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 #define _LARGEFILE64_SOURCE 18 19 #include <endian.h> 20 #include <stddef.h> 21 #include <stdint.h> 22 #include <string.h> 23 #include <sys/stat.h> 24 #include <sys/types.h> 25 #include <fcntl.h> 26 #include <unistd.h> 27 28 #include <openssl/asn1.h> 29 #include <openssl/asn1t.h> 30 #include <openssl/err.h> 31 #include <openssl/evp.h> 32 #include <openssl/rsa.h> 33 #include <openssl/x509.h> 34 35 #include "bootimg.h" 36 37 #define FORMAT_VERSION 1 38 #define BUFFER_SIZE (1024 * 1024) 39 40 typedef struct { 41 ASN1_STRING *target; 42 ASN1_INTEGER *length; 43 } AuthAttrs; 44 45 ASN1_SEQUENCE(AuthAttrs) = { 46 ASN1_SIMPLE(AuthAttrs, target, ASN1_PRINTABLE), 47 ASN1_SIMPLE(AuthAttrs, length, ASN1_INTEGER) 48 } ASN1_SEQUENCE_END(AuthAttrs) 49 50 IMPLEMENT_ASN1_FUNCTIONS(AuthAttrs) 51 52 typedef struct { 53 ASN1_INTEGER *formatVersion; 54 X509 *certificate; 55 X509_ALGOR *algorithmIdentifier; 56 AuthAttrs *authenticatedAttributes; 57 ASN1_OCTET_STRING *signature; 58 } BootSignature; 59 60 ASN1_SEQUENCE(BootSignature) = { 61 ASN1_SIMPLE(BootSignature, formatVersion, ASN1_INTEGER), 62 ASN1_SIMPLE(BootSignature, certificate, X509), 63 ASN1_SIMPLE(BootSignature, algorithmIdentifier, X509_ALGOR), 64 ASN1_SIMPLE(BootSignature, authenticatedAttributes, AuthAttrs), 65 ASN1_SIMPLE(BootSignature, signature, ASN1_OCTET_STRING) 66 } ASN1_SEQUENCE_END(BootSignature) 67 68 IMPLEMENT_ASN1_FUNCTIONS(BootSignature) 69 70 static BIO *g_error = NULL; 71 72 /** 73 * Rounds n up to the nearest multiple of page_size 74 * @param n The value to round 75 * @param page_size Page size 76 */ 77 static uint64_t page_align(uint64_t n, uint64_t page_size) 78 { 79 return (((n + page_size - 1) / page_size) * page_size); 80 } 81 82 /** 83 * Calculates the offset to the beginning of the BootSignature block 84 * based on the boot image header. The signature will start after the 85 * the boot image contents. 86 * @param fd File descriptor to the boot image 87 * @param offset Receives the offset in bytes 88 */ 89 static int get_signature_offset(int fd, off64_t *offset) 90 { 91 int i; 92 struct boot_img_hdr hdr; 93 94 if (!offset) { 95 return -1; 96 } 97 98 if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) { 99 return -1; 100 } 101 102 if (memcmp(BOOT_MAGIC, hdr.magic, BOOT_MAGIC_SIZE) != 0) { 103 printf("Invalid boot image: missing magic\n"); 104 return -1; 105 } 106 107 if (!hdr.page_size) { 108 printf("Invalid boot image: page size must be non-zero\n"); 109 return -1; 110 } 111 112 *offset = page_align(hdr.page_size 113 + page_align(hdr.kernel_size, hdr.page_size) 114 + page_align(hdr.ramdisk_size, hdr.page_size) 115 + page_align(hdr.second_size, hdr.page_size), 116 hdr.page_size); 117 118 return 0; 119 } 120 121 /** 122 * Reads and parses the ASN.1 BootSignature block from the given offset 123 * @param fd File descriptor to the boot image 124 * @param offset Offset from the beginning of file to the signature 125 * @param bs Pointer to receive the BootImage structure 126 */ 127 static int read_signature(int fd, off64_t offset, BootSignature **bs) 128 { 129 BIO *in = NULL; 130 131 if (!bs) { 132 return -1; 133 } 