cryptohome/tpm_persistent_state.cc

// Copyright 2017 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Contains implementation for TpmPersistentState class.

#include "cryptohome/tpm_persistent_state.h"

#include <base/files/file_path.h>

#include "cryptohome/cryptolib.h"
#include "cryptohome/platform.h"

using base::FilePath;
using brillo::SecureBlob;

namespace cryptohome {

extern const FilePath kTpmOwnedFile("/mnt/stateful_partition/.tpm_owned");
const FilePath kTpmStatusFile("/mnt/stateful_partition/.tpm_status");
const FilePath kOpenCryptokiPath("/var/lib/opencryptoki");
const FilePath kShallInitializeFile("/home/.shadow/.can_attempt_ownership");

TpmPersistentState::TpmPersistentState(Platform* platform)
    : platform_(platform) {}

bool TpmPersistentState::SetSealedPassword(const SecureBlob& sealed_password) {
  base::AutoLock lock(tpm_status_lock_);

  if (!LoadTpmStatus()) {
    return false;
  }

  tpm_status_.set_flags(TpmStatus::OWNED_BY_THIS_INSTALL |
                        TpmStatus::USES_RANDOM_OWNER |
                        TpmStatus::INSTALL_ATTRIBUTES_NEEDS_OWNER |
                        TpmStatus::ATTESTATION_NEEDS_OWNER);
  tpm_status_.set_owner_password(sealed_password.data(),
                                 sealed_password.size());

  if (!StoreTpmStatus()) {
    tpm_status_.clear_owner_password();
    return false;
  }
  return true;
}

bool TpmPersistentState::SetDefaultPassword() {
  base::AutoLock lock(tpm_status_lock_);

  if (!LoadTpmStatus()) {
    return false;
  }

  tpm_status_.set_flags(TpmStatus::OWNED_BY_THIS_INSTALL |
                        TpmStatus::USES_WELL_KNOWN_OWNER |
                        TpmStatus::INSTALL_ATTRIBUTES_NEEDS_OWNER |
                        TpmStatus::ATTESTATION_NEEDS_OWNER);
  tpm_status_.clear_owner_password();

  return StoreTpmStatus();
}

bool TpmPersistentState::GetSealedPassword(SecureBlob* sealed_password) {
  base::AutoLock lock(tpm_status_lock_);

  if (!LoadTpmStatus()) {
    return false;
  }

  if (!(tpm_status_.flags() & TpmStatus::OWNED_BY_THIS_INSTALL)) {
    return false;
  }
  if ((tpm_status_.flags() & TpmStatus::USES_WELL_KNOWN_OWNER)) {
    sealed_password->clear();
    return true;
  }
  if (!(tpm_status_.flags() & TpmStatus::USES_RANDOM_OWNER) ||
      !tpm_status_.has_owner_password()) {
    return false;
  }

  sealed_password->resize(tpm_status_.owner_password().size());
  tpm_status_.owner_password().copy(sealed_password->char_data(),
                                    tpm_status_.owner_password().size(), 0);
  return true;
}

bool TpmPersistentState::ClearDependency(TpmOwnerDependency dependency) {
  base::AutoLock lock(tpm_status_lock_);

  int32_t flag_to_clear;
  switch (dependency) {
    case TpmOwnerDependency::kInstallAttributes:
      flag_to_clear = TpmStatus::INSTALL_ATTRIBUTES_NEEDS_OWNER;
      break;
    case TpmOwnerDependency::kAttestation:
      flag_to_clear = TpmStatus::ATTESTATION_NEEDS_OWNER;
      break;
    default:
      return false;
  }

  if (!LoadTpmStatus()) {
    return false;
  }
  if (!(tpm_status_.flags() & flag_to_clear)) {
    return true;
  }
  tpm_status_.set_flags(tpm_status_.flags() & ~flag_to_clear);
  return StoreTpmStatus();
}

bool TpmPersistentState::ClearStoredPasswordIfNotNeeded() {
  base::AutoLock lock(tpm_status_lock_);

  if (!LoadTpmStatus()) {
    return false;
  }

  int32_t dependency_flags = TpmStatus::INSTALL_ATTRIBUTES_NEEDS_OWNER |
                             TpmStatus::ATTESTATION_NEEDS_OWNER;
  if (tpm_status_.flags() & dependency_flags) {
    // The password is still needed, do not clear.
    return false;
  }

  if (!tpm_status_.has_owner_password()) {
    return true;
  }
  tpm_status_.clear_owner_password();
  return StoreTpmStatus();
}

bool TpmPersistentState::ClearStatus() {
  base::AutoLock lock(tpm_status_lock_);

