Implement key attestation using AndroidKeystore. (f1e57387) · Commits · e / os / android_packages_modules_Bluetooth

system/btif/Android.bp

+15 −0

Original line number	Diff line number	Diff line
		@@ -24,6 +24,8 @@ btifCommonIncludes = [
		"packages/modules/Bluetooth/system/utils/include",
		"packages/modules/Bluetooth/system/include",
		"system/libhwbinder/include",
		"system/security/keystore/include",
		"hardware/interfaces/keymaster/4.0/support/include",
		]

		// libbtif static library for target
		@@ -71,6 +73,7 @@ cc_library_static {
		"src/btif_hf_client.cc",
		"src/btif_hh.cc",
		"src/btif_hd.cc",
		"src/btif_keystore.cc",
		"src/btif_mce.cc",
		"src/btif_pan.cc",
		"src/btif_profile_queue.cc",
		@@ -101,6 +104,12 @@ cc_library_static {
		"libhwbinder",
		"libutils",
		"libcrypto",
		"android.hardware.keymaster@4.0",
		"android.hardware.keymaster@3.0",
		"libkeymaster4support",
		"libkeystore_aidl",
		"libkeystore_binder",
		"libkeystore_parcelables",
		],
		whole_static_libs: [
		"avrcp-target-service",
		@@ -133,6 +142,12 @@ cc_test {
		"libprocessgroup",
		"libutils",
		"libcrypto",
		"android.hardware.keymaster@4.0",
		"android.hardware.keymaster@3.0",
		"libkeymaster4support",
		"libkeystore_aidl",
		"libkeystore_binder",
		"libkeystore_parcelables",
		],
		static_libs: [
		"libbt-bta",

system/btif/include/btif_keystore.h

0 → 100644

+39 −0

Original line number	Diff line number	Diff line
		/******************************************************************************
		*
		* Copyright 2019 Google, Inc.
		*
		* 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 <base/logging.h>
		#include <keystore/keystore_client_impl.h>

		#include "osi/include/alarm.h"
		#include "osi/include/allocator.h"
		#include "osi/include/compat.h"
		#include "osi/include/config.h"
		#include "osi/include/log.h"
		#include "osi/include/osi.h"
		#include "osi/include/properties.h"

		using namespace keystore;

		class BtifKeystore {
		public:
		BtifKeystore();
		~BtifKeystore();
		int Encrypt(const std::string& hash, const std::string& output_filename,
		int32_t flags);
		std::string Decrypt(const std::string& input_filename);
		};

system/btif/src/btif_config.cc

+102 −4

Original line number	Diff line number	Diff line
		@@ -23,10 +23,12 @@
		#include <base/logging.h>
		#include <ctype.h>
		#include <openssl/rand.h>
		#include <openssl/sha.h>
		#include <stdio.h>
		#include <string.h>
		#include <time.h>
		#include <unistd.h>
		#include <sstream>
		#include <string>

		#include <mutex>
		@@ -36,6 +38,7 @@
		#include "btif_api.h"
		#include "btif_common.h"
		#include "btif_config_transcode.h"
		#include "btif_keystore.h"
		#include "btif_util.h"
		#include "common/address_obfuscator.h"
		#include "osi/include/alarm.h"
		@@ -66,6 +69,8 @@ static const char* CONFIG_LEGACY_FILE_PATH = "bt_config.xml";
		#else // !defined(OS_GENERIC)
		static const char* CONFIG_FILE_PATH = "/data/misc/bluedroid/bt_config.conf";
		static const char* CONFIG_BACKUP_PATH = "/data/misc/bluedroid/bt_config.bak";
		static const char* CONFIG_FILE_CHECKSUM_PATH = "/data/misc/bluedroid/bt_config.conf.encrypted-checksum";
		static const char* CONFIG_BACKUP_CHECKSUM_PATH = "/data/misc/bluedroid/bt_config.bak.encrypted-checksum";
		static const char* CONFIG_LEGACY_FILE_PATH =
		"/data/misc/bluedroid/bt_config.xml";
		#endif // defined(OS_GENERIC)
		@@ -77,7 +82,14 @@ static bool is_factory_reset(void);
		static void delete_config_files(void);
		static void btif_config_remove_unpaired(config_t* config);
		static void btif_config_remove_restricted(config_t* config);
		static std::unique_ptr<config_t> btif_config_open(const char* filename);
		static std::unique_ptr<config_t> btif_config_open(const char* filename, const char* checksum_filename);

