blob: 58b7a1947b31e9584538dbccec742602f6fed593 [file] [log] [blame]
/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define _LARGEFILE64_SOURCE
#include <endian.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <openssl/asn1.h>
#include <openssl/asn1t.h>
#include <openssl/crypto.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/rsa.h>
#include <openssl/x509.h>
#include "bootimg.h"
#define FORMAT_VERSION 1
#define BUFFER_SIZE (1024 * 1024)
typedef struct {
ASN1_STRING *target;
ASN1_INTEGER *length;
} AuthAttrs;
ASN1_SEQUENCE(AuthAttrs) = {
ASN1_SIMPLE(AuthAttrs, target, ASN1_PRINTABLE),
ASN1_SIMPLE(AuthAttrs, length, ASN1_INTEGER)
} ASN1_SEQUENCE_END(AuthAttrs)
IMPLEMENT_ASN1_FUNCTIONS(AuthAttrs)
typedef struct {
ASN1_INTEGER *formatVersion;
X509 *certificate;
X509_ALGOR *algorithmIdentifier;
AuthAttrs *authenticatedAttributes;
ASN1_OCTET_STRING *signature;
} BootSignature;
ASN1_SEQUENCE(BootSignature) = {
ASN1_SIMPLE(BootSignature, formatVersion, ASN1_INTEGER),
ASN1_SIMPLE(BootSignature, certificate, X509),
ASN1_SIMPLE(BootSignature, algorithmIdentifier, X509_ALGOR),
ASN1_SIMPLE(BootSignature, authenticatedAttributes, AuthAttrs),
ASN1_SIMPLE(BootSignature, signature, ASN1_OCTET_STRING)
} ASN1_SEQUENCE_END(BootSignature)
IMPLEMENT_ASN1_FUNCTIONS(BootSignature)
static BIO *g_error = NULL;
#if defined(OPENSSL_IS_BORINGSSL)
/* In BoringSSL, ERR_print_errors has been moved to the BIO functions in order
* to avoid the incorrect dependency of ERR on BIO. */
static void ERR_print_errors(BIO *bio) {
BIO_print_errors(bio);
}
#endif
/**
* Rounds n up to the nearest multiple of page_size
* @param n The value to round
* @param page_size Page size
*/
static uint64_t page_align(uint64_t n, uint64_t page_size)
{
return (((n + page_size - 1) / page_size) * page_size);
}
/**
* Calculates the offset to the beginning of the BootSignature block
* based on the boot image header. The signature will start after the
* the boot image contents.
* @param fd File descriptor to the boot image
* @param offset Receives the offset in bytes
*/
static int get_signature_offset(int fd, off64_t *offset)
{
int i;
struct boot_img_hdr hdr;
if (!offset) {
return -1;
}
if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) {
return -1;
}
if (memcmp(BOOT_MAGIC, hdr.magic, BOOT_MAGIC_SIZE) != 0) {
printf("Invalid boot image: missing magic\n");
return -1;
}
if (!hdr.page_size) {
printf("Invalid boot image: page size must be non-zero\n");
return -1;
}
*offset = page_align(hdr.page_size
+ page_align(hdr.kernel_size, hdr.page_size)
+ page_align(hdr.ramdisk_size, hdr.page_size)
+ page_align(hdr.second_size, hdr.page_size),
hdr.page_size);
return 0;
}
/**
* Reads and parses the ASN.1 BootSignature block from the given offset
* @param fd File descriptor to the boot image
* @param offset Offset from the beginning of file to the signature
* @param bs Pointer to receive the BootImage structure
*/
static int read_signature(int fd, off64_t offset, BootSignature **bs)
{
BIO *in = NULL;
if (!bs) {
return -1;
}
if (lseek64(fd, offset, SEEK_SET) == -1) {
return -1;
}
if ((in = BIO_new_fd(fd, BIO_NOCLOSE)) == NULL) {
ERR_print_errors(g_error);
return -1;
}
if ((*bs = ASN1_item_d2i_bio(ASN1_ITEM_rptr(BootSignature), in, bs)) == NULL) {
ERR_print_errors(g_error);
BIO_free(in);
return -1;
}
BIO_free(in);
return 0;
}
/**
* Validates the format of the boot signature block, and checks that
* the length in authenticated attributes matches the actual length of
* the image.
* @param bs The boot signature block to validate
* @param length The actual length of the boot image without the signature
*/
static int validate_signature_block(const BootSignature *bs, uint64_t length)
{
BIGNUM expected;
BIGNUM value;
int rc = -1;
if (!bs) {
return -1;
}
BN_init(&expected);
BN_init(&value);
/* Confirm that formatVersion matches our supported version */
if (!BN_set_word(&expected, FORMAT_VERSION)) {
ERR_print_errors(g_error);
goto vsb_done;
}
ASN1_INTEGER_to_BN(bs->formatVersion, &value);
if (BN_cmp(&expected, &value) != 0) {
printf("Unsupported signature version\n");
goto vsb_done;
}
BN_clear(&expected);
BN_clear(&value);
/* Confirm that the length of the image matches with the length in
the authenticated attributes */
length = htobe64(length);
BN_bin2bn((const unsigned char *) &length, sizeof(length), &expected);
ASN1_INTEGER_to_BN(bs->authenticatedAttributes->length, &value);
if (BN_cmp(&expected, &value) != 0) {
printf("Image length doesn't match signature attributes\n");
goto vsb_done;
}
rc = 0;
vsb_done:
BN_free(&expected);
BN_free(&value);
return rc;
}
/**
* Creates a SHA-256 hash from the boot image contents and the encoded
* authenticated attributes.
