[PATCH v3 15/25] mbedtls: add X509 cert parser porting layer

28 May 2024

Add porting layer for X509 cert parser on top of MbedTLS X509
library.
Signed-off-by: Raymond Mao raymond.mao@linaro.org
---
Changes in v2
- Move the porting layer to MbedTLS dir.
Changes in v3
- None.
lib/mbedtls/Makefile           |   1 +
 lib/mbedtls/x509_cert_parser.c | 497 +++++++++++++++++++++++++++++++++
 2 files changed, 498 insertions(+)
 create mode 100644 lib/mbedtls/x509_cert_parser.c

diff --git a/lib/mbedtls/Makefile b/lib/mbedtls/Makefile
index cd0144eac1c..e7cba1ad17c 100644
--- a/lib/mbedtls/Makefile
+++ b/lib/mbedtls/Makefile
@@ -24,6 +24,7 @@ hash_mbedtls-$(CONFIG_$(SPL_)SHA512) += sha512.o
 # x509 libraries
 obj-$(CONFIG_MBEDTLS_LIB_X509) += x509_mbedtls.o
 x509_mbedtls-$(CONFIG_$(SPL_)ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key.o
+x509_mbedtls-$(CONFIG_$(SPL_)X509_CERTIFICATE_PARSER) += x509_cert_parser.o
obj-$(CONFIG_MBEDTLS_LIB_CRYPTO) += mbedtls_lib_crypto.o
 mbedtls_lib_crypto-y := \
diff --git a/lib/mbedtls/x509_cert_parser.c b/lib/mbedtls/x509_cert_parser.c
new file mode 100644
index 00000000000..b0867d31047
--- /dev/null
+++ b/lib/mbedtls/x509_cert_parser.c
@@ -0,0 +1,497 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * X509 cert parser using MbedTLS X509 library
+ *
+ * Copyright (c) 2024 Linaro Limited
+ * Author: Raymond Mao raymond.mao@linaro.org
+ */
+
+#include <linux/err.h>
+#include <crypto/public_key.h>
+#include <crypto/x509_parser.h>
+
+static void x509_free_mbedtls_ctx(struct x509_cert_mbedtls_ctx *ctx)
+{
+	if (ctx) {
+		kfree(ctx->tbs);
+		kfree(ctx->raw_serial);
+		kfree(ctx->raw_issuer);
+		kfree(ctx->raw_subject);
+		kfree(ctx->raw_skid);
+		kfree(ctx);
+	}
+}
+
+static int x509_set_cert_flags(struct x509_certificate *cert)
+{
+	struct public_key_signature *sig = cert->sig;
+
+	if (!sig || !cert->pub) {
+		pr_err("Signature or public key is not initialized\n");
+		return -ENOPKG;
+	}
+
+	if (!cert->pub->pkey_algo)
+		cert->unsupported_key = true;
+
+	if (!sig->pkey_algo)
+		cert->unsupported_sig = true;
+
+	if (!sig->hash_algo)
+		cert->unsupported_sig = true;
+
+	/* TODO: is_hash_blacklisted()? */
+
+	/* Detect self-signed certificates and set self_signed flag */
+	return x509_check_for_self_signed(cert);
+}
+
+/*
+ * Check for self-signedness in an X.509 cert and if found, check the signature
+ * immediately if we can.
+ */
+int x509_check_for_self_signed(struct x509_certificate *cert)
+{
+	int ret = 0;
+
+	if (cert->raw_subject_size != cert->raw_issuer_size ||
+	    memcmp(cert->raw_subject, cert->raw_issuer,
+		   cert->raw_issuer_size) != 0)
+		goto not_self_signed;
+
+	if (cert->sig->auth_ids[0] || cert->sig->auth_ids[1]) {
+		/* If the AKID is present it may have one or two parts.  If
+		 * both are supplied, both must match.
+		 */
+		bool a = asymmetric_key_id_same(cert->skid, cert->sig->auth_ids[1]);
+		bool b = asymmetric_key_id_same(cert->id, cert->sig->auth_ids[0]);
+
+		if (!a && !b)
+			goto not_self_signed;
+
+		ret = -EKEYREJECTED;
+		if (((a && !b) || (b && !a)) &&
+		    cert->sig->auth_ids[0] && cert->sig->auth_ids[1])
+			goto out;
+	}
+
+	ret = -EKEYREJECTED;
+	if (strcmp(cert->pub->pkey_algo, cert->sig->pkey_algo) != 0)
+		goto out;
+
+	ret = public_key_verify_signature(cert->pub, cert->sig);
+	if (ret < 0) {
+		if (ret == -ENOPKG) {
+			cert->unsupported_sig = true;
+			ret = 0;
+		}
+		goto out;
+	}
+
+	pr_devel("Cert Self-signature verified");
+	cert->self_signed = true;
+
+out:
+	return ret;
+
+not_self_signed:
+	return 0;
+}
+
+time64_t x509_get_timestamp(const mbedtls_x509_time *x509_time)
+{
+	unsigned int year, mon, day, hour, min, sec;
+
+	/* Adjust for year since 1900 */
+	year = x509_time->year - 1900;
+	/* Adjust for 0-based month */
+	mon = x509_time->mon - 1;
