1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include <keymaster/keymaster_enforcement.h> 18 19 #include <assert.h> 20 #include <limits.h> 21 #include <string.h> 22 23 #include <openssl/evp.h> 24 25 #include <hardware/hw_auth_token.h> 26 #include <keymaster/android_keymaster_utils.h> 27 #include <keymaster/logger.h> 28 29 #include "List.h" 30 31 using android::List; 32 33 namespace keymaster { 34 35 class AccessTimeMap { 36 public: 37 explicit AccessTimeMap(uint32_t max_size) : max_size_(max_size) {} 38 39 /* If the key is found, returns true and fills \p last_access_time. If not found returns 40 * false. */ 41 bool LastKeyAccessTime(km_id_t keyid, uint32_t* last_access_time) const; 42 43 /* Updates the last key access time with the currentTime parameter. Adds the key if 44 * needed, returning false if key cannot be added because list is full. */ 45 bool UpdateKeyAccessTime(km_id_t keyid, uint32_t current_time, uint32_t timeout); 46 47 private: 48 struct AccessTime { 49 km_id_t keyid; 50 uint32_t access_time; 51 uint32_t timeout; 52 }; 53 android::List<AccessTime> last_access_list_; 54 const uint32_t max_size_; 55 }; 56 57 class AccessCountMap { 58 public: 59 explicit AccessCountMap(uint32_t max_size) : max_size_(max_size) {} 60 61 /* If the key is found, returns true and fills \p count. If not found returns 62 * false. */ 63 bool KeyAccessCount(km_id_t keyid, uint32_t* count) const; 64 65 /* Increments key access count, adding an entry if the key has never been used. Returns 66 * false if the list has reached maximum size. */ 67 bool IncrementKeyAccessCount(km_id_t keyid); 68 69 private: 70 struct AccessCount { 71 km_id_t keyid; 72 uint64_t access_count; 73 }; 74 android::List<AccessCount> access_count_list_; 75 const uint32_t max_size_; 76 }; 77 78 bool is_public_key_algorithm(const AuthorizationSet& auth_set) { 79 keymaster_algorithm_t algorithm; 80 return auth_set.GetTagValue(TAG_ALGORITHM, &algorithm) && 81 (algorithm == KM_ALGORITHM_RSA || algorithm == KM_ALGORITHM_EC); 82 } 83 84 static keymaster_error_t authorized_purpose(const keymaster_purpose_t purpose, 85 const AuthorizationSet& auth_set) { 86 switch (purpose) { 87 case KM_PURPOSE_VERIFY: 88 case KM_PURPOSE_ENCRYPT: 89 case KM_PURPOSE_SIGN: 90 case KM_PURPOSE_DECRYPT: 91 if (auth_set.Contains(TAG_PURPOSE, purpose)) 92 return KM_ERROR_OK; 93 return KM_ERROR_INCOMPATIBLE_PURPOSE; 94 95 default: 96 return KM_ERROR_UNSUPPORTED_PURPOSE; 97 } 98 } 99 100 inline bool is_origination_purpose(keymaster_purpose_t purpose) { 101 return purpose == KM_PURPOSE_ENCRYPT || purpose == KM_PURPOSE_SIGN; 102 } 103 104 inline bool is_usage_purpose(keymaster_purpose_t purpose) { 105 return purpose == KM_PURPOSE_DECRYPT || purpose == KM_PURPOSE_VERIFY; 106 } 107 108 KeymasterEnforcement::KeymasterEnforcement(uint32_t max_access_time_map_size, 109 uint32_t max_access_count_map_size) 110 : access_time_map_(new (std::nothrow) AccessTimeMap(max_access_time_map_size)), 111 access_count_map_(new (std::nothrow) AccessCountMap(max_access_count_map_size)) {} 112 113 KeymasterEnforcement::~KeymasterEnforcement() { 114 