		// Key attestation
		static std::string hash_file(const char* filename);
		static std::string read_checksum_file(const char* filename);
		static void write_checksum_file(const char* filename, const std::string hash);
		static bool verify_hash(const std::string current_hash,
		const std::string stored_hash);

		static enum ConfigSource {
		NOT_LOADED,
		@@ -157,6 +169,7 @@ static void read_or_set_metrics_salt() {
		static std::recursive_mutex config_lock; // protects operations on \|config\|.
		static std::unique_ptr<config_t> config;
		static alarm_t* config_timer;
		static BtifKeystore btifKeystore;

		// Module lifecycle functions

		@@ -167,12 +180,13 @@ static future_t* init(void) {

		std::string file_source;

		config = btif_config_open(CONFIG_FILE_PATH);
		config = btif_config_open(CONFIG_FILE_PATH, CONFIG_FILE_CHECKSUM_PATH);
		btif_config_source = ORIGINAL;
		if (!config) {
		LOG_WARN(LOG_TAG, "%s unable to load config file: %s; using backup.",
		__func__, CONFIG_FILE_PATH);
		config = btif_config_open(CONFIG_BACKUP_PATH);
		remove(CONFIG_FILE_CHECKSUM_PATH);
		config = btif_config_open(CONFIG_BACKUP_PATH, CONFIG_BACKUP_CHECKSUM_PATH);
		btif_config_source = BACKUP;
		file_source = "Backup";
		}
		@@ -180,6 +194,7 @@ static future_t* init(void) {
		LOG_WARN(LOG_TAG,
		"%s unable to load backup; attempting to transcode legacy file.",
		__func__);
		remove(CONFIG_BACKUP_CHECKSUM_PATH);
		config = btif_config_transcode(CONFIG_LEGACY_FILE_PATH);
		btif_config_source = LEGACY;
		file_source = "Legacy";
		@@ -239,7 +254,25 @@ error:
		return future_new_immediate(FUTURE_FAIL);
		}

		static std::unique_ptr<config_t> btif_config_open(const char* filename) {
		static std::unique_ptr<config_t> btif_config_open(const char* filename, const char* checksum_filename) {
		// START KEY ATTESTATION
		// Get hash of current file
		std::string current_hash = hash_file(filename);
		// Get stored hash
		std::string stored_hash = read_checksum_file(checksum_filename);
		if (stored_hash.empty()) {
		LOG(ERROR) << __func__ << ": stored_hash=<empty>";
		if (!current_hash.empty()) {
		write_checksum_file(checksum_filename, current_hash);
		stored_hash = read_checksum_file(checksum_filename);
		}
		}
		// Compare hashes
		if (!verify_hash(current_hash, stored_hash)) {
		return nullptr;
		}
		// END KEY ATTESTATION

		std::unique_ptr<config_t> config = config_new(filename);
		if (!config) return nullptr;

		@@ -471,6 +504,13 @@ bool btif_config_clear(void) {

		bool ret = config_save(*config, CONFIG_FILE_PATH);
		btif_config_source = RESET;

		// Save encrypted hash
		std::string current_hash = hash_file(CONFIG_FILE_PATH);
		if (!current_hash.empty()) {
		write_checksum_file(CONFIG_FILE_CHECKSUM_PATH, current_hash);
		}

		return ret;
		}

		@@ -488,9 +528,15 @@ static void btif_config_write(UNUSED_ATTR uint16_t event,

		std::unique_lock<std::recursive_mutex> lock(config_lock);
		rename(CONFIG_FILE_PATH, CONFIG_BACKUP_PATH);
		rename(CONFIG_FILE_CHECKSUM_PATH, CONFIG_BACKUP_CHECKSUM_PATH);
		std::unique_ptr<config_t> config_paired = config_new_clone(*config);
		btif_config_remove_unpaired(config_paired.get());
		config_save(*config_paired, CONFIG_FILE_PATH);
		// Save hash
		std::string current_hash = hash_file(CONFIG_FILE_PATH);
		if (!current_hash.empty()) {
		write_checksum_file(CONFIG_FILE_CHECKSUM_PATH, current_hash);
		}
		}

