernel_cmdline_desc.kernel_cmdline_length)) {
                    avb_errorv(full_partition_name,
                               ": Kernel cmdline is not valid UTF-8.\n",
                               NULL);
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                    goto out;
                }

                /* Compare the flags for top-level VBMeta struct with flags in
                 * the command-line descriptor so command-line snippets only
                 * intended for a certain mode (dm-verity enabled/disabled)
                 * are skipped if applicable.
                 */
                apply_cmdline = true;
                if (toplevel_vbmeta_flags & AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED) {
                    if (kernel_cmdline_desc.flags &
                            AVB_KERNEL_CMDLINE_FLAGS_USE_ONLY_IF_HASHTREE_NOT_DISABLED) {
                        apply_cmdline = false;
                    }
                } else {
                    if (kernel_cmdline_desc.flags &
                            AVB_KERNEL_CMDLINE_FLAGS_USE_ONLY_IF_HASHTREE_DISABLED) {
                        apply_cmdline = false;
                    }
                }

                if (apply_cmdline) {
                    if (slot_data->cmdline == NULL) {
                        slot_data->cmdline =
                            avb_calloc(kernel_cmdline_desc.kernel_cmdline_length + 1);
                        if (slot_data->cmdline == NULL) {
                            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
                            goto out;
                        }
                        avb_memcpy(slot_data->cmdline,
                                   kernel_cmdline,
                                   kernel_cmdline_desc.kernel_cmdline_length);
                    } else {
                        /* new cmdline is: <existing_cmdline> + ' ' + <newcmdline> + '\0' */
                        size_t orig_size = avb_strlen(slot_data->cmdline);
                        size_t new_size =
                            orig_size + 1 + kernel_cmdline_desc.kernel_cmdline_length + 1;
                        char *new_cmdline = avb_calloc(new_size);
                        if (new_cmdline == NULL) {
                            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
                            goto out;
                        }
                        avb_memcpy(new_cmdline, slot_data->cmdline, orig_size);
                        new_cmdline[orig_size] = ' ';
                        avb_memcpy(new_cmdline + orig_size + 1,
                                   kernel_cmdline,
                                   kernel_cmdline_desc.kernel_cmdline_length);
                        avb_free(slot_data->cmdline);
                        slot_data->cmdline = new_cmdline;
                    }
                }
            }
            break;

            case AVB_DESCRIPTOR_TAG_HASHTREE: {
                AvbHashtreeDescriptor hashtree_desc;

                if (!avb_hashtree_descriptor_validate_and_byteswap(
                            (AvbHashtreeDescriptor *)descriptors[n], &hashtree_desc)) {
                    avb_errorv(
                        full_partition_name, ": Hashtree descriptor is invalid.\n", NULL);
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                    goto out;
                }

                /* We only need to continue when there is no digest in the descriptor.
                 * This is because the only processing here is to find the digest and
                 * make it available on the kernel command line.
                 */
                if (hashtree_desc.root_digest_len == 0) {
                    char part_name[AVB_PART_NAME_MAX_SIZE];
                    size_t digest_len = 0;
                    uint8_t digest_buf[AVB_SHA512_DIGEST_SIZE];
                    const uint8_t *desc_partition_name =
                        ((const uint8_t *)descriptors[n]) + sizeof(AvbHashtreeDescriptor);

                    if (!avb_validate_utf8(desc_partition_name,
                                           hashtree_desc.partition_name_len)) {
                        avb_error("Partition name is not valid UTF-8.\n");
                        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                        goto out;
                    }

                    /* No ab_suffix for partitions without a digest in the descriptor
                     * because these partitions hold data unique to this device and are
                     * not updated using an A/B scheme.
                     */
                    if ((hashtree_desc.flags &
                            AVB_HASHTREE_DESCRIPTOR_FLAGS_DO_NOT_USE_AB) == 0 &&
                            avb_strlen(ab_suffix) != 0) {
                        avb_error("Cannot use A/B with a persistent root digest.\n");
                        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                        goto out;
                    }
                    if (hashtree_desc.partition_name_len >= AVB_PART_NAME_MAX_SIZE) {
                        avb_error("Partition name does not fit.\n");
                        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                        goto out;
                    }
                    avb_memcpy(
                        part_name, desc_partition_name, hashtree_desc.partition_name_len);
                    part_name[hashtree_desc.partition_name_len] = '\0';