delete access_time_map_; 115 delete access_count_map_; 116 } 117 118 keymaster_error_t KeymasterEnforcement::AuthorizeOperation(const keymaster_purpose_t purpose, 119 const km_id_t keyid, 120 const AuthorizationSet& auth_set, 121 const AuthorizationSet& operation_params, 122 keymaster_operation_handle_t op_handle, 123 bool is_begin_operation) { 124 if (is_public_key_algorithm(auth_set)) { 125 switch (purpose) { 126 case KM_PURPOSE_ENCRYPT: 127 case KM_PURPOSE_VERIFY: 128 /* Public key operations are always authorized. */ 129 return KM_ERROR_OK; 130 131 case KM_PURPOSE_DECRYPT: 132 case KM_PURPOSE_SIGN: 133 case KM_PURPOSE_DERIVE_KEY: 134 break; 135 }; 136 }; 137 138 if (is_begin_operation) 139 return AuthorizeBegin(purpose, keyid, auth_set, operation_params); 140 else 141 return AuthorizeUpdateOrFinish(auth_set, operation_params, op_handle); 142 } 143 144 // For update and finish the only thing to check is user authentication, and then only if it's not 145 // timeout-based. 146 keymaster_error_t 147 KeymasterEnforcement::AuthorizeUpdateOrFinish(const AuthorizationSet& auth_set, 148 const AuthorizationSet& operation_params, 149 keymaster_operation_handle_t op_handle) { 150 int auth_type_index = -1; 151 for (size_t pos = 0; pos < auth_set.size(); ++pos) { 152 switch (auth_set[pos].tag) { 153 case KM_TAG_NO_AUTH_REQUIRED: 154 case KM_TAG_AUTH_TIMEOUT: 155 // If no auth is required or if auth is timeout-based, we have nothing to check. 156 return KM_ERROR_OK; 157 158 case KM_TAG_USER_AUTH_TYPE: 159 auth_type_index = pos; 160 break; 161 162 default: 163 break; 164 } 165 } 166 167 // Note that at this point we should be able to assume that authentication is required, because 168 // authentication is required if KM_TAG_NO_AUTH_REQUIRED is absent. However, there are legacy 169 // keys which have no authentication-related tags, so we assume that absence is equivalent to 170 // presence of KM_TAG_NO_AUTH_REQUIRED. 171 // 172 // So, if we found KM_TAG_USER_AUTH_TYPE or if we find KM_TAG_USER_SECURE_ID then authentication 173 // is required. If we find neither, then we assume authentication is not required and return 174 // success. 175 bool authentication_required = (auth_type_index != -1); 176 for (auto& param : auth_set) { 177 if (param.tag == KM_TAG_USER_SECURE_ID) { 178 authentication_required = true; 179 int auth_timeout_index = -1; 180 if (AuthTokenMatches(auth_set, operation_params, param.long_integer, auth_type_index, 181 auth_timeout_index, op_handle, false /* is_begin_operation */)) 182 return KM_ERROR_OK; 183 } 184 } 185 186 if (authentication_required) 187 return KM_ERROR_KEY_USER_NOT_AUTHENTICATED; 188 189 return KM_ERROR_OK; 190 } 191 192 keymaster_error_t KeymasterEnforcement::AuthorizeBegin(const keymaster_purpose_t purpose, 193 const km_id_t keyid, 194 const AuthorizationSet& auth_set, 195 const AuthorizationSet& operation_params) { 196 // Find some entries that may be needed to handle KM_TAG_USER_SECURE_ID 197 int auth_timeout_index = -1; 198 int auth_type_index = -1; 199 int no_auth_required_index = -1; 200 for (size_t pos = 0; pos < auth_set.size(); ++pos) { 