		static void btif_config_remove_unpaired(config_t* conf) {
		@@ -582,5 +628,57 @@ static bool is_factory_reset(void) {
		static void delete_config_files(void) {
		remove(CONFIG_FILE_PATH);
		remove(CONFIG_BACKUP_PATH);
		remove(CONFIG_FILE_CHECKSUM_PATH);
		remove(CONFIG_BACKUP_CHECKSUM_PATH);
		osi_property_set("persist.bluetooth.factoryreset", "false");
		}

		static std::string hash_file(const char* filename) {
		FILE* fp = fopen(filename, "rb");
		if (!fp) {
		LOG(ERROR) << __func__ << ": unable to open config file: '" << filename
		<< "': " << strerror(errno);
		return "";
		}
		unsigned char hash[SHA256_DIGEST_LENGTH];
		SHA256_CTX sha256;
		SHA256_Init(&sha256);
		const int bufSize = 400 * 10; // initial file is ~400B
		std::byte* buffer = (std::byte*) osi_calloc(bufSize);
		int bytesRead = 0;
		if (!buffer) return "";
		while ((bytesRead = fread(buffer, 1, bufSize, fp))) {
		SHA256_Update(&sha256, buffer, bytesRead);
		}
		SHA256_Final(hash, &sha256);
		std::stringstream ss;
		for (int i = 0; i < SHA256_DIGEST_LENGTH; i++) {
		ss << std::hex << std::setw(2) << std::setfill('0') << (int)hash[i];
		}
		fclose(fp);
		osi_free(buffer);
		return ss.str();
		}

		static std::string read_checksum_file(const char* checksum_filename) {
		// Ensure file exists
		FILE* fp = fopen(checksum_filename, "rb");
		if (!fp) {
		return "";
		} else {
		fclose(fp);
		}
		std::string output = btifKeystore.Decrypt(checksum_filename);
		return output;
		}

		static void write_checksum_file(const char* checksum_filename, std::string hash) {
		int result = btifKeystore.Encrypt(hash, checksum_filename, 0);
		if (result != 0) {
		LOG(ERROR) << "Failed writing checksum!";
		}
		}

		static bool verify_hash(std::string current_hash, std::string stored_hash) {
		return current_hash.compare(stored_hash) == 0;
		}

system/btif/src/btif_keystore.cc

0 → 100644

+146 −0

Original line number	Diff line number	Diff line
		/******************************************************************************
		*
		* Copyright 2019 Google, Inc.
		*
		* 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 "bt_btif_keystore"

		#include "btif_keystore.h"
		#include "osi/include/properties.h"

		#include <base/files/file_util.h>
		#include <base/logging.h>
		#include <base/strings/string_number_conversions.h>
		#include <base/strings/string_split.h>
		#include <base/strings/string_util.h>
		#include <base/strings/utf_string_conversions.h>
		#include <sys/stat.h>

		using namespace keystore;

		static std::unique_ptr<keystore::KeystoreClient> CreateKeystoreInstance(void);
		static void WriteFile(const std::string& filename, const std::string& content);
		static std::string ReadFile(const std::string& filename);
		static int GenerateKey(const std::string& name, int32_t flags, bool auth_bound);
		static bool DoesKeyExist(const std::string& name);

		const std::string FILE_SUFFIX = ".encrypted-checksum";
		const std::string CIPHER_ALGORITHM = "AES/GCM/NoPadding";
		const std::string DIGEST_ALGORITHM = "SHA-256";
		const std::string KEY_STORE = "AndroidKeystore";

		std::unique_ptr<KeystoreClient> keystoreClient;

