2 * Copyright (C) 2014 The Android Open Source Project
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
17 #define _LARGEFILE64_SOURCE
25 #include <sys/types.h>
30 #include <openssl/asn1.h>
31 #include <openssl/asn1t.h>
32 #include <openssl/crypto.h>
33 #include <openssl/err.h>
34 #include <openssl/evp.h>
35 #include <openssl/pem.h>
36 #include <openssl/rsa.h>
37 #include <openssl/x509.h>
41 #define FORMAT_VERSION 1
42 #define BUFFER_SIZE (1024 * 1024)
49 ASN1_SEQUENCE(AuthAttrs) = {
50 ASN1_SIMPLE(AuthAttrs, target, ASN1_PRINTABLE),
51 ASN1_SIMPLE(AuthAttrs, length, ASN1_INTEGER)
52 } ASN1_SEQUENCE_END(AuthAttrs)
54 IMPLEMENT_ASN1_FUNCTIONS(AuthAttrs)
57 ASN1_INTEGER *formatVersion;
59 X509_ALGOR *algorithmIdentifier;
60 AuthAttrs *authenticatedAttributes;
61 ASN1_OCTET_STRING *signature;
64 ASN1_SEQUENCE(BootSignature) = {
65 ASN1_SIMPLE(BootSignature, formatVersion, ASN1_INTEGER),
66 ASN1_SIMPLE(BootSignature, certificate, X509),
67 ASN1_SIMPLE(BootSignature, algorithmIdentifier, X509_ALGOR),
68 ASN1_SIMPLE(BootSignature, authenticatedAttributes, AuthAttrs),
69 ASN1_SIMPLE(BootSignature, signature, ASN1_OCTET_STRING)
70 } ASN1_SEQUENCE_END(BootSignature)
72 IMPLEMENT_ASN1_FUNCTIONS(BootSignature)
74 static BIO *g_error = NULL;
77 * Rounds n up to the nearest multiple of page_size
78 * @param n The value to round
79 * @param page_size Page size
81 static uint64_t page_align(uint64_t n, uint64_t page_size)
83 return (((n + page_size - 1) / page_size) * page_size);
87 * Calculates the offset to the beginning of the BootSignature block
88 * based on the boot image header. The signature will start after the
89 * the boot image contents.
90 * @param fd File descriptor to the boot image
91 * @param offset Receives the offset in bytes
93 static int get_signature_offset(int fd, off64_t *offset)
96 struct boot_img_hdr hdr;
102 if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) {
106 if (memcmp(BOOT_MAGIC, hdr.magic, BOOT_MAGIC_SIZE) != 0) {
107 printf("Invalid boot image: missing magic\n");
111 if (!hdr.page_size) {
112 printf("Invalid boot image: page size must be non-zero\n");
116 *offset = page_align(hdr.page_size
117 + page_align(hdr.kernel_size, hdr.page_size)
118 + page_align(hdr.ramdisk_size, hdr.page_size)
119 + page_align(hdr.second_size, hdr.page_size),
126 * Reads and parses the ASN.1 BootSignature block from the given offset
127 * @param fd File descriptor to the boot image
128 * @param offset Offset from the beginning of file to the signature
129 * @param bs Pointer to receive the BootImage structure
131 static int read_signature(int fd, off64_t offset, BootSignature **bs)
139 if (lseek64(fd, offset, SEEK_SET) == -1) {
143 if ((in = BIO_new_fd(fd, BIO_NOCLOSE)) == NULL) {
144 ERR_print_errors(g_error);
148 if ((*bs = ASN1_item_d2i_bio(ASN1_ITEM_rptr(BootSignature), in, bs)) == NULL) {
149 ERR_print_errors(g_error);
159 * Validates the format of the boot signature block, and checks that
160 * the length in authenticated attributes matches the actual length of
162 * @param bs The boot signature block to validate
163 * @param length The actual length of the boot image without the signature
165 static int validate_signature_block(const BootSignature *bs, uint64_t length)
178 /* Confirm that formatVersion matches our supported version */
179 if (!BN_set_word(&expected, FORMAT_VERSION)) {
180 ERR_print_errors(g_error);
184 ASN1_INTEGER_to_BN(bs->formatVersion, &value);
186 if (BN_cmp(&expected, &value) != 0) {
187 printf("Unsupported signature version\n");
194 /* Confirm that the length of the image matches with the length in
195 the authenticated attributes */
196 length = htobe64(length);
197 BN_bin2bn((const unsigned char *) &length, sizeof(length), &expected);
199 ASN1_INTEGER_to_BN(bs->authenticatedAttributes->length, &value);
201 if (BN_cmp(&expected, &value) != 0) {
202 printf("Image length doesn't match signature attributes\n");
216 * Creates a SHA-256 hash from the boot image contents and the encoded
217 * authenticated attributes.