201 switch (auth_set[pos].tag) { 202 case KM_TAG_AUTH_TIMEOUT: 203 auth_timeout_index = pos; 204 break; 205 case KM_TAG_USER_AUTH_TYPE: 206 auth_type_index = pos; 207 break; 208 case KM_TAG_NO_AUTH_REQUIRED: 209 no_auth_required_index = pos; 210 break; 211 default: 212 break; 213 } 214 } 215 216 keymaster_error_t error = authorized_purpose(purpose, auth_set); 217 if (error != KM_ERROR_OK) 218 return error; 219 220 // If successful, and if key has a min time between ops, this will be set to the time limit 221 uint32_t min_ops_timeout = UINT32_MAX; 222 223 bool update_access_count = false; 224 bool caller_nonce_authorized_by_key = false; 225 bool authentication_required = false; 226 bool auth_token_matched = false; 227 228 for (auto& param : auth_set) { 229 230 // KM_TAG_PADDING_OLD and KM_TAG_DIGEST_OLD aren't actually members of the enum, so we can't 231 // switch on them. There's nothing to validate for them, though, so just ignore them. 232 if (param.tag == KM_TAG_PADDING_OLD || param.tag == KM_TAG_DIGEST_OLD) 233 continue; 234 235 switch (param.tag) { 236 237 case KM_TAG_ACTIVE_DATETIME: 238 if (!activation_date_valid(param.date_time)) 239 return KM_ERROR_KEY_NOT_YET_VALID; 240 break; 241 242 case KM_TAG_ORIGINATION_EXPIRE_DATETIME: 243 if (is_origination_purpose(purpose) && expiration_date_passed(param.date_time)) 244 return KM_ERROR_KEY_EXPIRED; 245 break; 246 247 case KM_TAG_USAGE_EXPIRE_DATETIME: 248 if (is_usage_purpose(purpose) && expiration_date_passed(param.date_time)) 249 return KM_ERROR_KEY_EXPIRED; 250 break; 251 252 case KM_TAG_MIN_SECONDS_BETWEEN_OPS: 253 min_ops_timeout = param.integer; 254 if (!MinTimeBetweenOpsPassed(min_ops_timeout, keyid)) 255 return KM_ERROR_KEY_RATE_LIMIT_EXCEEDED; 256 break; 257 258 case KM_TAG_MAX_USES_PER_BOOT: 259 update_access_count = true; 260 if (!MaxUsesPerBootNotExceeded(keyid, param.integer)) 261 return KM_ERROR_KEY_MAX_OPS_EXCEEDED; 262 break; 263 264 case KM_TAG_USER_SECURE_ID: 265 if (no_auth_required_index != -1) { 266 // Key has both KM_TAG_USER_SECURE_ID and KM_TAG_NO_AUTH_REQUIRED 267 return KM_ERROR_INVALID_KEY_BLOB; 268 } 269 270 if (auth_timeout_index != -1) { 271 authentication_required = true; 272 if (AuthTokenMatches(auth_set, operation_params, param.long_integer, 273 auth_type_index, auth_timeout_index, 0 /* op_handle */, 274 true /* is_begin_operation */)) 275 auth_token_matched = true; 276 } 277 break; 278 279 case KM_TAG_CALLER_NONCE: 280 caller_nonce_authorized_by_key = true; 281 break; 282 283 /* Tags should never be in key auths. */ 284 case KM_TAG_INVALID: 285 case KM_TAG_AUTH_TOKEN: 286 case KM_TAG_ROOT_OF_TRUST: 287 case KM_TAG_APPLICATION_DATA: 288 case KM_TAG_ATTESTATION_CHALLENGE: 289 case KM_TAG_ATTESTATION_APPLICATION_ID: 290 case KM_TAG_ATTESTATION_ID_BRAND: 291 case KM_TAG_ATTESTATION_ID_DEVICE: 292 case KM_TAG_ATTESTATION_ID_PRODUCT: 293 case KM_TAG_ATTESTATION_ID_SERIAL: 294 case KM_TAG_ATTESTATION_ID_IMEI: 295 case KM_TAG_ATTESTATION_ID_MEID: 296 case KM_TAG_ATTESTATION_ID_MANUFACTURER: 297 case KM_TAG_ATTESTATION_ID_MODEL: 298 return KM_ERROR_INVALID_KEY_BLOB; 299 