C++ AIDL on-device GateKeeper / SharedSecret impl
Because Keystore2 always requires valid auth tokens for user keys, this
copies and extends the existing in-guest GateKeeper implementation to
negotiate a shared secret key with Keymint in order to generate a
session key for signing auth tokens.
This implementation also uses AIDL rather than HIDL to interact with the
framework. It's also packaged in an APEX.
The files are cobbled together from a few sources:
- SoftGateKeeper.h is based on hardware/interfaces/gatekeeper/1.0/software/SoftGateKeeper.h
- GateKeeper.{cpp,h} are based on device/google/cuttlefish/guest/hals/gatekeeper/remote/remote_gatekeeper.{cpp,h}
- SharedSecret.{cpp,h} are based on device/google/cuttlefish/guest/hals/keymint/remote/remote_shared_secret.{cpp,h}
- Apex files are based on device/google/cuttlefish/guest/hals/keymint/rust/
Keymint modifications to use BOOT_TIME are lifted from
https://android-review.git.corp.google.com/c/platform/hardware/interfaces/+/2856649/6..8/security/keymint/aidl/default/ta/clock.rs#38
Bug: 332376454
Change-Id: I81845d5e6370bdddb1a24d67437964e03a5fb243
Test: Run with rust-nonsecure keymint on Cuttlefish
diff --git a/gatekeeper/aidl/software/SoftGateKeeper.h b/gatekeeper/aidl/software/SoftGateKeeper.h
new file mode 100644
index 0000000..305d997
--- /dev/null
+++ b/gatekeeper/aidl/software/SoftGateKeeper.h
@@ -0,0 +1,189 @@
+/*
+ * Copyright 2015 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.
+ *
+ */
+
+#ifndef SOFT_GATEKEEPER_H_
+#define SOFT_GATEKEEPER_H_
+
+extern "C" {
+#include <openssl/rand.h>
+#include <openssl/sha.h>
+
+#include <crypto_scrypt.h>
+}
+
+#include <memory>
+#include <unordered_map>
+
+#include <android-base/logging.h>
+#include <android-base/memory.h>
+#include <gatekeeper/gatekeeper.h>
+#include <keymaster/km_openssl/hmac.h>
+
+#include "SharedSecret.h"
+
+namespace gatekeeper {
+
+struct fast_hash_t {
+ uint64_t salt;
+ uint8_t digest[SHA256_DIGEST_LENGTH];
+};
+
+class SoftGateKeeper : public GateKeeper {
+ public:
+ static const uint32_t SIGNATURE_LENGTH_BYTES = 32;
+
+ // scrypt params
+ static const uint64_t N = 16384;
+ static const uint32_t r = 8;
+ static const uint32_t p = 1;
+
+ static const int MAX_UINT_32_CHARS = 11;
+
+ SoftGateKeeper(const ::aidl::android::hardware::security::sharedsecret::SoftSharedSecret&
+ shared_secret)
+ : shared_secret_(shared_secret) {
+ key_.reset(new uint8_t[SIGNATURE_LENGTH_BYTES]);
+ memset(key_.get(), 0, SIGNATURE_LENGTH_BYTES);
+ }
+
+ virtual ~SoftGateKeeper() {}
+
+ virtual bool GetAuthTokenKey(const uint8_t** auth_token_key, uint32_t* length) const {
+ if (auth_token_key == NULL || length == NULL) return false;
+ if (hmac_key_.key_material == nullptr) {
+ hmac_key_ = shared_secret_.HmacKey();
+ }
+ *auth_token_key = hmac_key_.key_material;
+ *length = hmac_key_.key_material_size;
+ return true;
+ }
+
+ virtual void GetPasswordKey(const uint8_t** password_key, uint32_t* length) {
+ if (password_key == NULL || length == NULL) return;
+ *password_key = key_.get();
+ *length = SIGNATURE_LENGTH_BYTES;
+ }
+
+ virtual void ComputePasswordSignature(uint8_t* signature, uint32_t signature_length,
+ const uint8_t*, uint32_t, const uint8_t* password,
+ uint32_t password_length, salt_t salt) const {
+ if (signature == NULL) return;
+ crypto_scrypt(password, password_length, reinterpret_cast<uint8_t*>(&salt), sizeof(salt), N,
+ r, p, signature, signature_length);
+ }
+