                    /* Determine the expected digest size from the hash algorithm. */
                    if (avb_strcmp((const char *)hashtree_desc.hash_algorithm, "sha1") ==
                            0) {
                        digest_len = AVB_SHA1_DIGEST_SIZE;
                    } else if (avb_strcmp((const char *)hashtree_desc.hash_algorithm,
                                          "sha256") == 0) {
                        digest_len = AVB_SHA256_DIGEST_SIZE;
                    } else if (avb_strcmp((const char *)hashtree_desc.hash_algorithm,
                                          "sha512") == 0) {
                        digest_len = AVB_SHA512_DIGEST_SIZE;
                    } else {
                        avb_errorv(part_name, ": Unsupported hash algorithm.\n", NULL);
                        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
                        goto out;
                    }

                    ret = read_persistent_digest(ops, part_name, digest_len, digest_buf);
                    if (ret != AVB_SLOT_VERIFY_RESULT_OK) {
                        goto out;
                    }

                    if (out_additional_cmdline_subst) {
                        ret =
                            avb_add_root_digest_substitution(part_name,
                                                             digest_buf,
                                                             digest_len,
                                                             out_additional_cmdline_subst);
                        if (ret != AVB_SLOT_VERIFY_RESULT_OK) {
                            goto out;
                        }
                    }
                }
            }
            break;

            case AVB_DESCRIPTOR_TAG_PROPERTY:
                /* Do nothing. */
                break;
        }
    }

    if (rollback_index_location >= AVB_MAX_NUMBER_OF_ROLLBACK_INDEX_LOCATIONS) {
        avb_errorv(
            full_partition_name, ": Invalid rollback_index_location.\n", NULL);
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA;
        goto out;
    }

    slot_data->rollback_indexes[rollback_index_location] =
        vbmeta_header.rollback_index;

    if (out_algorithm_type != NULL) {
        *out_algorithm_type = (AvbAlgorithmType)vbmeta_header.algorithm_type;
    }

out:
    /* If |vbmeta_image_data| isn't NULL it means that it adopted
     * |vbmeta_buf| so in that case don't free it here.
     */
    if (vbmeta_image_data == NULL) {
        if (vbmeta_buf != NULL) {
            avb_free(vbmeta_buf);
        }
    }
    if (descriptors != NULL) {
        avb_free(descriptors);
    }
    return ret;
}

static bool has_system_partition(AvbOps* ops, const char* ab_suffix) {
    char part_name[AVB_PART_NAME_MAX_SIZE];
    const char* system_part_name = "system";
    char guid_buf[37];
    AvbIOResult io_ret;

    if (!avb_str_concat(part_name,
                        sizeof part_name,
                        system_part_name,
                        avb_strlen(system_part_name),
                        ab_suffix,
                        avb_strlen(ab_suffix))) {
        avb_error("System partition name and suffix does not fit.\n");
        return false;
    }

    io_ret = ops->get_unique_guid_for_partition(
        ops, part_name, guid_buf, sizeof guid_buf);
    if (io_ret == AVB_IO_RESULT_ERROR_NO_SUCH_PARTITION) {
        avb_debug("No system partition.\n");
        return false;
    } else if (io_ret != AVB_IO_RESULT_OK) {
        avb_error("Error getting unique GUID for system partition.\n");
        return false;
    }

    return true;
}

AvbSlotVerifyResult avb_slot_verify(AvbOps *ops,
                                    const char *const *requested_partitions,
                                    const char *ab_suffix,
                                    AvbSlotVerifyFlags flags,
                                    AvbHashtreeErrorMode hashtree_error_mode,
                                    AvbSlotVerifyData **out_data)
{
    AvbSlotVerifyResult ret;
    AvbSlotVerifyData *slot_data = NULL;
    AvbAlgorithmType algorithm_type = AVB_ALGORITHM_TYPE_NONE;
    bool using_boot_for_vbmeta = false;
    AvbVBMetaImageHeader toplevel_vbmeta;
    bool allow_verification_error =
        (flags & AVB_SLOT_VERIFY_FLAGS_ALLOW_VERIFICATION_ERROR);
    AvbCmdlineSubstList *additional_cmdline_subst = NULL;