300 /* Tags used for cryptographic parameters in keygen. Nothing to enforce. */ 301 case KM_TAG_PURPOSE: 302 case KM_TAG_ALGORITHM: 303 case KM_TAG_KEY_SIZE: 304 case KM_TAG_BLOCK_MODE: 305 case KM_TAG_DIGEST: 306 case KM_TAG_MAC_LENGTH: 307 case KM_TAG_PADDING: 308 case KM_TAG_NONCE: 309 case KM_TAG_MIN_MAC_LENGTH: 310 case KM_TAG_KDF: 311 case KM_TAG_EC_CURVE: 312 313 /* Tags not used for operations. */ 314 case KM_TAG_BLOB_USAGE_REQUIREMENTS: 315 case KM_TAG_EXPORTABLE: 316 317 /* Algorithm specific parameters not used for access control. */ 318 case KM_TAG_RSA_PUBLIC_EXPONENT: 319 case KM_TAG_ECIES_SINGLE_HASH_MODE: 320 321 /* Informational tags. */ 322 case KM_TAG_CREATION_DATETIME: 323 case KM_TAG_ORIGIN: 324 case KM_TAG_ROLLBACK_RESISTANT: 325 326 /* Tags handled when KM_TAG_USER_SECURE_ID is handled */ 327 case KM_TAG_NO_AUTH_REQUIRED: 328 case KM_TAG_USER_AUTH_TYPE: 329 case KM_TAG_AUTH_TIMEOUT: 330 331 /* Tag to provide data to operations. */ 332 case KM_TAG_ASSOCIATED_DATA: 333 334 /* Tags that are implicitly verified by secure side */ 335 case KM_TAG_ALL_APPLICATIONS: 336 case KM_TAG_APPLICATION_ID: 337 case KM_TAG_OS_VERSION: 338 case KM_TAG_OS_PATCHLEVEL: 339 340 /* Ignored pending removal */ 341 case KM_TAG_USER_ID: 342 case KM_TAG_ALL_USERS: 343 344 /* TODO(swillden): Handle these */ 345 case KM_TAG_INCLUDE_UNIQUE_ID: 346 case KM_TAG_UNIQUE_ID: 347 case KM_TAG_RESET_SINCE_ID_ROTATION: 348 case KM_TAG_ALLOW_WHILE_ON_BODY: 349 break; 350 351 case KM_TAG_BOOTLOADER_ONLY: 352 return KM_ERROR_INVALID_KEY_BLOB; 353 } 354 } 355 356 if (authentication_required && !auth_token_matched) { 357 LOG_E("Auth required but no matching auth token found", 0); 358 return KM_ERROR_KEY_USER_NOT_AUTHENTICATED; 359 } 360 361 if (!caller_nonce_authorized_by_key && is_origination_purpose(purpose) && 362 operation_params.find(KM_TAG_NONCE) != -1) 363 return KM_ERROR_CALLER_NONCE_PROHIBITED; 364 365 if (min_ops_timeout != UINT32_MAX) { 366 if (!access_time_map_) { 367 LOG_S("Rate-limited keys table not allocated. Rate-limited keys disabled", 0); 368 return KM_ERROR_MEMORY_ALLOCATION_FAILED; 369 } 370 371 if (!access_time_map_->UpdateKeyAccessTime(keyid, get_current_time(), min_ops_timeout)) { 372 LOG_E("Rate-limited keys table full. Entries will time out.", 0); 373 return KM_ERROR_TOO_MANY_OPERATIONS; 374 } 375 } 376 377 if (update_access_count) { 378 if (!access_count_map_) { 379 LOG_S("Usage-count limited keys tabel not allocated. Count-limited keys disabled", 0); 380 return KM_ERROR_MEMORY_ALLOCATION_FAILED; 381 } 382 383 if (!access_count_map_->IncrementKeyAccessCount(keyid)) { 384 LOG_E("Usage count-limited keys table full, until reboot.", 0); 385 return KM_ERROR_TOO_MANY_OPERATIONS; 386 } 387 } 388 389 return KM_ERROR_OK; 390 } 391 392 class EvpMdCtx { 393 public: 394 EvpMdCtx() { EVP_MD_CTX_init(&ctx_); } 395 ~EvpMdCtx() { EVP_MD_CTX_cleanup(&ctx_); } 396 397 EVP_MD_CTX* get() { return &ctx_; } 398 399 private: 400 EVP_MD_CTX ctx_; 401 }; 402 403 /* static */ 404 bool KeymasterEnforcement::CreateKeyId(const keymaster_key_blob_t& key_blob, km_id_t* keyid) { 405 