* @param fd File descriptor to the boot image
* @param length Length of the boot image without the signature block
* @param aa Pointer to AuthAttrs
* @param digest Pointer to a buffer where the hash is written
*/
static int hash_image(int fd, uint64_t length, const AuthAttrs *aa,
unsigned char *digest)
{
EVP_MD_CTX *ctx = NULL;
int rc = -1;
ssize_t bytes = 0;
unsigned char *attrs = NULL;
unsigned char *buffer = NULL;
unsigned char *p = NULL;
uint64_t total = 0;
if (!aa || !digest) {
goto hi_done;
}
if ((buffer = malloc(BUFFER_SIZE)) == NULL) {
goto hi_done;
}
if (lseek64(fd, 0, SEEK_SET) != 0) {
goto hi_done;
}
if ((ctx = EVP_MD_CTX_create()) == NULL) {
ERR_print_errors(g_error);
goto hi_done;
}
EVP_DigestInit(ctx, EVP_sha256());
do {
bytes = BUFFER_SIZE;
if ((length - total) < BUFFER_SIZE) {
bytes = length - total;
}
if ((bytes = read(fd, buffer, bytes)) == -1) {
printf("%s\n", strerror(errno));
goto hi_done;
}
EVP_DigestUpdate(ctx, buffer, bytes);
total += bytes;
} while (total < length);
if ((bytes = i2d_AuthAttrs((AuthAttrs *) aa, NULL)) < 0) {
ERR_print_errors(g_error);
goto hi_done;
}
if ((attrs = OPENSSL_malloc(bytes)) == NULL) {
ERR_print_errors(g_error);
goto hi_done;
}
p = attrs;
if (i2d_AuthAttrs((AuthAttrs *) aa, &p) < 0) {
ERR_print_errors(g_error);
goto hi_done;
}
EVP_DigestUpdate(ctx, attrs, bytes);
EVP_DigestFinal(ctx, digest, NULL);
rc = 0;
hi_done:
if (buffer) {
free(buffer);
}
if (ctx) {
EVP_MD_CTX_destroy(ctx);
}
if (attrs) {
OPENSSL_free(attrs);
}
return rc;
}
/**
* Verifies the RSA signature
* @param fd File descriptor to the boot image
* @param length Length of the boot image without the signature block
* @param bs The boot signature block
*/
static int verify_signature(int fd, uint64_t length, const BootSignature *bs)
{
int rc = -1;
EVP_PKEY *pkey = NULL;
RSA *rsa = NULL;
unsigned char digest[SHA256_DIGEST_LENGTH];
if (!bs) {
goto vs_done;
}
if (hash_image(fd, length, bs->authenticatedAttributes, digest) == -1) {
goto vs_done;
}
if ((pkey = X509_get_pubkey(bs->certificate)) == NULL) {
ERR_print_errors(g_error);
goto vs_done;
}
if ((rsa = EVP_PKEY_get1_RSA(pkey)) == NULL) {
ERR_print_errors(g_error);
goto vs_done;
}
if (!RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH,
bs->signature->data, bs->signature->length, rsa)) {
ERR_print_errors(g_error);
goto vs_done;
}
rc = 0;
vs_done:
if (pkey) {
EVP_PKEY_free(pkey);
}
if (rsa) {
RSA_free(rsa);
}
return rc;
}
/**
* Given the file name of a signed boot image, verifies the signature
* @param image_file Name of the boot image file
*/
static int verify(const char *image_file)
{
BootSignature *bs = NULL;
int fd = -1;
int rc = 1;
off64_t offset = 0;
if (!image_file) {
return rc;
}
if ((fd = open(image_file, O_RDONLY | O_LARGEFILE)) == -1) {
return rc;
}
if (get_signature_offset(fd, &offset) == -1) {
goto out;
}
if (read_signature(fd, offset, &bs) == -1) {
goto out;
}
if (validate_signature_block(bs, offset) == -1) {
goto out;
}
if (verify_signature(fd, offset, bs) == -1) {
goto out;
}
printf("Signature is VALID\n");
rc = 0;
out:
if (bs) {
BootSignature_free(bs);
}
if (fd != -1) {
close(fd);
}
return rc;
}
static void usage()
{
printf("Usage: verify_boot_signature <path-to-boot-image>\n");
}
int main(int argc, char *argv[])
{
if (argc != 2) {
usage();
return 1;
}
/* BIO descriptor for logging OpenSSL errors to stderr */
if ((g_error = BIO_new_fd(STDERR_FILENO, BIO_NOCLOSE)) == NULL) {
printf("Failed to allocate a BIO handle for error output\n");
return 1;
}
ERR_load_crypto_strings();
return verify(argv[1]);
}