1 /* 2 * Copyright (c) 2015-2022, ARM Limited and Contributors. All rights reserved. 3 * 4 * SPDX-License-Identifier: BSD-3-Clause 5 */ 6 7 /* 8 * X509 parser based on mbed TLS 9 * 10 * This module implements functions to check the integrity of a X509v3 11 * certificate ASN.1 structure and extract authentication parameters from the 12 * extensions field, such as an image hash or a public key. 13 */ 14 15 #include <assert.h> 16 #include <stddef.h> 17 #include <stdint.h> 18 #include <string.h> 19 20 /* mbed TLS headers */ 21 #include <mbedtls/asn1.h> 22 #include <mbedtls/oid.h> 23 #include <mbedtls/platform.h> 24 25 #include <arch_helpers.h> 26 #include <drivers/auth/img_parser_mod.h> 27 #include <drivers/auth/mbedtls/mbedtls_common.h> 28 #include <lib/utils.h> 29 30 /* Maximum OID string length ("a.b.c.d.e.f ...") */ 31 #define MAX_OID_STR_LEN 64 32 33 #define LIB_NAME "mbed TLS X509v3" 34 35 /* Temporary variables to speed up the authentication parameters search. These 36 * variables are assigned once during the integrity check and used any time an 37 * authentication parameter is requested, so we do not have to parse the image 38 * again */ 39 static mbedtls_asn1_buf tbs; 40 static mbedtls_asn1_buf v3_ext; 41 static mbedtls_asn1_buf pk; 42 static mbedtls_asn1_buf sig_alg; 43 static mbedtls_asn1_buf signature; 44 45 /* 46 * Clear all static temporary variables. 47 */ 48 static void clear_temp_vars(void) 49 { 50 #define ZERO_AND_CLEAN(x) \ 51 do { \ 52 zeromem(&x, sizeof(x)); \ 53 clean_dcache_range((uintptr_t)&x, sizeof(x)); \ 54 } while (0); 55 56 ZERO_AND_CLEAN(tbs) 57 ZERO_AND_CLEAN(v3_ext); 58 ZERO_AND_CLEAN(pk); 59 ZERO_AND_CLEAN(sig_alg); 60 ZERO_AND_CLEAN(signature); 61 62 #undef ZERO_AND_CLEAN 63 } 64 65 /* 66 * Get X509v3 extension 67 * 68 * Global variable 'v3_ext' must point to the extensions region 69 * in the certificate. No need to check for errors since the image has passed 70 * the integrity check. 71 */ 72 static int get_ext(const char *oid, void **ext, unsigned int *ext_len) 73 { 74 int oid_len; 75 size_t len; 76 unsigned char *end_ext_data, *end_ext_octet; 77 unsigned char *p; 78 const unsigned char *end; 79 char oid_str[MAX_OID_STR_LEN]; 80 mbedtls_asn1_buf extn_oid; 81 int is_critical; 82 83 assert(oid != NULL); 84 85 p = v3_ext.p; 86 end = v3_ext.p + v3_ext.len; 87 88 mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 89 MBEDTLS_ASN1_SEQUENCE); 90 91 while (p < end) { 92 zeromem(&extn_oid, sizeof(extn_oid)); 93 is_critical = 0; /* DEFAULT FALSE */ 94 95 mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 96 MBEDTLS_ASN1_SEQUENCE); 97 end_ext_data = p + len; 98 99 /* Get extension ID */ 100 extn_oid.tag = *p; 101 mbedtls_asn1_get_tag(&p, end, &extn_oid.len, MBEDTLS_ASN1_OID); 102 extn_oid.p = p; 103 p += extn_oid.len; 104 105 /* Get optional critical */ 106 mbedtls_asn1_get_bool(&p, end_ext_data, &is_critical); 107 108 /* Extension data */ 109 mbedtls_asn1_get_tag(&p, end_ext_data, &len, 110 MBEDTLS_ASN1_OCTET_STRING); 111 end_ext_octet = p + len; 112 113 /* Detect requested extension */ 114 oid_len = mbedtls_oid_get_numeric_string(oid_str, 115 MAX_OID_STR_LEN, 116 &extn_oid); 117 if ((oid_len == MBEDTLS_ERR_OID_BUF_TOO_SMALL) || (oid_len < 0)) { 118 return IMG_PARSER_ERR; 119 } 120 if (((size_t)oid_len == strlen(oid_str)) && !strcmp(oid, oid_str)) { 121 *ext = (void *)p; 122 *ext_len = (unsigned int)len; 123 return IMG_PARSER_OK; 124 } 125 126 /* Next */ 127 p = end_ext_octet; 128 } 129 130 return IMG_PARSER_ERR_NOT_FOUND; 131 } 132 133 134 /* 135 * Check the integrity of the certificate ASN.1 structure. 