EvpMdCtx ctx; 406 407 uint8_t hash[EVP_MAX_MD_SIZE]; 408 unsigned int hash_len; 409 if (EVP_DigestInit_ex(ctx.get(), EVP_sha256(), nullptr /* ENGINE */) && 410 EVP_DigestUpdate(ctx.get(), key_blob.key_material, key_blob.key_material_size) && 411 EVP_DigestFinal_ex(ctx.get(), hash, &hash_len)) { 412 assert(hash_len >= sizeof(*keyid)); 413 memcpy(keyid, hash, sizeof(*keyid)); 414 return true; 415 } 416 417 return false; 418 } 419 420 bool KeymasterEnforcement::MinTimeBetweenOpsPassed(uint32_t min_time_between, const km_id_t keyid) { 421 if (!access_time_map_) 422 return false; 423 424 uint32_t last_access_time; 425 if (!access_time_map_->LastKeyAccessTime(keyid, &last_access_time)) 426 return true; 427 return min_time_between <= static_cast<int64_t>(get_current_time()) - last_access_time; 428 } 429 430 bool KeymasterEnforcement::MaxUsesPerBootNotExceeded(const km_id_t keyid, uint32_t max_uses) { 431 if (!access_count_map_) 432 return false; 433 434 uint32_t key_access_count; 435 if (!access_count_map_->KeyAccessCount(keyid, &key_access_count)) 436 return true; 437 return key_access_count < max_uses; 438 } 439 440 bool KeymasterEnforcement::AuthTokenMatches(const AuthorizationSet& auth_set, 441 const AuthorizationSet& operation_params, 442 const uint64_t user_secure_id, 443 const int auth_type_index, const int auth_timeout_index, 444 const keymaster_operation_handle_t op_handle, 445 bool is_begin_operation) const { 446 assert(auth_type_index < static_cast<int>(auth_set.size())); 447 assert(auth_timeout_index < static_cast<int>(auth_set.size())); 448 449 keymaster_blob_t auth_token_blob; 450 if (!operation_params.GetTagValue(TAG_AUTH_TOKEN, &auth_token_blob)) { 451 LOG_E("Authentication required, but auth token not provided", 0); 452 return false; 453 } 454 455 if (auth_token_blob.data_length != sizeof(hw_auth_token_t)) { 456 LOG_E("Bug: Auth token is the wrong size (%d expected, %d found)", sizeof(hw_auth_token_t), 457 auth_token_blob.data_length); 458 return false; 459 } 460 461 hw_auth_token_t auth_token; 462 memcpy(&auth_token, auth_token_blob.data, sizeof(hw_auth_token_t)); 463 if (auth_token.version != HW_AUTH_TOKEN_VERSION) { 464 LOG_E("Bug: Auth token is the version %d (or is not an auth token). Expected %d", 465 auth_token.version, HW_AUTH_TOKEN_VERSION); 466 return false; 467 } 468 469 if (!ValidateTokenSignature(auth_token)) { 470 LOG_E("Auth token signature invalid", 0); 471 return false; 472 } 473 474 if (auth_timeout_index == -1 && op_handle && op_handle != auth_token.challenge) { 475 LOG_E("Auth token has the challenge %llu, need %llu", auth_token.challenge, op_handle); 476 return false; 477 } 478 479 if (user_secure_id != auth_token.user_id && user_secure_id != auth_token.authenticator_id) { 480 LOG_I("Auth token SIDs %llu and %llu do not match key SID %llu", auth_token.user_id, 481 auth_token.authenticator_id, user_secure_id); 482 return false; 483 } 484 485 if (auth_type_index < 0 || auth_type_index > static_cast<int>(auth_set.size())) { 486 LOG_E("Auth required but no auth type found", 0); 487 return false; 488 } 489 490 assert(auth_set[auth_type_index].tag == KM_TAG_USER_AUTH_TYPE); 491 if (auth_set[auth_type_index].tag != KM_TAG_USER_AUTH_TYPE) 492 return false; 493 494 uint32_t key_auth_type_mask = auth_set[auth_type_index].integer; 495 uint32_t token_auth_type = ntoh(auth_token.authenticator_type); 496 if ((key_auth_type_mask & token_auth_type) == 0) { 497 LOG_E("Key requires match of auth type mask 0%uo, but token contained 0%uo", 498 key_auth_type_mask, token_auth_type); 499 return false; 500 } 501 502 if (auth_timeout_index != -1 && is_begin_operation) { 503 assert(auth_set[auth_timeout_index].tag == KM_TAG_AUTH_TIMEOUT); 504 if (auth_set[auth_timeout_index].tag != KM_TAG_AUTH_TIMEOUT) 505 return false; 506 507 if (auth_token_timed_out(auth_token, auth_set[auth_timeout_index].integer)) { 508 LOG_E("Auth token has timed out", 0); 509 return false; 510 } 511 } 512 513 // Survived the whole gauntlet. We have authentage! 514 return true; 515 } 516 517 bool AccessTimeMap::LastKeyAccessTime(km_id_t keyid, uint32_t* last_access_time) const { 518 for (auto& entry : last_access_list_) 519 if (entry.keyid == keyid) { 520 *last_access_time = entry.access_time; 521 return true; 522 } 523 return false; 524 } 525 526 bool AccessTimeMap::UpdateKeyAccessTime(km_id_t keyid, uint32_t current_time, uint32_t timeout) { 527 List<AccessTime>::iterator iter; 528 for (iter = last_access_list_.begin(); iter != last_access_list_.end();) { 529 if (iter->keyid == keyid) { 530 iter->access_time = current_time; 531 return true; 532 } 533 534 // Expire entry if possible. 535 assert(current_time >= iter->access_time); 536 if (current_time - iter->access_time >= iter->timeout) 537 iter = last_access_list_.erase(iter); 538 else 539 ++iter; 540 } 541 542 if (last_access_list_.size() >= max_size_) 543 return false; 544 545 AccessTime new_entry; 546 new_entry.keyid = keyid; 547 new_entry.access_time = current_time; 548 new_entry.timeout = timeout; 549 last_access_list_.push_front(new_entry); 550 return true; 551 } 552 553 bool AccessCountMap::KeyAccessCount(km_id_t keyid, uint32_t* count) const { 554 for (auto& entry : access_count_list_) 555 if (entry.keyid == keyid) { 556 *count = entry.access_count; 557 return true; 558 } 559 return false; 560 } 561 562 bool AccessCountMap::IncrementKeyAccessCount(km_id_t keyid) { 563 for (auto& entry : access_count_list_) 564 if (entry.keyid == keyid) { 565 // Note that the 'if' below will always be true because KM_TAG_MAX_USES_PER_BOOT is a 566 // uint32_t, and as soon as entry.access_count reaches the specified maximum value 567 // operation requests will be rejected and access_count won't be incremented any more. 568 // And, besides, UINT64_MAX is huge. But we ensure that it doesn't wrap anyway, out of 569 // an abundance of caution. 570 if (entry.access_count < UINT64_MAX) 571 ++entry.access_count; 572 return true; 573 } 574 575 if (access_count_list_.size() >= max_size_) 576 return false; 577 578 AccessCount new_entry; 579 new_entry.keyid = keyid; 580 new_entry.access_count = 1; 581 access_count_list_.push_front(new_entry); 582 return true; 583 } 584 }; /* namespace keymaster */ 585
