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/*
* Copyright (C) 2020 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 "avb_utils.h"
#include <android-base/strings.h>
#include <libavb/libavb.h>
#include "fec_private.h"
int parse_vbmeta_from_footer(fec_handle *f, std::vector<uint8_t> *vbmeta) {
if (f->size <= AVB_FOOTER_SIZE) {
debug("file size not large enough to be avb images:" PRIu64, f->size);
return -1;
}
AvbFooter footer_read;
if (!raw_pread(f->fd, &footer_read, AVB_FOOTER_SIZE,
f->size - AVB_FOOTER_SIZE)) {
error("failed to read footer: %s", strerror(errno));
return -1;
}
AvbFooter footer;
if (!avb_footer_validate_and_byteswap(&footer_read, &footer)) {
debug("invalid avb footer");
return -1;
}
uint64_t vbmeta_offset = footer.vbmeta_offset;
uint64_t vbmeta_size = footer.vbmeta_size;
check(vbmeta_offset <= f->size - sizeof(footer) - vbmeta_size);
std::vector<uint8_t> vbmeta_data(vbmeta_size, 0);
// TODO(xunchang) handle the sparse image with libsparse.
if (!raw_pread(f->fd, vbmeta_data.data(), vbmeta_data.size(),
vbmeta_offset)) {
error("failed to read avb vbmeta: %s", strerror(errno));
return -1;
}
if (auto status = avb_vbmeta_image_verify(
vbmeta_data.data(), vbmeta_data.size(), nullptr, nullptr);
status != AVB_VBMETA_VERIFY_RESULT_OK &&
status != AVB_VBMETA_VERIFY_RESULT_OK_NOT_SIGNED) {
error("failed to verify avb vbmeta, status: %d", status);
return -1;
}
*vbmeta = std::move(vbmeta_data);
return 0;
}
int parse_avb_image(fec_handle *f, const std::vector<uint8_t> &vbmeta) {
// TODO(xunchang) check if avb verification or hashtree is disabled.
// Look for the hashtree descriptor, we expect exactly one descriptor in
// vbmeta.
// TODO(xunchang) handle the image with AvbHashDescriptor.
auto parse_descriptor = [](const AvbDescriptor *descriptor,
void *user_data) {
if (descriptor &&
avb_be64toh(descriptor->tag) == AVB_DESCRIPTOR_TAG_HASHTREE) {
auto desp = static_cast<const AvbDescriptor **>(user_data);
*desp = descriptor;
return false;
}
return true;
};
const AvbHashtreeDescriptor *hashtree_descriptor_ptr = nullptr;
avb_descriptor_foreach(vbmeta.data(), vbmeta.size(), parse_descriptor,
&hashtree_descriptor_ptr);
if (!hashtree_descriptor_ptr) {
error("failed to find avb hashtree descriptor");
return -1;
}
AvbHashtreeDescriptor hashtree_descriptor;
if (!avb_hashtree_descriptor_validate_and_byteswap(hashtree_descriptor_ptr,
&hashtree_descriptor)) {
error("failed to verify avb hashtree descriptor");
return -1;
}
// The partition name, salt, root append right after the hashtree
// descriptor.
auto read_ptr = reinterpret_cast<const uint8_t *>(hashtree_descriptor_ptr);
// Calculate the offset with respect to the vbmeta; and check both the
// salt & root are within the range.
uint32_t salt_offset =
sizeof(AvbHashtreeDescriptor) + hashtree_descriptor.partition_name_len;
uint32_t root_offset = salt_offset + hashtree_descriptor.salt_len;
check(hashtree_descriptor.salt_len < vbmeta.size());
check(salt_offset < vbmeta.size() - hashtree_descriptor.salt_len);
check(hashtree_descriptor.root_digest_len < vbmeta.size());
check(root_offset < vbmeta.size() - hashtree_descriptor.root_digest_len);
std::vector<uint8_t> salt(
read_ptr + salt_offset,
read_ptr + salt_offset + hashtree_descriptor.salt_len);
std::vector<uint8_t> root_hash(
read_ptr + root_offset,
read_ptr + root_offset + hashtree_descriptor.root_digest_len);
// Expect the AVB image has the format:
// 1. hashtree
// 2. ecc data
// 3. vbmeta
// 4. avb footer
check(hashtree_descriptor.fec_offset ==
hashtree_descriptor.tree_offset + hashtree_descriptor.tree_size);
check(hashtree_descriptor.fec_offset <=
f->size - hashtree_descriptor.fec_size);
f->data_size = hashtree_descriptor.fec_offset;
f->ecc.blocks = fec_div_round_up(f->data_size, FEC_BLOCKSIZE);
f->ecc.rounds = fec_div_round_up(f->ecc.blocks, f->ecc.rsn);
f->ecc.size = hashtree_descriptor.fec_size;
f->ecc.start = hashtree_descriptor.fec_offset;
// TODO(xunchang) verify the integrity of the ecc data.
f->ecc.valid = true;
std::string hash_algorithm =
reinterpret_cast<char *>(hashtree_descriptor.hash_algorithm);
int nid = -1;
if (android::base::EqualsIgnoreCase(hash_algorithm, "sha1")) {
nid = NID_sha1;
} else if (android::base::EqualsIgnoreCase(hash_algorithm, "sha256")) {
nid = NID_sha256;
} else {
error("unsupported hash algorithm %s", hash_algorithm.c_str());
}
hashtree_info hashtree;
hashtree.initialize(hashtree_descriptor.tree_offset,
hashtree_descriptor.tree_offset / FEC_BLOCKSIZE, salt,
nid);
if (hashtree.verify_tree(f, root_hash.data()) != 0) {
error("failed to verify hashtree");
return -1;
}
// We have validate the hashtree,
f->data_size = hashtree.hash_start;
f->avb = {
.valid = true,
.vbmeta = vbmeta,
.hashtree = std::move(hashtree),
};
return 0;
}
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