134 135 if (lseek64(fd, offset, SEEK_SET) == -1) { 136 return -1; 137 } 138 139 if ((in = BIO_new_fd(fd, BIO_NOCLOSE)) == NULL) { 140 ERR_print_errors(g_error); 141 return -1; 142 } 143 144 if ((*bs = ASN1_item_d2i_bio(ASN1_ITEM_rptr(BootSignature), in, bs)) == NULL) { 145 ERR_print_errors(g_error); 146 BIO_free(in); 147 return -1; 148 } 149 150 BIO_free(in); 151 return 0; 152 } 153 154 /** 155 * Validates the format of the boot signature block, and checks that 156 * the length in authenticated attributes matches the actual length of 157 * the image. 158 * @param bs The boot signature block to validate 159 * @param length The actual length of the boot image without the signature 160 */ 161 static int validate_signature_block(const BootSignature *bs, uint64_t length) 162 { 163 BIGNUM expected; 164 BIGNUM value; 165 int rc = -1; 166 167 if (!bs) { 168 return -1; 169 } 170 171 BN_init(&expected); 172 BN_init(&value); 173 174 /* Confirm that formatVersion matches our supported version */ 175 if (!BN_set_word(&expected, FORMAT_VERSION)) { 176 ERR_print_errors(g_error); 177 goto vsb_done; 178 } 179 180 ASN1_INTEGER_to_BN(bs->formatVersion, &value); 181 182 if (BN_cmp(&expected, &value) != 0) { 183 printf("Unsupported signature version\n"); 184 goto vsb_done; 185 } 186 187 BN_clear(&expected); 188 BN_clear(&value); 189 190 /* Confirm that the length of the image matches with the length in 191 the authenticated attributes */ 192 length = htobe64(length); 193 BN_bin2bn((const unsigned char *) &length, sizeof(length), &expected); 194 195 ASN1_INTEGER_to_BN(bs->authenticatedAttributes->length, &value); 196 197 if (BN_cmp(&expected, &value) != 0) { 198 printf("Image length doesn't match signature attributes\n"); 199 goto vsb_done; 200 } 201 202 rc = 0; 203 204 vsb_done: 205 BN_free(&expected); 206 BN_free(&value); 207 208 return rc; 209 } 210 211 /** 212 * Creates a SHA-256 hash from the boot image contents and the encoded 213 * authenticated attributes. 214 * @param fd File descriptor to the boot image 215 * @param length Length of the boot image without the signature block 216 * @param aa Pointer to AuthAttrs 217 * @param digest Pointer to a buffer where the hash is written 218 */ 219 static int hash_image(int fd, uint64_t length, const AuthAttrs *aa, 220 unsigned char *digest) 221 { 222 EVP_MD_CTX *ctx = NULL; 223 int rc = -1; 224 225 ssize_t bytes = 0; 226 unsigned char *attrs = NULL; 227 unsigned char *buffer = NULL; 228 unsigned char *p = NULL; 229 uint64_t total = 0; 230 231 if (!aa || !digest) { 232 goto hi_done; 233 } 234 235 if ((buffer = malloc(BUFFER_SIZE)) == NULL) { 236 goto hi_done; 237 } 238 239 if (lseek64(fd, 0, SEEK_SET) != 0) { 240 goto hi_done; 241 } 242 243 if ((ctx = EVP_MD_CTX_create()) == NULL) { 244 ERR_print_errors(g_error); 245 goto hi_done; 246 } 247 248 EVP_DigestInit(ctx, EVP_sha256()); 249 250 do { 251 bytes = BUFFER_SIZE; 252 253 if ((length - total) < BUFFER_SIZE) { 254 bytes = length - total; 255 } 256 257 if ((bytes = read(fd, buffer, bytes)) == -1) { 258 printf("%s\n", strerror(errno)); 259 goto hi_done; 260 } 261 262 EVP_DigestUpdate(ctx, buffer, bytes); 263 total += bytes; 264 } while (total < length); 