		BtifKeystore::BtifKeystore() { keystoreClient = CreateKeystoreInstance(); }

		BtifKeystore::~BtifKeystore() {
		// Using a smart pointer, does it delete itself?
		// delete keystoreClient;
		}

		int BtifKeystore::Encrypt(const std::string& hash,
		const std::string& output_filename, int32_t flags) {
		std::string output;
		if (!DoesKeyExist(KEY_STORE)) {
		GenerateKey(KEY_STORE, 0, false);
		}
		char is_unittest[PROPERTY_VALUE_MAX] = {0};
		osi_property_get("debug.bluetooth.unittest", is_unittest, "false");
		if (strcmp(is_unittest, "false") == 0) {
		if (!keystoreClient->encryptWithAuthentication(KEY_STORE, hash, flags,
		&output)) {
		LOG(ERROR) << "EncryptWithAuthentication failed.\n";
		return 1;
		}
		}
		WriteFile(output_filename, output);
		return 0;
		}

		std::string BtifKeystore::Decrypt(const std::string& input_filename) {
		std::string input = ReadFile(input_filename);
		std::string output;

		char is_unittest[PROPERTY_VALUE_MAX] = {0};
		osi_property_get("debug.bluetooth.unittest", is_unittest, "false");
		if (strcmp(is_unittest, "false") == 0) {
		if (!keystoreClient->decryptWithAuthentication(KEY_STORE, input, &output)) {
		LOG(ERROR) << "DecryptWithAuthentication failed.\n";
		}
		}
		return output;
		}

		static std::string ReadFile(const std::string& filename) {
		std::string content;
		struct stat buffer;
		if (stat(filename.c_str(), &buffer) == 0) {
		base::FilePath path(filename);
		if (!base::ReadFileToString(path, &content)) {
		LOG(ERROR) << "ReadFile failed.\n" << filename.c_str();
		}
		}
		return content;
		}

		static void WriteFile(const std::string& filename, const std::string& content) {
		base::FilePath path(filename);
		int size = content.size();
		if (base::WriteFile(path, content.data(), size) != size) {
		LOG(ERROR) << "WriteFile failed.\n" << filename.c_str();
		}
		}

		// Note: auth_bound keys created with this tool will not be usable.
		static int GenerateKey(const std::string& name, int32_t flags,
		bool auth_bound) {
		AuthorizationSetBuilder params;
		params.RsaSigningKey(2048, 65537)
		.Digest(Digest::SHA_2_224)
		.Digest(Digest::SHA_2_256)
		.Digest(Digest::SHA_2_384)
		.Digest(Digest::SHA_2_512)
		.Padding(PaddingMode::RSA_PKCS1_1_5_SIGN)
		.Padding(PaddingMode::RSA_PSS);
		if (auth_bound) {
		// Gatekeeper normally generates the secure user id.
		// Using zero allows the key to be created, but it will not be usuable.
		params.Authorization(TAG_USER_SECURE_ID, 0);
		} else {
		params.Authorization(TAG_NO_AUTH_REQUIRED);
		}
		AuthorizationSet hardware_enforced_characteristics;
		AuthorizationSet software_enforced_characteristics;

		char is_unittest[PROPERTY_VALUE_MAX] = {0};
		osi_property_get("debug.bluetooth.unittest", is_unittest, "false");
		if (strcmp(is_unittest, "false") != 0) {
		return -1;
		}
		auto result = keystoreClient->generateKey(name, params, flags,
		&hardware_enforced_characteristics,
		&software_enforced_characteristics);
		return result.getErrorCode();
		}

		static bool DoesKeyExist(const std::string& name) {
		return keystoreClient->doesKeyExist(name) ? true : false;
		}

		static std::unique_ptr<KeystoreClient> CreateKeystoreInstance(void) {
		return std::unique_ptr<KeystoreClient>(
		static_cast<KeystoreClient*>(new KeystoreClientImpl));
		}

system/main/Android.bp

+8 −0

Original line number	Diff line number	Diff line
		@@ -35,6 +35,8 @@ cc_library_shared {
		"packages/modules/Bluetooth/system/embdrv/sbc/encoder/include",
		"packages/modules/Bluetooth/system/embdrv/sbc/decoder/include",
		"packages/modules/Bluetooth/system/utils/include",
		"system/security/keystore/include",
		"hardware/interfaces/keymaster/4.0/support/include",
		],
		logtags: ["../../EventLogTags.logtags"],
		shared_libs: [
		@@ -53,6 +55,12 @@ cc_library_shared {
		"libtinyxml2",
		"libz",
		"libcrypto",
		"android.hardware.keymaster@4.0",
		"android.hardware.keymaster@3.0",
		"libkeymaster4support",
		"libkeystore_aidl",
		"libkeystore_binder",
		"libkeystore_parcelables",
		],
		static_libs: [
		"libbt-sbc-decoder",