/*
* Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
/*
* X509 parser based on mbed TLS
*
* This module implements functions to check the integrity of a X509v3
* certificate ASN.1 structure and extract authentication parameters from the
* extensions field, such as an image hash or a public key.
*/
#include <arch_helpers.h>
#include <assert.h>
#include <img_parser_mod.h>
#include <mbedtls_common.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <utils.h>
/* mbed TLS headers */
#include <mbedtls/asn1.h>
#include <mbedtls/oid.h>
#include <mbedtls/platform.h>
/* Maximum OID string length ("a.b.c.d.e.f ...") */
#define MAX_OID_STR_LEN 64
#define LIB_NAME "mbed TLS X509v3"
/* Temporary variables to speed up the authentication parameters search. These
* variables are assigned once during the integrity check and used any time an
* authentication parameter is requested, so we do not have to parse the image
* again */
static mbedtls_asn1_buf tbs;
static mbedtls_asn1_buf v3_ext;
static mbedtls_asn1_buf pk;
static mbedtls_asn1_buf sig_alg;
static mbedtls_asn1_buf signature;
/*
* Clear all static temporary variables.
*/
static void clear_temp_vars(void)
{
#define ZERO_AND_CLEAN(x) \
do { \
zeromem(&x, sizeof(x)); \
clean_dcache_range((uintptr_t)&x, sizeof(x)); \
} while (0);
ZERO_AND_CLEAN(tbs)
ZERO_AND_CLEAN(v3_ext);
ZERO_AND_CLEAN(pk);
ZERO_AND_CLEAN(sig_alg);
ZERO_AND_CLEAN(signature);
#undef ZERO_AND_CLEAN
}
/*
* Get X509v3 extension
*
* Global variable 'v3_ext' must point to the extensions region
* in the certificate. No need to check for errors since the image has passed
* the integrity check.
*/
static int get_ext(const char *oid, void **ext, unsigned int *ext_len)
{
int oid_len;
size_t len;
unsigned char *end_ext_data, *end_ext_octet;
unsigned char *p;
const unsigned char *end;
char oid_str[MAX_OID_STR_LEN];
mbedtls_asn1_buf extn_oid;
int is_critical;
assert(oid != NULL);
p = v3_ext.p;
end = v3_ext.p + v3_ext.len;
mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
while (p < end) {
zeromem(&extn_oid, sizeof(extn_oid));
is_critical = 0; /* DEFAULT FALSE */
mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
end_ext_data = p + len;
/* Get extension ID */
extn_oid.tag = *p;
mbedtls_asn1_get_tag(&p, end, &extn_oid.len, MBEDTLS_ASN1_OID);
extn_oid.p = p;
p += extn_oid.len;
/* Get optional critical */
mbedtls_asn1_get_bool(&p, end_ext_data, &is_critical);
/* Extension data */
mbedtls_asn1_get_tag(&p, end_ext_data, &len,
MBEDTLS_ASN1_OCTET_STRING);
end_ext_octet = p + len;
/* Detect requested extension */
oid_len = mbedtls_oid_get_numeric_string(oid_str,
MAX_OID_STR_LEN,
&extn_oid);
if (oid_len == MBEDTLS_ERR_OID_BUF_TOO_SMALL) {
return IMG_PARSER_ERR;
}
if ((oid_len == strlen(oid_str)) && !strcmp(oid, oid_str)) {
*ext = (void *)p;
*ext_len = (unsigned int)len;
return IMG_PARSER_OK;
}
/* Next */
p = end_ext_octet;
}
return IMG_PARSER_ERR_NOT_FOUND;
}
/*
* Check the integrity of the certificate ASN.1 structure.
*
* Extract the relevant data that will be used later during authentication.
*
* This function doesn't clear the static variables located on the top of this
* file in case of an error. It is only called from check_integrity(), which
* performs the cleanup if necessary.