    /* Fail early if we're missing the AvbOps needed for slot verification. */
    avb_assert(ops->read_is_device_unlocked != NULL);
    avb_assert(ops->read_from_partition != NULL);
    avb_assert(ops->get_size_of_partition != NULL);
    avb_assert(ops->validate_vbmeta_public_key != NULL);
    avb_assert(ops->read_rollback_index != NULL);
    avb_assert(ops->get_unique_guid_for_partition != NULL);

    if (out_data != NULL) {
        *out_data = NULL;
    }

    /* Allowing dm-verity errors defeats the purpose of verified boot so
     * only allow this if set up to allow verification errors
     * (e.g. typically only UNLOCKED mode).
     */
    if (hashtree_error_mode == AVB_HASHTREE_ERROR_MODE_LOGGING &&
            !allow_verification_error) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT;
        goto fail;
    }

    slot_data = avb_calloc(sizeof(AvbSlotVerifyData));
    if (slot_data == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto fail;
    }
    slot_data->vbmeta_images =
        avb_calloc(sizeof(AvbVBMetaData) * MAX_NUMBER_OF_VBMETA_IMAGES);
    if (slot_data->vbmeta_images == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto fail;
    }
    slot_data->loaded_partitions =
        avb_calloc(sizeof(AvbPartitionData) * MAX_NUMBER_OF_LOADED_PARTITIONS);
    if (slot_data->loaded_partitions == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto fail;
    }

    additional_cmdline_subst = avb_new_cmdline_subst_list();
    if (additional_cmdline_subst == NULL) {
        ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
        goto fail;
    }

    ret = load_and_verify_vbmeta(ops,
                                 requested_partitions,
                                 ab_suffix,
                                 allow_verification_error,
                                 0 /* toplevel_vbmeta_flags */,
                                 0 /* rollback_index_location */,
                                 "vbmeta",
                                 avb_strlen("vbmeta"),
                                 NULL /* expected_public_key */,
                                 0 /* expected_public_key_length */,
                                 slot_data,
                                 &algorithm_type,
                                 additional_cmdline_subst);
    if (!allow_verification_error && ret != AVB_SLOT_VERIFY_RESULT_OK) {
        goto fail;
    }

    /* If things check out, mangle the kernel command-line as needed. */
    if (result_should_continue(ret)) {
        if (avb_strcmp(slot_data->vbmeta_images[0].partition_name, "vbmeta") != 0) {
            avb_assert(
                avb_strcmp(slot_data->vbmeta_images[0].partition_name, BOOT_PART_NAME) == 0);
            using_boot_for_vbmeta = true;
        }

        /* Byteswap top-level vbmeta header since we'll need it below. */
        avb_vbmeta_image_header_to_host_byte_order(
            (const AvbVBMetaImageHeader *)slot_data->vbmeta_images[0].vbmeta_data,
            &toplevel_vbmeta);

        /* Fill in |ab_suffix| field. */
        slot_data->ab_suffix = avb_strdup(ab_suffix);
        if (slot_data->ab_suffix == NULL) {
            ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
            goto fail;
        }

        /* If verification is disabled, we are done ... we specifically
         * don't want to add any androidboot.* options since verification
         * is disabled.
         */
        if (toplevel_vbmeta.flags & AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED) {
            /* Since verification is disabled we didn't process any
             * descriptors and thus there's no cmdline... so set root= such
             * that the system partition is mounted.
             */
            avb_assert(slot_data->cmdline == NULL);
            // Devices with dynamic partitions won't have system partition.
            // Instead, it has a large super partition to accommodate *.img files.
            // See b/119551429 for details.
            if (has_system_partition(ops, ab_suffix)) {
                slot_data->cmdline =
                    avb_strdup("root=PARTUUID=$(ANDROID_SYSTEM_PARTUUID)");
            } else {
                // The |cmdline| field should be a NUL-terminated string.
                slot_data->cmdline = avb_strdup("");
            }
            if (slot_data->cmdline == NULL) {
                ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
                goto fail;
            }
        } else {
            /* Add options - any failure in avb_append_options() is either an
             * I/O or OOM error.
             */
            AvbSlotVerifyResult sub_ret = avb_append_options(ops,
                                          slot_data,
                                          &toplevel_vbmeta,
                                          algorithm_type,
                                          hashtree_error_mode);
            if (sub_ret != AVB_SLOT_VERIFY_RESULT_OK) {
                ret = sub_ret;
                goto fail;
            }
        }