265 266 if ((bytes = i2d_AuthAttrs((AuthAttrs *) aa, NULL)) < 0) { 267 ERR_print_errors(g_error); 268 goto hi_done; 269 } 270 271 if ((attrs = OPENSSL_malloc(bytes)) == NULL) { 272 ERR_print_errors(g_error); 273 goto hi_done; 274 } 275 276 p = attrs; 277 278 if (i2d_AuthAttrs((AuthAttrs *) aa, &p) < 0) { 279 ERR_print_errors(g_error); 280 goto hi_done; 281 } 282 283 EVP_DigestUpdate(ctx, attrs, bytes); 284 EVP_DigestFinal(ctx, digest, NULL); 285 286 rc = 0; 287 288 hi_done: 289 if (buffer) { 290 free(buffer); 291 } 292 293 if (ctx) { 294 EVP_MD_CTX_destroy(ctx); 295 } 296 297 if (attrs) { 298 OPENSSL_free(attrs); 299 } 300 301 return rc; 302 } 303 304 /** 305 * Verifies the RSA signature 306 * @param fd File descriptor to the boot image 307 * @param length Length of the boot image without the signature block 308 * @param bs The boot signature block 309 */ 310 static int verify_signature(int fd, uint64_t length, const BootSignature *bs) 311 { 312 int rc = -1; 313 EVP_PKEY *pkey = NULL; 314 RSA *rsa = NULL; 315 unsigned char digest[SHA256_DIGEST_LENGTH]; 316 317 if (!bs) { 318 goto vs_done; 319 } 320 321 if (hash_image(fd, length, bs->authenticatedAttributes, digest) == -1) { 322 goto vs_done; 323 } 324 325 if ((pkey = X509_get_pubkey(bs->certificate)) == NULL) { 326 ERR_print_errors(g_error); 327 goto vs_done; 328 } 329 330 if ((rsa = EVP_PKEY_get1_RSA(pkey)) == NULL) { 331 ERR_print_errors(g_error); 332 goto vs_done; 333 } 334 335 if (!RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH, 336 bs->signature->data, bs->signature->length, rsa)) { 337 ERR_print_errors(g_error); 338 goto vs_done; 339 } 340 341 rc = 0; 342 343 vs_done: 344 if (pkey) { 345 EVP_PKEY_free(pkey); 346 } 347 348 if (rsa) { 349 RSA_free(rsa); 350 } 351 352 return rc; 353 } 354 355 /** 356 * Given the file name of a signed boot image, verifies the signature 357 * @param image_file Name of the boot image file 358 */ 359 static int verify(const char *image_file) 360 { 361 BootSignature *bs = NULL; 362 int fd = -1; 363 int rc = 1; 364 off64_t offset = 0; 365 366 if (!image_file) { 367 return rc; 368 } 369 370 if ((fd = open(image_file, O_RDONLY | O_LARGEFILE)) == -1) { 371 return rc; 372 } 373 374 if (get_signature_offset(fd, &offset) == -1) { 375 goto out; 376 } 377 378 if (read_signature(fd, offset, &bs) == -1) { 379 goto out; 380 } 381 382 if (validate_signature_block(bs, offset) == -1) { 383 goto out; 384 } 385 386 if (verify_signature(fd, offset, bs) == -1) { 387 goto out; 388 } 389 390 printf("Signature is VALID\n"); 391 rc = 0; 392 393 out: 394 if (bs) { 395 BootSignature_free(bs); 396 } 397 398 if (fd != -1) { 399 close(fd); 400 } 401 402 return rc; 403 } 404 405 static void usage() 406 { 407 printf("Usage: verify_boot_signature <path-to-boot-image>\n"); 408 } 409 410 int main(int argc, char *argv[]) 411 { 412 if (argc != 2) { 413 usage(); 414 return 1; 415 } 416 417 /* BIO descriptor for logging OpenSSL errors to stderr */ 418 if ((g_error = BIO_new_fd(STDERR_FILENO, BIO_NOCLOSE)) == NULL) { 419 printf("Failed to allocate a BIO handle for error output\n"); 420 return 1; 421 } 422 423 ERR_load_crypto_strings(); 424 425 return verify(argv[1]); 426 } 427
