payload_consumer/verity_writer_android.cc

//
// Copyright (C) 2018 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 "update_engine/payload_consumer/verity_writer_android.h"

#include <fcntl.h>

#include <algorithm>
#include <memory>

#include <base/logging.h>
#include <base/posix/eintr_wrapper.h>
#include <fec/ecc.h>
extern "C" {
#include <fec.h>
}

#include "update_engine/common/utils.h"

namespace chromeos_update_engine {

namespace verity_writer {
std::unique_ptr<VerityWriterInterface> CreateVerityWriter() {
  return std::make_unique<VerityWriterAndroid>();
}
}  // namespace verity_writer

bool VerityWriterAndroid::Init(const InstallPlan::Partition& partition) {
  partition_ = &partition;

  if (partition_->hash_tree_size != 0 || partition_->fec_size != 0) {
    utils::SetBlockDeviceReadOnly(partition_->target_path, false);
  }
  if (partition_->hash_tree_size != 0) {
    auto hash_function =
        HashTreeBuilder::HashFunction(partition_->hash_tree_algorithm);
    if (hash_function == nullptr) {
      LOG(ERROR) << "Verity hash algorithm not supported: "
                 << partition_->hash_tree_algorithm;
      return false;
    }
    hash_tree_builder_ = std::make_unique<HashTreeBuilder>(
        partition_->block_size, hash_function);
    TEST_AND_RETURN_FALSE(hash_tree_builder_->Initialize(
        partition_->hash_tree_data_size, partition_->hash_tree_salt));
    if (hash_tree_builder_->CalculateSize(partition_->hash_tree_data_size) !=
        partition_->hash_tree_size) {
      LOG(ERROR) << "Verity hash tree size does not match, stored: "
                 << partition_->hash_tree_size << ", calculated: "
                 << hash_tree_builder_->CalculateSize(
                        partition_->hash_tree_data_size);
      return false;
    }
  }
  return true;
}

bool VerityWriterAndroid::Update(uint64_t offset,
                                 const uint8_t* buffer,
                                 size_t size) {
  if (partition_->hash_tree_size != 0) {
    uint64_t hash_tree_data_end =
        partition_->hash_tree_data_offset + partition_->hash_tree_data_size;
    uint64_t start_offset = std::max(offset, partition_->hash_tree_data_offset);
    uint64_t end_offset = std::min(offset + size, hash_tree_data_end);
    if (start_offset < end_offset) {
      TEST_AND_RETURN_FALSE(hash_tree_builder_->Update(
          buffer + start_offset - offset, end_offset - start_offset));

      if (end_offset == hash_tree_data_end) {
        // All hash tree data blocks has been hashed, write hash tree to disk.
        int fd = HANDLE_EINTR(open(partition_->target_path.c_str(), O_WRONLY));
        if (fd < 0) {
          PLOG(ERROR) << "Failed to open " << partition_->target_path
                      << " to write hash tree.";
          return false;
        }
        ScopedFdCloser fd_closer(&fd);

        LOG(INFO) << "Writing verity hash tree to " << partition_->target_path;
        TEST_AND_RETURN_FALSE(hash_tree_builder_->BuildHashTree());
        TEST_AND_RETURN_FALSE(hash_tree_builder_->WriteHashTreeToFd(
            fd, partition_->hash_tree_offset));
        hash_tree_builder_.reset();
      }
    }
  }
  if (partition_->fec_size != 0) {
    uint64_t fec_data_end =
        partition_->fec_data_offset + partition_->fec_data_size;
    if (offset < fec_data_end && offset + size >= fec_data_end) {
      LOG(INFO) << "Writing verity FEC to " << partition_->target_path;
      TEST_AND_RETURN_FALSE(EncodeFEC(partition_->target_path,
                                      partition_->fec_data_offset,
                                      partition_->fec_data_size,
                                      partition_->fec_offset,
                                      partition_->fec_size,
                                      partition_->fec_roots,
                                      partition_->block_size,
                                      false /* verify_mode */));
    }
  }
  return true;
}

bool VerityWriterAndroid::EncodeFEC(const std::string& path,
                                    uint64_t data_offset,
                                    uint64_t data_size,
                                    uint64_t fec_offset,
                                    uint64_t fec_size,
                                    uint32_t fec_roots,
                                    uint32_t block_size,
                                    bool verify_mode) {
  TEST_AND_RETURN_FALSE(data_size % block_size == 0);
  TEST_AND_RETURN_FALSE(fec_roots >= 0 && fec_roots < FEC_RSM);
  // This is the N in RS(M, N), which is the number of bytes for each rs block.
  size_t rs_n = FEC_RSM - fec_roots;
  uint64_t rounds = utils::DivRoundUp(data_size / block_size, rs_n);
  TEST_AND_RETURN_FALSE(rounds * fec_roots * block_size == fec_size);

  std::unique_ptr<void, decltype(&free_rs_char)> rs_char(
      init_rs_char(FEC_PARAMS(fec_roots)), &free_rs_char);
  TEST_AND_RETURN_FALSE(rs_char != nullptr);

  int fd = HANDLE_EINTR(open(path.c_str(), verify_mode ? O_RDONLY : O_RDWR));
  if (fd < 0) {
    PLOG(ERROR) << "Failed to open " << path << " to write FEC.";
    return false;
  }
  ScopedFdCloser fd_closer(&fd);

  for (size_t i = 0; i < rounds; i++) {
    // Encodes |block_size| number of rs blocks each round so that we can read
    // one block each time instead of 1 byte to increase random read
    // performance. This uses about 1 MiB memory for 4K block size.
    brillo::Blob rs_blocks(block_size * rs_n);
    for (size_t j = 0; j < rs_n; j++) {
      brillo::Blob buffer(block_size, 0);
      uint64_t offset =
          fec_ecc_interleave(i * rs_n * block_size + j, rs_n, rounds);
      // Don't read past |data_size|, treat them as 0.
      if (offset < data_size) {
        ssize_t bytes_read = 0;
        TEST_AND_RETURN_FALSE(utils::PReadAll(fd,
                                              buffer.data(),
                                              buffer.size(),
                                              data_offset + offset,
                                              &bytes_read));
        TEST_AND_RETURN_FALSE(bytes_read ==
                              static_cast<ssize_t>(buffer.size()));
      }
      for (size_t k = 0; k < buffer.size(); k++) {
        rs_blocks[k * rs_n + j] = buffer[k];
      }
    }
    brillo::Blob fec(block_size * fec_roots);
    for (size_t j = 0; j < block_size; j++) {
      // Encode [j * rs_n : (j + 1) * rs_n) in |rs_blocks| and write |fec_roots|
      // number of parity bytes to |j * fec_roots| in |fec|.
      encode_rs_char(rs_char.get(),
                     rs_blocks.data() + j * rs_n,
                     fec.data() + j * fec_roots);
    }

    if (verify_mode) {
      brillo::Blob fec_read(fec.size());
      ssize_t bytes_read = 0;
      TEST_AND_RETURN_FALSE(utils::PReadAll(
          fd, fec_read.data(), fec_read.size(), fec_offset, &bytes_read));
      TEST_AND_RETURN_FALSE(bytes_read ==
                            static_cast<ssize_t>(fec_read.size()));
      TEST_AND_RETURN_FALSE(fec == fec_read);
    } else {
      TEST_AND_RETURN_FALSE(
          utils::PWriteAll(fd, fec.data(), fec.size(), fec_offset));
    }
    fec_offset += fec.size();
  }

  return true;
}
}  // namespace chromeos_update_engine