        /* Substitute $(ANDROID_SYSTEM_PARTUUID) and friends. */
        if (slot_data->cmdline != NULL && avb_strlen(slot_data->cmdline) != 0) {
            char *new_cmdline;
            new_cmdline = avb_sub_cmdline(ops,
                                          slot_data->cmdline,
                                          ab_suffix,
                                          using_boot_for_vbmeta,
                                          additional_cmdline_subst);
            if (new_cmdline != slot_data->cmdline) {
                if (new_cmdline == NULL) {
                    ret = AVB_SLOT_VERIFY_RESULT_ERROR_OOM;
                    goto fail;
                }
                avb_free(slot_data->cmdline);
                slot_data->cmdline = new_cmdline;
            }
        }

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

    avb_free_cmdline_subst_list(additional_cmdline_subst);
    additional_cmdline_subst = NULL;

    if (!allow_verification_error) {
        avb_assert(ret == AVB_SLOT_VERIFY_RESULT_OK);
    }

    return ret;

fail:
    if (slot_data != NULL) {
        avb_slot_verify_data_free(slot_data);
    }
    if (additional_cmdline_subst != NULL) {
        avb_free_cmdline_subst_list(additional_cmdline_subst);
    }
    return ret;
}

void avb_slot_verify_data_free(AvbSlotVerifyData *data)
{
    if (data->ab_suffix != NULL) {
        avb_free(data->ab_suffix);
    }
    if (data->cmdline != NULL) {
        avb_free(data->cmdline);
    }
    if (data->vbmeta_images != NULL) {
        size_t n;
        for (n = 0; n < data->num_vbmeta_images; n++) {
            AvbVBMetaData *vbmeta_image = &data->vbmeta_images[n];
            if (vbmeta_image->partition_name != NULL) {
                avb_free(vbmeta_image->partition_name);
            }
            if (vbmeta_image->vbmeta_data != NULL) {
                avb_free(vbmeta_image->vbmeta_data);
            }
        }
        avb_free(data->vbmeta_images);
    }
    if (data->loaded_partitions != NULL) {
        size_t n;
        for (n = 0; n < data->num_loaded_partitions; n++) {
            AvbPartitionData *loaded_partition = &data->loaded_partitions[n];
            if (loaded_partition->partition_name != NULL) {
                avb_free(loaded_partition->partition_name);
            }
            if (loaded_partition->data != NULL && !loaded_partition->preloaded) {
                avb_free(loaded_partition->data);
            }
        }
        avb_free(data->loaded_partitions);
    }
    avb_free(data);
}

const char *avb_slot_verify_result_to_string(AvbSlotVerifyResult result)
{
    const char *ret = NULL;

    switch (result) {
        case AVB_SLOT_VERIFY_RESULT_OK:
            ret = "OK";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_OOM:
            ret = "ERROR_OOM";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_IO:
            ret = "ERROR_IO";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_VERIFICATION:
            ret = "ERROR_VERIFICATION";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_ROLLBACK_INDEX:
            ret = "ERROR_ROLLBACK_INDEX";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_PUBLIC_KEY_REJECTED:
            ret = "ERROR_PUBLIC_KEY_REJECTED";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_METADATA:
            ret = "ERROR_INVALID_METADATA";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_UNSUPPORTED_VERSION:
            ret = "ERROR_UNSUPPORTED_VERSION";
            break;
        case AVB_SLOT_VERIFY_RESULT_ERROR_INVALID_ARGUMENT:
            ret = "ERROR_INVALID_ARGUMENT";
            break;
            /* Do not add a 'default:' case here because of -Wswitch. */
    }

    if (ret == NULL) {
        avb_error("Unknown AvbSlotVerifyResult value.\n");
        ret = "(unknown)";
    }

    return ret;
}