| /* |
| * Copyright (C) 2021 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 <string> |
| |
| #include <android-base/file.h> |
| #include <android-base/logging.h> |
| #include <binder/IServiceManager.h> |
| |
| #include <fcntl.h> |
| #include <sys/stat.h> |
| #include <sys/types.h> |
| |
| #include "CertUtils.h" |
| #include "KeyConstants.h" |
| #include "KeystoreKey.h" |
| |
| using android::defaultServiceManager; |
| using android::IServiceManager; |
| using android::sp; |
| using android::String16; |
| |
| using android::hardware::security::keymint::Algorithm; |
| using android::hardware::security::keymint::Digest; |
| using android::hardware::security::keymint::KeyParameter; |
| using android::hardware::security::keymint::KeyParameterValue; |
| using android::hardware::security::keymint::KeyPurpose; |
| using android::hardware::security::keymint::PaddingMode; |
| using android::hardware::security::keymint::SecurityLevel; |
| using android::hardware::security::keymint::Tag; |
| |
| using android::system::keystore2::CreateOperationResponse; |
| using android::system::keystore2::Domain; |
| using android::system::keystore2::KeyDescriptor; |
| using android::system::keystore2::KeyEntryResponse; |
| |
| using android::base::Error; |
| using android::base::Result; |
| |
| static KeyDescriptor getKeyDescriptor(const android::String16& keyAlias, int64_t keyNspace) { |
| // AIDL parcelable objects don't have constructor |
| static KeyDescriptor descriptor; |
| static std::once_flag flag; |
| std::call_once(flag, [&]() { |
| descriptor.domain = Domain::SELINUX; |
| descriptor.alias = keyAlias; |
| descriptor.nspace = keyNspace; |
| }); |
| |
| return descriptor; |
| } |
| |
| KeystoreKey::KeystoreKey(std::string signedPubKeyPath, const android::String16& keyAlias, |
| int64_t keyNspace, int keyBootLevel) |
| : mDescriptor(getKeyDescriptor(keyAlias, keyNspace)), |
| mHmacKey(keyAlias, keyNspace, keyBootLevel), mSignedPubKeyPath(std::move(signedPubKeyPath)), |
| mKeyBootLevel(keyBootLevel) {} |
| |
| Result<std::vector<uint8_t>> KeystoreKey::createKey() { |
| std::vector<KeyParameter> params; |
| |
| KeyParameter algo; |
| algo.tag = Tag::ALGORITHM; |
| algo.value = KeyParameterValue::make<KeyParameterValue::algorithm>(Algorithm::RSA); |
| params.push_back(algo); |
| |
| KeyParameter key_size; |
| key_size.tag = Tag::KEY_SIZE; |
| key_size.value = KeyParameterValue::make<KeyParameterValue::integer>(kRsaKeySize); |
| params.push_back(key_size); |
| |
| KeyParameter digest; |
| digest.tag = Tag::DIGEST; |
| digest.value = KeyParameterValue::make<KeyParameterValue::digest>(Digest::SHA_2_256); |
| params.push_back(digest); |
| |
| KeyParameter padding; |
| padding.tag = Tag::PADDING; |
| padding.value = |
| KeyParameterValue::make<KeyParameterValue::paddingMode>(PaddingMode::RSA_PKCS1_1_5_SIGN); |
| params.push_back(padding); |
| |
| KeyParameter exponent; |
| exponent.tag = Tag::RSA_PUBLIC_EXPONENT; |
| exponent.value = KeyParameterValue::make<KeyParameterValue::longInteger>(kRsaKeyExponent); |
| params.push_back(exponent); |
| |
| KeyParameter purpose; |
| purpose.tag = Tag::PURPOSE; |
| purpose.value = KeyParameterValue::make<KeyParameterValue::keyPurpose>(KeyPurpose::SIGN); |
| params.push_back(purpose); |
| |
| KeyParameter auth; |
| auth.tag = Tag::NO_AUTH_REQUIRED; |
| auth.value = KeyParameterValue::make<KeyParameterValue::boolValue>(true); |
| params.push_back(auth); |
| |
| KeyParameter boot_level; |
| boot_level.tag = Tag::MAX_BOOT_LEVEL; |
| boot_level.value = KeyParameterValue::make<KeyParameterValue::integer>(mKeyBootLevel); |
| params.push_back(boot_level); |
| |
| KeyMetadata metadata; |
