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/*
* Copyright (C) 2019 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.
*/
#define LOG_TAG "apexd"
#include "apexd_verity.h"
#include <filesystem>
#include <vector>
#include <android-base/file.h>
#include <android-base/result.h>
#include <android-base/unique_fd.h>
#include <verity/hash_tree_builder.h>
#include "apex_constants.h"
#include "apex_file.h"
#include "apexd_utils.h"
using android::base::ErrnoError;
using android::base::Error;
using android::base::ReadFully;
using android::base::Result;
using android::base::unique_fd;
namespace android {
namespace apex {
namespace {
uint8_t HexToBin(char h) {
if (h >= 'A' && h <= 'H') return h - 'A' + 10;
if (h >= 'a' && h <= 'h') return h - 'a' + 10;
return h - '0';
}
std::vector<uint8_t> HexToBin(const std::string& hex) {
std::vector<uint8_t> bin;
bin.reserve(hex.size() / 2);
for (size_t i = 0; i + 1 < hex.size(); i += 2) {
uint8_t c = (HexToBin(hex[i]) << 4) + HexToBin(hex[i + 1]);
bin.push_back(c);
}
return bin;
}
Result<void> GenerateHashTree(const ApexFile& apex,
const ApexVerityData& verity_data,
const std::string& hashtree_file) {
unique_fd fd(TEMP_FAILURE_RETRY(open(apex.GetPath().c_str(), O_RDONLY)));
if (fd.get() == -1) {
return ErrnoError() << "Failed to open " << apex.GetPath();
}
auto block_size = verity_data.desc->hash_block_size;
auto image_size = verity_data.desc->image_size;
auto hash_fn = HashTreeBuilder::HashFunction(verity_data.hash_algorithm);
if (hash_fn == nullptr) {
return Error() << "Unsupported hash algorithm "
<< verity_data.hash_algorithm;
}
auto builder = std::make_unique<HashTreeBuilder>(block_size, hash_fn);
if (!builder->Initialize(image_size, HexToBin(verity_data.salt))) {
return Error() << "Invalid image size " << image_size;
}
if (lseek(fd, apex.GetImageOffset(), SEEK_SET) == -1) {
return ErrnoError() << "Failed to seek";
}
auto block_count = image_size / block_size;
auto buf = std::vector<uint8_t>(block_size);
while (block_count-- > 0) {
if (!ReadFully(fd, buf.data(), block_size)) {
return Error() << "Failed to read";
}
if (!builder->Update(buf.data(), block_size)) {
return Error() << "Failed to build hashtree: Update";
}
}
if (!builder->BuildHashTree()) {
return Error() << "Failed to build hashtree: incomplete data";
}
auto golden_digest = HexToBin(verity_data.root_digest);
auto digest = builder->root_hash();
// This returns zero-padded digest.
// resize() it to compare with golden digest,
digest.resize(golden_digest.size());
if (digest != golden_digest) {
return Error() << "Failed to build hashtree: root digest mismatch";
}
unique_fd out_fd(TEMP_FAILURE_RETRY(
open(hashtree_file.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0600)));
if (!builder->WriteHashTreeToFd(out_fd, 0)) {
return Error() << "Failed to write hashtree to " << hashtree_file;
}
return {};
}
Result<std::string> CalculateRootDigest(const std::string& hashtree_file,
const ApexVerityData& verity_data) {
unique_fd fd(TEMP_FAILURE_RETRY(open(hashtree_file.c_str(), O_RDONLY)));
if (fd.get() == -1) {
return ErrnoError() << "Failed to open " << hashtree_file;
}
auto block_size = verity_data.desc->hash_block_size;
auto image_size = verity_data.desc->image_size;
std::vector<uint8_t> root_verity(block_size);
if (!ReadFully(fd.get(), root_verity.data(), block_size)) {
return ErrnoError() << "Failed to read " << block_size << " bytes from "
<< hashtree_file;
}
auto hash_fn = HashTreeBuilder::HashFunction(verity_data.hash_algorithm);
if (hash_fn == nullptr) {
return Error() << "Unsupported hash algorithm "
<< verity_data.hash_algorithm;
}
auto builder = std::make_unique<HashTreeBuilder>(block_size, hash_fn);
if (!builder->Initialize(image_size, HexToBin(verity_data.salt))) {
return Error() << "Invalid image size " << image_size;
}
std::vector<unsigned char> root_digest;
if (!builder->CalculateRootDigest(root_verity, &root_digest)) {
return Error() << "Failed to calculate digest of " << hashtree_file;
}
auto result = HashTreeBuilder::BytesArrayToString(root_digest);
result.resize(verity_data.root_digest.size());
return result;
}
} // namespace
Result<PrepareHashTreeResult> PrepareHashTree(
const ApexFile& apex, const ApexVerityData& verity_data,
const std::string& hashtree_file) {
if (auto st = createDirIfNeeded(kApexHashTreeDir, 0700); !st.ok()) {
return st.error();
}
bool should_regenerate_hashtree = false;
auto exists = PathExists(hashtree_file);
if (!exists.ok()) {
return exists.error();
}
if (*exists) {
auto digest = CalculateRootDigest(hashtree_file, verity_data);
if (!digest.ok()) {
return digest.error();
}
if (*digest != verity_data.root_digest) {
LOG(ERROR) << "Regenerating hashtree! Digest of " << hashtree_file
<< " does not match digest of " << apex.GetPath() << " : "
<< *digest << "\nvs\n"
<< verity_data.root_digest;
should_regenerate_hashtree = true;
}
} else {
should_regenerate_hashtree = true;
}
if (should_regenerate_hashtree) {
if (auto st = GenerateHashTree(apex, verity_data, hashtree_file);
!st.ok()) {
return st.error();
}
LOG(INFO) << "hashtree: generated to " << hashtree_file;
return KRegenerate;
}
LOG(INFO) << "hashtree: reuse " << hashtree_file;
return kReuse;
}
void RemoveObsoleteHashTrees() {
// TODO(b/120058143): on boot complete, remove unused hashtree files
}
} // namespace apex
} // namespace android
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