136 * 137 * Extract the relevant data that will be used later during authentication. 138 * 139 * This function doesn't clear the static variables located on the top of this 140 * file in case of an error. It is only called from check_integrity(), which 141 * performs the cleanup if necessary. 142 */ 143 static int cert_parse(void *img, unsigned int img_len) 144 { 145 int ret, is_critical; 146 size_t len; 147 unsigned char *p, *end, *crt_end, *pk_end; 148 mbedtls_asn1_buf sig_alg1, sig_alg2; 149 /* 150 * The unique ASN.1 DER encoding of [0] EXPLICIT INTEGER { v3(2} }. 151 */ 152 static const char v3[] = { 153 /* The outer CONTEXT SPECIFIC 0 tag */ 154 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC | 0, 155 /* The number bytes used to encode the inner INTEGER */ 156 3, 157 /* The tag of the inner INTEGER */ 158 MBEDTLS_ASN1_INTEGER, 159 /* The number of bytes needed to represent 2 */ 160 1, 161 /* The actual value 2 */ 162 2, 163 }; 164 165 p = (unsigned char *)img; 166 len = img_len; 167 end = p + len; 168 169 /* 170 * Certificate ::= SEQUENCE { 171 * tbsCertificate TBSCertificate, 172 * signatureAlgorithm AlgorithmIdentifier, 173 * signatureValue BIT STRING } 174 */ 175 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 176 MBEDTLS_ASN1_SEQUENCE); 177 if (ret != 0) { 178 return IMG_PARSER_ERR_FORMAT; 179 } 180 181 if (len != (size_t)(end - p)) { 182 return IMG_PARSER_ERR_FORMAT; 183 } 184 crt_end = p + len; 185 186 /* 187 * TBSCertificate ::= SEQUENCE { 188 */ 189 tbs.p = p; 190 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 191 MBEDTLS_ASN1_SEQUENCE); 192 if (ret != 0) { 193 return IMG_PARSER_ERR_FORMAT; 194 } 195 end = p + len; 196 tbs.len = end - tbs.p; 197 198 /* 199 * Version ::= [0] EXPLICIT INTEGER { v1(0), v2(1), v3(2) } 200 * -- only v3 accepted 201 */ 202 if (((end - p) <= (ptrdiff_t)sizeof(v3)) || 203 (memcmp(p, v3, sizeof(v3)) != 0)) { 204 return IMG_PARSER_ERR_FORMAT; 205 } 206 p += sizeof(v3); 207 208 /* 209 * CertificateSerialNumber ::= INTEGER 210 */ 211 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_INTEGER); 212 if (ret != 0) { 213 return IMG_PARSER_ERR_FORMAT; 214 } 215 p += len; 216 217 /* 218 * signature AlgorithmIdentifier 219 */ 220 sig_alg1.p = p; 221 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 222 MBEDTLS_ASN1_SEQUENCE); 223 if (ret != 0) { 224 return IMG_PARSER_ERR_FORMAT; 225 } 226 if ((end - p) < 1) { 227 return IMG_PARSER_ERR_FORMAT; 228 } 229 sig_alg1.len = (p + len) - sig_alg1.p; 230 p += len; 231 232 /* 233 * issuer Name 234 */ 235 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 236 MBEDTLS_ASN1_SEQUENCE); 237 if (ret != 0) { 238 return IMG_PARSER_ERR_FORMAT; 239 } 240 p += len; 241 242 /* 243 * Validity ::= SEQUENCE { 244 * notBefore Time, 245 * notAfter Time } 246 * 247 */ 248 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 249 MBEDTLS_ASN1_SEQUENCE); 250 if (ret != 0) { 251 return IMG_PARSER_ERR_FORMAT; 252 } 253 p += len; 254 255 /* 256 * subject Name 257 */ 258 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 259 MBEDTLS_ASN1_SEQUENCE); 260 if (ret != 0) { 261 return IMG_PARSER_ERR_FORMAT; 262 } 263 p += len; 264 265 /* 266 * SubjectPublicKeyInfo 267 */ 268 pk.p = p; 269 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 270 MBEDTLS_ASN1_SEQUENCE); 271 if (ret != 0) { 272 return IMG_PARSER_ERR_FORMAT; 273 } 274 pk_end = p + len; 275 pk.len = pk_end - pk.p; 276 277 ret = mbedtls_asn1_get_tag(&p, pk_end, &len, MBEDTLS_ASN1_CONSTRUCTED | 278 MBEDTLS_ASN1_SEQUENCE); 279 if (ret != 0) { 280 return IMG_PARSER_ERR_FORMAT; 281 } 282 p += len; 283 284 /* Key is a BIT STRING and must use all bytes in SubjectPublicKeyInfo */ 285 ret = mbedtls_asn1_get_bitstring_null(&p, pk_end, &len); 286 if ((ret != 0) || (p + len != pk_end)) { 287 return IMG_PARSER_ERR_FORMAT; 288 } 289 p = pk_end; 290 291 /* 292 * issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL, 293 */ 294 ret = mbedtls_asn1_get_tag(&p, end, &len, 295 MBEDTLS_ASN1_CONTEXT_SPECIFIC | 296 MBEDTLS_ASN1_CONSTRUCTED | 1); 297 if (ret != 0) { 298 if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) { 299 return IMG_PARSER_ERR_FORMAT; 300 } 301 } else { 302 p += len; 303 } 304 305 /* 306 * subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL, 307 */ 308 ret = mbedtls_asn1_get_tag(&p, end, &len, 309 MBEDTLS_ASN1_CONTEXT_SPECIFIC | 310 MBEDTLS_ASN1_CONSTRUCTED | 2); 311 if (ret != 0) { 312 if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) { 313 return IMG_PARSER_ERR_FORMAT; 314 } 315 } else { 316 p += len; 317 } 318 319 /* 320 * extensions [3] EXPLICIT Extensions OPTIONAL 321 * } 322 * 323 * X.509 and RFC5280 allow omitting the extensions entirely. 324 * However, in TF-A, a certificate with no extensions would 325 * always fail later on, as the extensions contain the 326 * information needed to authenticate the next stage in the 327 * boot chain. Furthermore, get_ext() assumes that the 328 * extensions have been parsed into v3_ext, and allowing 329 * there to be no extensions would pointlessly complicate 330 * the code. Therefore, just reject certificates without 331 * extensions. This is also why version 1 and 2 certificates 332 * are rejected above. 333 */ 334 ret = mbedtls_asn1_get_tag(&p, end, &len, 335 MBEDTLS_ASN1_CONTEXT_SPECIFIC | 336 MBEDTLS_ASN1_CONSTRUCTED | 3); 337 if ((ret != 0) || (len != (size_t)(end - p))) { 338 return IMG_PARSER_ERR_FORMAT; 339 } 340 341 /* 342 * Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension 343 * -- must use all remaining bytes in TBSCertificate 344 */ 345 v3_ext.p = p; 346 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 347 MBEDTLS_ASN1_SEQUENCE); 348 if ((ret != 0) || (len != (size_t)(end - p))) { 349 return IMG_PARSER_ERR_FORMAT; 350 } 351 v3_ext.len = end - v3_ext.p; 352 353 /* 354 * Check extensions integrity. At least one extension is 355 * required: the ASN.1 specifies a minimum size of 1, and at 356 * least one extension is needed to authenticate the next stage 357 * in the boot chain. 358 */ 359 do { 360 ret = mbedtls_asn1_get_tag(&p, end, &len, 361 MBEDTLS_ASN1_CONSTRUCTED | 362 MBEDTLS_ASN1_SEQUENCE); 363 if (ret != 0) { 364 return IMG_PARSER_ERR_FORMAT; 365 } 366 367 /* Get extension ID */ 368 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_OID); 369 if (ret != 0) { 370 return IMG_PARSER_ERR_FORMAT; 371 } 372 p += len; 373 374 /* Get optional critical */ 375 ret = mbedtls_asn1_get_bool(&p, end, &is_critical); 376 if ((ret != 0) && (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)) { 377 return IMG_PARSER_ERR_FORMAT; 378 } 379 380 /* Data should be octet string type */ 381 ret = mbedtls_asn1_get_tag(&p, end, &len, 382 MBEDTLS_ASN1_OCTET_STRING); 383 if (ret != 0) { 384 return IMG_PARSER_ERR_FORMAT; 385 } 386 p += len; 387 } while (p < end); 388 389 if (p != end) { 390 return IMG_PARSER_ERR_FORMAT; 391 } 392 393 end = crt_end; 