218 * @param fd File descriptor to the boot image
219 * @param length Length of the boot image without the signature block
220 * @param aa Pointer to AuthAttrs
221 * @param digest Pointer to a buffer where the hash is written
223 static int hash_image(int fd, uint64_t length, const AuthAttrs *aa,
224 unsigned char *digest)
226 EVP_MD_CTX *ctx = NULL;
230 unsigned char *attrs = NULL;
231 unsigned char *buffer = NULL;
232 unsigned char *p = NULL;
235 if (!aa || !digest) {
239 if ((buffer = malloc(BUFFER_SIZE)) == NULL) {
243 if (lseek64(fd, 0, SEEK_SET) != 0) {
247 if ((ctx = EVP_MD_CTX_create()) == NULL) {
248 ERR_print_errors(g_error);
252 EVP_DigestInit(ctx, EVP_sha256());
257 if ((length - total) < BUFFER_SIZE) {
258 bytes = length - total;
261 if ((bytes = read(fd, buffer, bytes)) == -1) {
262 printf("%s\n", strerror(errno));
266 EVP_DigestUpdate(ctx, buffer, bytes);
268 } while (total < length);
270 if ((bytes = i2d_AuthAttrs((AuthAttrs *) aa, NULL)) < 0) {
271 ERR_print_errors(g_error);
275 if ((attrs = OPENSSL_malloc(bytes)) == NULL) {
276 ERR_print_errors(g_error);
282 if (i2d_AuthAttrs((AuthAttrs *) aa, &p) < 0) {
283 ERR_print_errors(g_error);
287 EVP_DigestUpdate(ctx, attrs, bytes);
288 EVP_DigestFinal(ctx, digest, NULL);
298 EVP_MD_CTX_destroy(ctx);
309 * Verifies the RSA signature against the pubkey (certificate) in the
310 * BootSignature, and additionally against the pubkey file if provided.
311 * @param fd File descriptor to the boot image
312 * @param length Length of the boot image without the signature block
313 * @param bs The boot signature block
314 * @param pkey The external pubkey file
316 static int verify_signature(int fd, uint64_t length, const BootSignature *bs,
320 EVP_PKEY *pkey_bs = NULL;
322 RSA *rsa_pkey = NULL;
323 BIO *bio_pkey = NULL;
324 unsigned char digest[SHA256_DIGEST_LENGTH];
330 if (hash_image(fd, length, bs->authenticatedAttributes, digest) == -1) {
334 if ((pkey_bs = X509_get_pubkey(bs->certificate)) == NULL) {
335 ERR_print_errors(g_error);
339 if ((rsa_bs = EVP_PKEY_get1_RSA(pkey_bs)) == NULL) {
340 ERR_print_errors(g_error);
344 if (!RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH,
345 bs->signature->data, bs->signature->length, rsa_bs)) {
346 ERR_print_errors(g_error);
351 if ((bio_pkey = BIO_new_file(pkey, "r")) == NULL) {
352 ERR_print_errors(g_error);
356 if ((rsa_pkey = PEM_read_bio_RSA_PUBKEY(bio_pkey, NULL, NULL, NULL)) == NULL) {
357 ERR_print_errors(g_error);
361 if (!RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH,
362 bs->signature->data, bs->signature->length, rsa_pkey)) {
363 ERR_print_errors(g_error);
372 EVP_PKEY_free(pkey_bs);
380 BIO_free_all(bio_pkey);
391 * Given the file name of a signed boot image, verifies the signature
392 * @param image_file Name of the boot image file
394 static int verify(const char *image_file, const char *pkey)
396 BootSignature *bs = NULL;
405 if ((fd = open(image_file, O_RDONLY | O_LARGEFILE)) == -1) {
409 if (get_signature_offset(fd, &offset) == -1) {
413 if (read_signature(fd, offset, &bs) == -1) {
417 if (validate_signature_block(bs, offset) == -1) {
421 if (verify_signature(fd, offset, bs, pkey) == -1) {
425 printf("Signature is VALID\n");
430 BootSignature_free(bs);
442 printf("Usage: verify_boot_signature <path-to-boot-image>\n"
443 " verify_boot_signature <path-to-boot-image> <pubkey>\n");
446 int main(int argc, char *argv[])
448 if (argc != 2 && argc != 3) {
453 /* BIO descriptor for logging OpenSSL errors to stderr */
454 if ((g_error = BIO_new_fd(STDERR_FILENO, BIO_NOCLOSE)) == NULL) {
455 printf("Failed to allocate a BIO handle for error output\n");
459 ERR_load_crypto_strings();
461 const char *pkey = (argc == 2) ? NULL : argv[2];
463 return verify(argv[1], pkey);