| auto status = mSecurityLevel->generateKey(mDescriptor, {}, params, 0, {}, &metadata); |
| if (!status.isOk()) { |
| return Error() << "Failed to create new key: " << status; |
| } |
| |
| // Extract the public key from the certificate, HMAC it and store the signature |
| auto cert = metadata.certificate; |
| if (!cert) { |
| return Error() << "Key did not have a certificate."; |
| } |
| auto publicKey = extractPublicKeyFromX509(cert.value()); |
| if (!publicKey.ok()) { |
| return publicKey.error(); |
| } |
| std::string publicKeyString = {publicKey->begin(), publicKey->end()}; |
| auto signature = mHmacKey.sign(publicKeyString); |
| if (!signature.ok()) { |
| return Error() << "Failed to sign public key."; |
| } |
| |
| if (!android::base::WriteStringToFile(*signature, mSignedPubKeyPath)) { |
| return Error() << "Can't write public key signature."; |
| } |
| |
| return *publicKey; |
| } |
| |
| bool KeystoreKey::initialize() { |
| sp<IServiceManager> sm = defaultServiceManager(); |
| if (sm == nullptr) { |
| return false; |
| } |
| auto service = sm->getService(String16("android.system.keystore2.IKeystoreService/default")); |
| if (service == nullptr) { |
| return false; |
| } |
| mService = interface_cast<android::system::keystore2::IKeystoreService>(service); |
| if (mService == nullptr) { |
| return false; |
| } |
| |
| auto status = mService->getSecurityLevel(SecurityLevel::TRUSTED_ENVIRONMENT, &mSecurityLevel); |
| if (!status.isOk()) { |
| return false; |
| } |
| |
| // Initialize the HMAC key we use to sign/verify information about this key |
| auto hmacStatus = mHmacKey.initialize(mService, mSecurityLevel); |
| if (!hmacStatus.ok()) { |
| LOG(ERROR) << hmacStatus.error().message(); |
| return false; |
| } |
| |
| auto key = getOrCreateKey(); |
| if (!key.ok()) { |
| // Delete the HMAC, just in case signing failed, and we could recover by recreating it. |
| mHmacKey.deleteKey(); |
| LOG(ERROR) << key.error().message(); |
| return false; |
| } |
| mPublicKey = *key; |
| LOG(INFO) << "Initialized Keystore key."; |
| return true; |
| } |
| |
| Result<std::vector<uint8_t>> KeystoreKey::verifyExistingKey() { |
| // See if we can fetch an existing key |
| KeyEntryResponse keyEntryResponse; |
| LOG(INFO) << "Trying to retrieve existing keystore key..."; |
| auto status = mService->getKeyEntry(mDescriptor, &keyEntryResponse); |
| |
| if (!status.isOk()) { |
| return Error() << "Failed to find keystore key..."; |
| } |
| |
| // On some earlier builds, we created this key on the Strongbox security level; |
| // we now use TEE keys instead (mostly for speed). It shouldn't matter since |
| // verified boot is protected by the TEE anyway. If the key happens to be on |
| // the wrong security level, delete it (this should happen just once). |
| if (keyEntryResponse.metadata.keySecurityLevel != SecurityLevel::TRUSTED_ENVIRONMENT) { |
| return Error() << "Found invalid keystore key with security level: " |
| << android::hardware::security::keymint::toString( |
| keyEntryResponse.metadata.keySecurityLevel); |
| } |
| |
| // Make sure this is an early boot key |
| bool foundBootLevel = false; |
| for (const auto& auth : keyEntryResponse.metadata.authorizations) { |
| if (auth.keyParameter.tag == Tag::MAX_BOOT_LEVEL) { |
| if (auth.keyParameter.value.get<KeyParameterValue::integer>() == mKeyBootLevel) { |
| foundBootLevel = true; |
| break; |
| } |
| } |
| } |
| if (!foundBootLevel) { |
| return Error() << "Found invalid keystore key without MAX_BOOT_LEVEL tag"; |
| } |
| |
| // If the key is still considered valid at this point, extract the public |
| // key from the certificate. Note that we cannot trust this public key, |
