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
24 #include <sys/types.h>
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>
37 #define FORMAT_VERSION 1
38 #define BUFFER_SIZE (1024 * 1024)
45 ASN1_SEQUENCE(AuthAttrs) = {
46 ASN1_SIMPLE(AuthAttrs, target, ASN1_PRINTABLE),
47 ASN1_SIMPLE(AuthAttrs, length, ASN1_INTEGER)
48 } ASN1_SEQUENCE_END(AuthAttrs)
50 IMPLEMENT_ASN1_FUNCTIONS(AuthAttrs)
53 ASN1_INTEGER *formatVersion;
55 X509_ALGOR *algorithmIdentifier;
56 AuthAttrs *authenticatedAttributes;
57 ASN1_OCTET_STRING *signature;
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)
68 IMPLEMENT_ASN1_FUNCTIONS(BootSignature)
70 static BIO *g_error = NULL;
73 * Rounds n up to the nearest multiple of page_size
74 * @param n The value to round
75 * @param page_size Page size
77 static uint64_t page_align(uint64_t n, uint64_t page_size)
79 return (((n + page_size - 1) / page_size) * page_size);
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
89 static int get_signature_offset(int fd, off64_t *offset)
92 struct boot_img_hdr hdr;
98 if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) {
102 if (memcmp(BOOT_MAGIC, hdr.magic, BOOT_MAGIC_SIZE) != 0) {
103 printf("Invalid boot image: missing magic\n");
107 if (!hdr.page_size) {
108 printf("Invalid boot image: page size must be non-zero\n");
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),
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
127 static int read_signature(int fd, off64_t offset, BootSignature **bs)
135 if (lseek64(fd, offset, SEEK_SET) == -1) {
139 if ((in = BIO_new_fd(fd, BIO_NOCLOSE)) == NULL) {
140 ERR_print_errors(g_error);
144 if ((*bs = ASN1_item_d2i_bio(ASN1_ITEM_rptr(BootSignature), in, bs)) == NULL) {
145 ERR_print_errors(g_error);
155 * Validates the format of the boot signature block, and checks that
156 * the length in authenticated attributes matches the actual length of
158 * @param bs The boot signature block to validate
159 * @param length The actual length of the boot image without the signature
161 static int validate_signature_block(const BootSignature *bs, uint64_t length)
174 /* Confirm that formatVersion matches our supported version */
175 if (!BN_set_word(&expected, FORMAT_VERSION)) {
176 ERR_print_errors(g_error);
180 ASN1_INTEGER_to_BN(bs->formatVersion, &value);
182 if (BN_cmp(&expected, &value) != 0) {
183 printf("Unsupported signature version\n");
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);
195 ASN1_INTEGER_to_BN(bs->authenticatedAttributes->length, &value);
197 if (BN_cmp(&expected, &value) != 0) {
198 printf("Image length doesn't match signature attributes\n");
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
219 static int hash_image(int fd, uint64_t length, const AuthAttrs *aa,
220 unsigned char *digest)
222 EVP_MD_CTX *ctx = NULL;
226 unsigned char *attrs = NULL;
227 unsigned char *buffer = NULL;
228 unsigned char *p = NULL;
231 if (!aa || !digest) {
235 if ((buffer = malloc(BUFFER_SIZE)) == NULL) {
239 if (lseek64(fd, 0, SEEK_SET) != 0) {
243 if ((ctx = EVP_MD_CTX_create()) == NULL) {
244 ERR_print_errors(g_error);
248 EVP_DigestInit(ctx, EVP_sha256());
253 if ((length - total) < BUFFER_SIZE) {
254 bytes = length - total;
257 if ((bytes = read(fd, buffer, bytes)) == -1) {
258 printf("%s\n", strerror(errno));
262 EVP_DigestUpdate(ctx, buffer, bytes);
264 } while (total < length);
266 if ((bytes = i2d_AuthAttrs((AuthAttrs *) aa, NULL)) < 0) {
267 ERR_print_errors(g_error);
271 if ((attrs = OPENSSL_malloc(bytes)) == NULL) {
272 ERR_print_errors(g_error);
278 if (i2d_AuthAttrs((AuthAttrs *) aa, &p) < 0) {
279 ERR_print_errors(g_error);
283 EVP_DigestUpdate(ctx, attrs, bytes);
284 EVP_DigestFinal(ctx, digest, NULL);
294 EVP_MD_CTX_destroy(ctx);
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
310 static int verify_signature(int fd, uint64_t length, const BootSignature *bs)
313 EVP_PKEY *pkey = NULL;
315 unsigned char digest[SHA256_DIGEST_LENGTH];
321 if (hash_image(fd, length, bs->authenticatedAttributes, digest) == -1) {
325 if ((pkey = X509_get_pubkey(bs->certificate)) == NULL) {
326 ERR_print_errors(g_error);
330 if ((rsa = EVP_PKEY_get1_RSA(pkey)) == NULL) {
331 ERR_print_errors(g_error);
335 if (!RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH,
336 bs->signature->data, bs->signature->length, rsa)) {
337 ERR_print_errors(g_error);
356 * Given the file name of a signed boot image, verifies the signature
357 * @param image_file Name of the boot image file
359 static int verify(const char *image_file)
361 BootSignature *bs = NULL;
370 if ((fd = open(image_file, O_RDONLY | O_LARGEFILE)) == -1) {
374 if (get_signature_offset(fd, &offset) == -1) {
378 if (read_signature(fd, offset, &bs) == -1) {
382 if (validate_signature_block(bs, offset) == -1) {
386 if (verify_signature(fd, offset, bs) == -1) {
390 printf("Signature is VALID\n");
395 BootSignature_free(bs);
407 printf("Usage: verify_boot_signature <path-to-boot-image>\n");
410 int main(int argc, char *argv[])
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");
423 ERR_load_crypto_strings();
425 return verify(argv[1]);