  // Ignore errors: just a cleanup - kOpenCryptokiPath is not used.
  platform_->DeleteFileDurable(kOpenCryptokiPath);
  // Ignore errors: we will overwrite the status later.
  platform_->DeleteFileDurable(kTpmStatusFile);
  tpm_status_.Clear();
  tpm_status_.set_flags(TpmStatus::NONE);
  read_tpm_status_ = true;
  return true;
}

bool TpmPersistentState::IsReady() {
  base::AutoLock lock(tpm_status_lock_);
  return IsReadyLocked();
}

bool TpmPersistentState::SetReady(bool is_ready) {
  base::AutoLock lock(tpm_status_lock_);

  if (IsReadyLocked() == is_ready) {
    return true;
  }
  tpm_ready_ = is_ready;
  // Even if creating/deleting the file below fails, set the in-memory
  // flag to the right value for this boot. If is_ready = true, but the file
  // is not there, next boot will quickly go through checks and attempt
  // to create the file again. if is_ready = false, but the file remained
  // there, we either expect to initialize the tpm on this boot, or leave
  // it as-is (in which case we will deduce it is not actually ready on the
  // next boot in the same way we did it this time).
  // In any case, let's keep the in-memory flag up-to-date ven if it can't
  // be saved in persistent storage.
  return is_ready ? platform_->TouchFileDurable(kTpmOwnedFile)
                  : platform_->DeleteFileDurable(kTpmOwnedFile);
}

bool TpmPersistentState::ShallInitialize() const {
  base::AutoLock lock(tpm_status_lock_);
  return ShallInitializeLocked();
}

bool TpmPersistentState::SetShallInitialize(bool shall_initialize) {
  base::AutoLock lock(tpm_status_lock_);

  if (ShallInitializeLocked() == shall_initialize) {
    return true;
  }
  shall_initialize_ = shall_initialize;
  // See SetReady() above for the decision why we set the cached flag
  // first despite possible filesystem errors later.
  return shall_initialize ? platform_->TouchFileDurable(kShallInitializeFile)
                          : platform_->DeleteFileDurable(kShallInitializeFile);
}

bool TpmPersistentState::LoadTpmStatus() {
  if (read_tpm_status_) {
    return true;
  }
  if (!platform_->FileExists(kTpmStatusFile)) {
    tpm_status_.Clear();
    tpm_status_.set_flags(TpmStatus::NONE);
    read_tpm_status_ = true;
    return true;
  }
  brillo::Blob file_data;
  if (!platform_->ReadFile(kTpmStatusFile, &file_data)) {
    return false;
  }
  tpm_status_.Clear();
  if (!tpm_status_.ParseFromArray(file_data.data(), file_data.size())) {
    return false;
  }
  read_tpm_status_ = true;
  return true;
}

bool TpmPersistentState::StoreTpmStatus() {
  if (platform_->FileExists(kTpmStatusFile)) {
    // Shred old status file, not very useful on SSD. :(
    int64_t file_size;
    if (platform_->GetFileSize(kTpmStatusFile, &file_size)) {
      const auto random = CryptoLib::CreateSecureRandomBlob(file_size);
      platform_->WriteSecureBlobToFile(kTpmStatusFile, random);
      platform_->DataSyncFile(kTpmStatusFile);
    }
    platform_->DeleteFile(kTpmStatusFile);
  }

  SecureBlob final_blob(tpm_status_.ByteSizeLong());
  tpm_status_.SerializeWithCachedSizesToArray(
      static_cast<google::protobuf::uint8*>(final_blob.data()));
  return platform_->WriteSecureBlobToFileAtomicDurable(kTpmStatusFile,
                                                       final_blob, 0600);
}

bool TpmPersistentState::IsReadyLocked() {
  tpm_status_lock_.AssertAcquired();

  if (!read_tpm_ready_) {
    tpm_ready_ = platform_->FileExists(kTpmOwnedFile);
    read_tpm_ready_ = true;
  }
  return tpm_ready_;
}

bool TpmPersistentState::ShallInitializeLocked() const {
  tpm_status_lock_.AssertAcquired();

  if (!read_shall_initialize_) {
    shall_initialize_ = platform_->FileExists(kShallInitializeFile);
    read_shall_initialize_ = true;
  }
  return shall_initialize_;
}

}  // namespace cryptohome