394 395 /* 396 * } 397 * -- end of TBSCertificate 398 * 399 * signatureAlgorithm AlgorithmIdentifier 400 */ 401 sig_alg2.p = p; 402 ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED | 403 MBEDTLS_ASN1_SEQUENCE); 404 if (ret != 0) { 405 return IMG_PARSER_ERR_FORMAT; 406 } 407 if ((end - p) < 1) { 408 return IMG_PARSER_ERR_FORMAT; 409 } 410 sig_alg2.len = (p + len) - sig_alg2.p; 411 p += len; 412 413 /* Compare both signature algorithms */ 414 if (sig_alg1.len != sig_alg2.len) { 415 return IMG_PARSER_ERR_FORMAT; 416 } 417 if (0 != memcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) { 418 return IMG_PARSER_ERR_FORMAT; 419 } 420 memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg)); 421 422 /* 423 * signatureValue BIT STRING 424 */ 425 signature.p = p; 426 ret = mbedtls_asn1_get_bitstring_null(&p, end, &len); 427 if (ret != 0) { 428 return IMG_PARSER_ERR_FORMAT; 429 } 430 signature.len = (p + len) - signature.p; 431 p += len; 432 433 /* Check certificate length */ 434 if (p != end) { 435 return IMG_PARSER_ERR_FORMAT; 436 } 437 438 return IMG_PARSER_OK; 439 } 440 441 442 /* Exported functions */ 443 444 static void init(void) 445 { 446 mbedtls_init(); 447 } 448 449 /* 450 * Wrapper for cert_parse() that clears the static variables used by it in case 451 * of an error. 452 */ 453 static int check_integrity(void *img, unsigned int img_len) 454 { 455 int rc = cert_parse(img, img_len); 456 457 if (rc != IMG_PARSER_OK) 458 clear_temp_vars(); 459 460 return rc; 461 } 462 463 /* 464 * Extract an authentication parameter from an X509v3 certificate 465 * 466 * This function returns a pointer to the extracted data and its length. 467 * Depending on the type of parameter, a pointer to the data stored in the 468 * certificate may be returned (i.e. an octet string containing a hash). Other 469 * data may need to be copied and formatted (i.e. integers). In the later case, 470 * a buffer of the correct type needs to be statically allocated, filled and 471 * returned. 472 */ 473 static int get_auth_param(const auth_param_type_desc_t *type_desc, 474 void *img, unsigned int img_len, 475 void **param, unsigned int *param_len) 476 { 477 int rc = IMG_PARSER_OK; 478 479 /* We do not use img because the check_integrity function has already 480 * extracted the relevant data (v3_ext, pk, sig_alg, etc) */ 481 482 switch (type_desc->type) { 483 case AUTH_PARAM_RAW_DATA: 484 /* Data to be signed */ 485 *param = (void *)tbs.p; 486 *param_len = (unsigned int)tbs.len; 487 break; 488 case AUTH_PARAM_HASH: 489 case AUTH_PARAM_NV_CTR: 490 /* All these parameters are included as X509v3 extensions */ 491 rc = get_ext(type_desc->cookie, param, param_len); 492 break; 493 case AUTH_PARAM_PUB_KEY: 494 if (type_desc->cookie != 0) { 495 /* Get public key from extension */ 496 rc = get_ext(type_desc->cookie, param, param_len); 497 } else { 498 /* Get the subject public key */ 499 *param = (void *)pk.p; 500 *param_len = (unsigned int)pk.len; 501 } 502 break; 503 case AUTH_PARAM_SIG_ALG: 504 /* Get the certificate signature algorithm */ 505 *param = (void *)sig_alg.p; 506 *param_len = (unsigned int)sig_alg.len; 507 break; 508 case AUTH_PARAM_SIG: 509 /* Get the certificate signature */ 510 *param = (void *)signature.p; 511 *param_len = (unsigned int)signature.len; 512 break; 513 default: 514 rc = IMG_PARSER_ERR_NOT_FOUND; 515 break; 516 } 517 518 return rc; 519 } 520 521 REGISTER_IMG_PARSER_LIB(IMG_CERT, LIB_NAME, init, \ 522 check_integrity, get_auth_param); 523