blob: 65fa85a9fc853253d105dce22fab522b915152d1 [file] [log] [blame]
/*
* Copyright (c) 2015-2023, 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 <assert.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
/* mbed TLS headers */
#include <mbedtls/asn1.h>
#include <mbedtls/oid.h>
#include <mbedtls/platform.h>
#include <arch_helpers.h>
#include <drivers/auth/img_parser_mod.h>
#include <drivers/auth/mbedtls/mbedtls_common.h>
#include <lib/utils.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. OID may be NULL to request that get_ext()
* is only being called for integrity checking.
*/
static int get_ext(const char *oid, void **ext, unsigned int *ext_len)
{
int oid_len, ret, is_critical;
size_t len;
unsigned char *p;
const unsigned char *end;
char oid_str[MAX_OID_STR_LEN];
mbedtls_asn1_buf extn_oid;
p = v3_ext.p;
end = v3_ext.p + v3_ext.len;
/*
* Check extensions integrity. At least one extension is
* required: the ASN.1 specifies a minimum size of 1, and at
* least one extension is needed to authenticate the next stage
* in the boot chain.
*/
do {
unsigned char *end_ext_data;
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
end_ext_data = p + len;
/* Get extension ID */
ret = mbedtls_asn1_get_tag(&p, end_ext_data, &extn_oid.len,
MBEDTLS_ASN1_OID);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
extn_oid.tag = MBEDTLS_ASN1_OID;
extn_oid.p = p;
p += extn_oid.len;
/* Get optional critical */
ret = mbedtls_asn1_get_bool(&p, end_ext_data, &is_critical);
if ((ret != 0) && (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)) {
return IMG_PARSER_ERR_FORMAT;
}
/*
* Data should be octet string type and must use all bytes in
* the Extension.
*/
ret = mbedtls_asn1_get_tag(&p, end_ext_data, &len,
MBEDTLS_ASN1_OCTET_STRING);
if ((ret != 0) || ((p + len) != end_ext_data)) {
return IMG_PARSER_ERR_FORMAT;
}
/* 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) || (oid_len < 0)) {
return IMG_PARSER_ERR;
}
if ((oid != NULL) &&
((size_t)oid_len == strlen(oid_str)) &&
(strcmp(oid, oid_str) == 0)) {
*ext = (void *)p;
*ext_len = (unsigned int)len;
return IMG_PARSER_OK;
}
/* Next */
p = end_ext_data;
} while (p < end);
return (oid == NULL) ? IMG_PARSER_OK : 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;
size_t len;
unsigned char *p, *end, *crt_end, *pk_end;
mbedtls_asn1_buf sig_alg1;
/*
* The unique ASN.1 DER encoding of [0] EXPLICIT INTEGER { v3(2} }.
*/
static const char v3[] = {
/* The outer CONTEXT SPECIFIC 0 tag */
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_CONTEXT_SPECIFIC | 0,
/* The number bytes used to encode the inner INTEGER */
3,
/* The tag of the inner INTEGER */
MBEDTLS_ASN1_INTEGER,
/* The number of bytes needed to represent 2 */
1,
/* The actual value 2 */
2,
};
p = (unsigned char *)img;
len = img_len;
crt_end = p + len;
end = crt_end;
/*
* 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) || ((p + len) != end)) {
return IMG_PARSER_ERR_FORMAT;
}
/*
* 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 ::= [0] EXPLICIT INTEGER { v1(0), v2(1), v3(2) }
* -- only v3 accepted
*/
if (((end - p) <= (ptrdiff_t)sizeof(v3)) ||
(memcmp(p, v3, sizeof(v3)) != 0)) {
return IMG_PARSER_ERR_FORMAT;
}
p += sizeof(v3);
/*
* 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;
}
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_end = p + len;
pk.len = pk_end - pk.p;
/* algorithm */
ret = mbedtls_asn1_get_tag(&p, pk_end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
/* Key is a BIT STRING and must use all bytes in SubjectPublicKeyInfo */
ret = mbedtls_asn1_get_bitstring_null(&p, pk_end, &len);
if ((ret != 0) || (p + len != pk_end)) {
return IMG_PARSER_ERR_FORMAT;
}
p = pk_end;
/*
* issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
* subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL,
* -- technically these contain BIT STRINGs but that is not worth
* -- validating
*/
for (int i = 1; i < 3; i++) {
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | i);
/*
* Unique IDs are obsolete, so MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
* is the common case.
*/
if (ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
if (ret != 0) {
return IMG_PARSER_ERR_FORMAT;
}
p += len;
}
}
/*
* extensions [3] EXPLICIT Extensions OPTIONAL
* }
*
* X.509 and RFC5280 allow omitting the extensions entirely.
* However, in TF-A, a certificate with no extensions would
* always fail later on, as the extensions contain the
* information needed to authenticate the next stage in the
* boot chain. Furthermore, get_ext() assumes that the
* extensions have been parsed into v3_ext, and allowing
* there to be no extensions would pointlessly complicate
* the code. Therefore, just reject certificates without
* extensions. This is also why version 1 and 2 certificates
* are rejected above.
*/
ret = mbedtls_asn1_get_tag(&p, end, &len,
MBEDTLS_ASN1_CONTEXT_SPECIFIC |
MBEDTLS_ASN1_CONSTRUCTED | 3);
if ((ret != 0) || (len != (size_t)(end - p))) {
return IMG_PARSER_ERR_FORMAT;
}
/*
* Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
* -- must use all remaining bytes in TBSCertificate
*/
ret = mbedtls_asn1_get_tag(&p, end, &len, MBEDTLS_ASN1_CONSTRUCTED |
MBEDTLS_ASN1_SEQUENCE);
if ((ret != 0) || (len != (size_t)(end - p))) {
return IMG_PARSER_ERR_FORMAT;
}
v3_ext.p = p;
v3_ext.len = len;
p += len;
/* Check extensions integrity */
ret = get_ext(NULL, NULL, NULL);
if (ret != IMG_PARSER_OK) {
return ret;
}
end = crt_end;
/*
* }
* -- end of TBSCertificate
*
* signatureAlgorithm AlgorithmIdentifier
* -- Does not need to be parsed. Ensuring it is bitwise
* -- identical (including the tag!) with the first signature
* -- algorithm is sufficient.
*/
if ((sig_alg1.len >= (size_t)(end - p)) ||
(0 != memcmp(sig_alg1.p, p, sig_alg1.len))) {
return IMG_PARSER_ERR_FORMAT;
}
p += sig_alg1.len;
memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg));
/*
* signatureValue BIT STRING
* } -- must consume all bytes
*/
signature.p = p;
ret = mbedtls_asn1_get_bitstring_null(&p, end, &len);
if ((ret != 0) || ((p + len) != end)) {
return IMG_PARSER_ERR_FORMAT;
}
signature.len = end - signature.p;
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 != NULL) {
/* 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);