*/
static int cert_parse(void *img, unsigned int img_len)
{
int ret, is_critical;
size_t len;
unsigned char *p, *end, *crt_end;
mbedtls_asn1_buf sig_alg1, sig_alg2;
p = (unsigned char *)img;
len = img_len;
end = p + len;
/*
* Certificate ::= SEQUENCE {
* tbsCertificate TBSCertificate,
* signatureAlgorithm AlgorithmIdentifier,
* signatureValue BIT STRING }
*/
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
if (len > (size_t)(end - p)) {
return IMG_PARSER_ERR_FORMAT;
}
crt_end = p + len;
/*
* TBSCertificate ::= SEQUENCE {
*/
tbs.p = p;
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
end = p + len;
tbs.len = end - tbs.p;
/*
* Version ::= INTEGER { v1(0), v2(1), v3(2) }
*/
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 0);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/*
* CertificateSerialNumber ::= INTEGER
*/
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_INTEGER);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/*
* signature AlgorithmIdentifier
*/
sig_alg1.p = p;
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
if ((end - p) < 1) {
return IMG_PARSER_ERR_FORMAT;
}
sig_alg1.len = (p + len) - sig_alg1.p;
p += len;
/*
* issuer Name
*/
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/*
* Validity ::= SEQUENCE {
* notBefore Time,
* notAfter Time }
*
*/
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/*
* subject Name
*/
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/*
* SubjectPublicKeyInfo
*/
pk.p = p;
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
pk.len = (p + len) - pk.p;
p += len;
/*
* issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
*/
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 1);
if (ret != 0) {
if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
return IMG_PARSER_ERR_FORMAT;
}
} else {
p += len;
}
/*
* subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
*/
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 2);
if (ret != 0) {
if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
return IMG_PARSER_ERR_FORMAT;
}
} else {
p += len;
}
/*
* extensions [3] EXPLICIT Extensions OPTIONAL
*/
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 3);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
/*
* Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
*/
v3_ext.p = p;
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
v3_ext.len = (p + len) - v3_ext.p;
/*
* Check extensions integrity
*/
while (p < end) {
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
/* Get extension ID */
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_OID);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/* Get optional critical */
ret = mbedtls_asn1_get_bool(&p, end, &is_critical);
if ((ret != 0) && (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)) {
return IMG_PARSER_ERR_FORMAT;
}
/* Data should be octet string type */
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_OCTET_STRING);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
}
if (p != end) {
return IMG_PARSER_ERR_FORMAT;
}
end = crt_end;
/*
* }
* -- end of TBSCertificate
*
* signatureAlgorithm AlgorithmIdentifier
*/
sig_alg2.p = p;
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
if ((end - p) < 1) {
return IMG_PARSER_ERR_FORMAT;
}
sig_alg2.len = (p + len) - sig_alg2.p;
p += len;
/* Compare both signature algorithms */
if (sig_alg1.len != sig_alg2.len) {
return IMG_PARSER_ERR_FORMAT;
}
if (0 != memcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
return IMG_PARSER_ERR_FORMAT;
}
memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg));
/*
* signatureValue BIT STRING
*/
signature.p = p;
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_BIT_STRING);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
signature.len = (p + len) - signature.p;
p += len;
/* Check certificate length */
if (p != end) {
return IMG_PARSER_ERR_FORMAT;
}
return IMG_PARSER_OK;
}
/* Exported functions */
static void init(void)
{
mbedtls_init();
}
/*
* Wrapper for cert_parse() that clears the static variables used by it in case
* of an error.
*/
static int check_integrity(void *img, unsigned int img_len)
{
int rc = cert_parse(img, img_len);
if (rc != IMG_PARSER_OK)
clear_temp_vars();
return rc;
}
/*
* Extract an authentication parameter from an X509v3 certificate
*
* This function returns a pointer to the extracted data and its length.
* Depending on the type of parameter, a pointer to the data stored in the
* certificate may be returned (i.e. an octet string containing a hash). Other
* data may need to be copied and formatted (i.e. integers). In the later case,
* a buffer of the correct type needs to be statically allocated, filled and
* returned.
*/
static int get_auth_param(const auth_param_type_desc_t *type_desc,
void *img, unsigned int img_len,
void **param, unsigned int *param_len)
{
int rc = IMG_PARSER_OK;
/* We do not use img because the check_integrity function has already
* extracted the relevant data (v3_ext, pk, sig_alg, etc) */
switch (type_desc->type) {
case AUTH_PARAM_RAW_DATA:
/* Data to be signed */
*param = (void *)tbs.p;
*param_len = (unsigned int)tbs.len;
break;
case AUTH_PARAM_HASH:
case AUTH_PARAM_NV_CTR:
/* All these parameters are included as X509v3 extensions */
rc = get_ext(type_desc->cookie, param, param_len);
break;
case AUTH_PARAM_PUB_KEY:
if (type_desc->cookie != 0) {
/* Get public key from extension */
rc = get_ext(type_desc->cookie, param, param_len);
} else {
/* Get the subject public key */
*param = (void *)pk.p;
*param_len = (unsigned int)pk.len;
}
break;
case AUTH_PARAM_SIG_ALG:
/* Get the certificate signature algorithm */
*param = (void *)sig_alg.p;
*param_len = (unsigned int)sig_alg.len;
break;
case AUTH_PARAM_SIG:
/* Get the certificate signature */
*param = (void *)signature.p;
*param_len = (unsigned int)signature.len;
break;
default:
rc = IMG_PARSER_ERR_NOT_FOUND;
break;
}
return rc;
}
REGISTER_IMG_PARSER_LIB(IMG_CERT, LIB_NAME, init, \
check_integrity, get_auth_param);