+ virtual void GetRandom(void* random, uint32_t requested_length) const {
+ if (random == NULL) return;
+ RAND_pseudo_bytes((uint8_t*)random, requested_length);
+ }
+
+ virtual void ComputeSignature(uint8_t* signature, uint32_t signature_length, const uint8_t* key,
+ uint32_t key_length, const uint8_t* message,
+ const uint32_t message_length) const {
+ if (signature == NULL) return;
+ keymaster::HmacSha256 hmac_calculator;
+ if (!hmac_calculator.Init(key, key_length)) {
+ LOG(ERROR) << "ComputeSignature: Failed to initialize hmac calculator";
+ return;
+ }
+ if (!hmac_calculator.Sign(message, message_length, signature, signature_length)) {
+ LOG(ERROR) << "ComputeSignature: failed to create hmac";
+ }
+ }
+
+ virtual uint64_t GetMillisecondsSinceBoot() const {
+ struct timespec time;
+ int res = clock_gettime(CLOCK_BOOTTIME, &time);
+ if (res < 0) return 0;
+ return (time.tv_sec * 1000) + (time.tv_nsec / 1000 / 1000);
+ }
+
+ virtual bool IsHardwareBacked() const { return false; }
+
+ virtual bool GetFailureRecord(uint32_t uid, secure_id_t user_id, failure_record_t* record,
+ bool /* secure */) {
+ failure_record_t* stored = &failure_map_[uid];
+ if (user_id != stored->secure_user_id) {
+ stored->secure_user_id = user_id;
+ stored->last_checked_timestamp = 0;
+ stored->failure_counter = 0;
+ }
+ memcpy(record, stored, sizeof(*record));
+ return true;
+ }
+
+ virtual bool ClearFailureRecord(uint32_t uid, secure_id_t user_id, bool /* secure */) {
+ failure_record_t* stored = &failure_map_[uid];
+ stored->secure_user_id = user_id;
+ stored->last_checked_timestamp = 0;
+ stored->failure_counter = 0;
+ return true;
+ }
+
+ virtual bool WriteFailureRecord(uint32_t uid, failure_record_t* record, bool /* secure */) {
+ failure_map_[uid] = *record;
+ return true;
+ }
+
+ fast_hash_t ComputeFastHash(const SizedBuffer& password, uint64_t salt) {
+ fast_hash_t fast_hash;
+ size_t digest_size = password.size() + sizeof(salt);
+ std::unique_ptr<uint8_t[]> digest(new uint8_t[digest_size]);
+ memcpy(digest.get(), &salt, sizeof(salt));
+ memcpy(digest.get() + sizeof(salt), password.Data<uint8_t>(), password.size());
+
+ SHA256(digest.get(), digest_size, (uint8_t*)&fast_hash.digest);
+
+ fast_hash.salt = salt;
+ return fast_hash;
+ }
+
+ bool VerifyFast(const fast_hash_t& fast_hash, const SizedBuffer& password) {
+ fast_hash_t computed = ComputeFastHash(password, fast_hash.salt);
+ return memcmp(computed.digest, fast_hash.digest, SHA256_DIGEST_LENGTH) == 0;
+ }
+
+ bool DoVerify(const password_handle_t* expected_handle, const SizedBuffer& password) {
+ uint64_t user_id = android::base::get_unaligned<secure_id_t>(&expected_handle->user_id);
+ FastHashMap::const_iterator it = fast_hash_map_.find(user_id);
+ if (it != fast_hash_map_.end() && VerifyFast(it->second, password)) {
+ return true;
+ } else {
+ if (GateKeeper::DoVerify(expected_handle, password)) {
+ uint64_t salt;
+ GetRandom(&salt, sizeof(salt));
+ fast_hash_map_[user_id] = ComputeFastHash(password, salt);
+ return true;
+ }
+ }
+
+ return false;
+ }
+
+ private:
+ typedef std::unordered_map<uint32_t, failure_record_t> FailureRecordMap;
+ typedef std::unordered_map<uint64_t, fast_hash_t> FastHashMap;
+
+ const ::aidl::android::hardware::security::sharedsecret::SoftSharedSecret& shared_secret_;
+ std::unique_ptr<uint8_t[]> key_;
+ FailureRecordMap failure_map_;
+ FastHashMap fast_hash_map_;
+ mutable ::keymaster::KeymasterKeyBlob hmac_key_;
+};
+} // namespace gatekeeper
+
+#endif // SOFT_GATEKEEPER_H_