| // because it is a part of the keystore2 database, which can be modified by |
| // an attacker. So instead, when creating the key we HMAC the public key |
| // with a key of the same boot level, and verify the signature here. |
| auto cert = keyEntryResponse.metadata.certificate; |
| if (!cert) { |
| return Error() << "Key did not have a certificate."; |
| } |
| auto publicKey = extractPublicKeyFromX509(cert.value()); |
| if (!publicKey.ok()) { |
| return publicKey.error(); |
| } |
| std::string publicKeyString = {publicKey->begin(), publicKey->end()}; |
| |
| std::string signature; |
| if (!android::base::ReadFileToString(mSignedPubKeyPath, &signature)) { |
| return Error() << "Can't find signature for public key."; |
| } |
| |
| auto signatureValid = mHmacKey.verify(publicKeyString, signature); |
| if (!signatureValid.ok()) { |
| return Error() << "Signature of public key did not match."; |
| } |
| LOG(INFO) << "Verified public key signature."; |
| |
| return *publicKey; |
| } |
| |
| Result<std::vector<uint8_t>> KeystoreKey::getOrCreateKey() { |
| auto existingKey = verifyExistingKey(); |
| if (!existingKey.ok()) { |
| LOG(INFO) << existingKey.error().message(); |
| LOG(INFO) << "Existing keystore key not found or invalid, creating new key"; |
| return createKey(); |
| } |
| |
| return *existingKey; |
| } |
| |
| Result<SigningKey*> KeystoreKey::getInstance(const std::string& signedPubKeyPath, |
| const android::String16& keyAlias, int64_t keyNspace, |
| int keyBootLevel) { |
| auto keystoreKey = new KeystoreKey(signedPubKeyPath, keyAlias, keyNspace, keyBootLevel); |
| |
| if (!keystoreKey->initialize()) { |
| return Error() << "Failed to initialize keystore key."; |
| } else { |
| return keystoreKey; |
| } |
| } |
| |
| static std::vector<KeyParameter> getSignOpParameters() { |
| std::vector<KeyParameter> opParameters; |
| |
| KeyParameter algo; |
| algo.tag = Tag::ALGORITHM; |
| algo.value = KeyParameterValue::make<KeyParameterValue::algorithm>(Algorithm::RSA); |
| opParameters.push_back(algo); |
| |
| KeyParameter digest; |
| digest.tag = Tag::DIGEST; |
| digest.value = KeyParameterValue::make<KeyParameterValue::digest>(Digest::SHA_2_256); |
| opParameters.push_back(digest); |
| |
| KeyParameter padding; |
| padding.tag = Tag::PADDING; |
| padding.value = |
| KeyParameterValue::make<KeyParameterValue::paddingMode>(PaddingMode::RSA_PKCS1_1_5_SIGN); |
| opParameters.push_back(padding); |
| |
| KeyParameter purpose; |
| purpose.tag = Tag::PURPOSE; |
| purpose.value = KeyParameterValue::make<KeyParameterValue::keyPurpose>(KeyPurpose::SIGN); |
| opParameters.push_back(purpose); |
| |
| return opParameters; |
| } |
| |
| Result<std::string> KeystoreKey::sign(const std::string& message) const { |
| static auto opParameters = getSignOpParameters(); |
| CreateOperationResponse opResponse; |
| |
| auto status = mSecurityLevel->createOperation(mDescriptor, opParameters, false, &opResponse); |
| if (!status.isOk()) { |
| return Error() << "Failed to create keystore signing operation: " << status; |
| } |
| auto operation = opResponse.iOperation; |
| |
| std::optional<std::vector<uint8_t>> input{std::in_place, message.begin(), message.end()}; |
| std::optional<std::vector<uint8_t>> signature; |
| status = operation->finish(input, {}, &signature); |
| if (!status.isOk()) { |
| return Error() << "Failed to call keystore finish operation."; |
| } |
| |
| if (!signature.has_value()) { |
| return Error() << "Didn't receive a signature from keystore finish operation."; |
| } |
| |
| return std::string{signature.value().begin(), signature.value().end()}; |
| } |
| |
| Result<std::vector<uint8_t>> KeystoreKey::getPublicKey() const { |
| return mPublicKey; |
| } |