+	day = x509_time->day;
+	hour = x509_time->hour;
+	min = x509_time->min;
+	sec = x509_time->sec;
+
+	return (time64_t)mktime64(year, mon, day, hour, min, sec);
+}
+
+static char *x509_populate_dn_name_string(const mbedtls_x509_name *name)
+{
+	size_t len = 256;
+	size_t wb;
+	char *name_str;
+
+	do {
+		name_str = kzalloc(len, GFP_KERNEL);
+		if (!name_str)
+			return NULL;
+
+		wb = mbedtls_x509_dn_gets(name_str, len, name);
+		if (wb < 0) {
+			pr_err("Get DN string failed, ret:-0x%04x\n",
+			       (unsigned int)-wb);
+			kfree(name_str);
+			len = len * 2; /* Try with a bigger buffer */
+		}
+	} while (wb < 0);
+
+	name_str[wb] = '\0'; /* add the terminator */
+
+	return name_str;
+}
+
+static int x509_populate_signature_params(const mbedtls_x509_crt *cert,
+					  struct public_key_signature **sig)
+{
+	struct public_key_signature *s;
+	struct image_region region;
+	size_t akid_len;
+	unsigned char *akid_data;
+	int ret;
+
+	/* Check if signed data exist */
+	if (!cert->tbs.p || !cert->tbs.len)
+		return -EINVAL;
+
+	region.data = cert->tbs.p;
+	region.size = cert->tbs.len;
+
+	s = kzalloc(sizeof(*s), GFP_KERNEL);
+	if (!s)
+		return -ENOMEM;
+
+	/*
+	 * Get the public key algorithm.
+	 * Note: ECRDSA (Elliptic Curve RedDSA) from Red Hat is not supported by
+	 *	 MbedTLS.
+	 */
+	switch (cert->sig_pk) {
+	case MBEDTLS_PK_RSA:
+		s->pkey_algo = "rsa";
+		break;
+	default:
+		ret = -EINVAL;
+		goto error_sig;
+	}
+
+	/* Get the hash algorithm */
+	switch (cert->sig_md) {
+	case MBEDTLS_MD_SHA1:
+		s->hash_algo = "sha1";
+		s->digest_size = SHA1_SUM_LEN;
+		break;
+	case MBEDTLS_MD_SHA256:
+		s->hash_algo = "sha256";
+		s->digest_size = SHA256_SUM_LEN;
+		break;
+	case MBEDTLS_MD_SHA384:
+		s->hash_algo = "sha384";
+		s->digest_size = SHA384_SUM_LEN;
+		break;
+	case MBEDTLS_MD_SHA512:
+		s->hash_algo = "sha512";
+		s->digest_size = SHA512_SUM_LEN;
+		break;
+	/* Unsupported algo */
+	case MBEDTLS_MD_MD5:
+	case MBEDTLS_MD_SHA224:
+	default:
+		ret = -EINVAL;
+		goto error_sig;
+	}
+
+	/*
+	 * Optional attributes:
+	 * auth_ids holds AuthorityKeyIdentifier (information of issuer),
+	 * aka akid, which is used to match with a cert's id or skid to
+	 * indicate that is the issuer when we lookup a cert chain.
+	 *
+	 * auth_ids[0]:
+	 *	[PKCS#7 or CMS ver 1] - generated from "Issuer + Serial number"
+	 *	[CMS ver 3] - generated from skid (subjectKeyId)
+	 * auth_ids[1]: generated from skid (subjectKeyId)
+	 *
+	 * Assume that we are using PKCS#7 (msg->version=1),
+	 * not CMS ver 3 (msg->version=3).
+	 */
+	akid_len = cert->authority_key_id.authorityCertSerialNumber.len;
+	akid_data = cert->authority_key_id.authorityCertSerialNumber.p;
+
+	/* Check if serial number exists */
+	if (akid_len && akid_data) {
+		s->auth_ids[0] = asymmetric_key_generate_id(akid_data,
+							    akid_len,
+							    cert->issuer_raw.p,
+							    cert->issuer_raw.len);
+		if (!s->auth_ids[0]) {
+			ret = -ENOMEM;
+			goto error_sig;
+		}
+	}
+
+	akid_len = cert->authority_key_id.keyIdentifier.len;
+	akid_data = cert->authority_key_id.keyIdentifier.p;
+
+	/* Check if subjectKeyId exists */
+	if (akid_len && akid_data) {
+		s->auth_ids[1] = asymmetric_key_generate_id(akid_data,
+							    akid_len,
+							    "", 0);
+		if (!s->auth_ids[1]) {
+			ret = -ENOMEM;
+			goto error_sig;
+		}
+	}
+
+	/*
+	 * Encoding can be pkcs1 or raw, but only pkcs1 is supported.
+	 * Set the encoding explicitly to pkcs1.
+	 */
+	s->encoding = "pkcs1";
+
+	/* Copy the signature data */
+	s->s = kmemdup(cert->sig.p, cert->sig.len, GFP_KERNEL);
+	if (!s->s) {
+		ret = -ENOMEM;
+		goto error_sig;
+	}
+	s->s_size = cert->sig.len;
+
+	/* Calculate the digest of signed data (tbs) */
+	s->digest = kzalloc(s->digest_size, GFP_KERNEL);
+	if (!s->digest) {
+		ret = -ENOMEM;
+		goto error_sig;
+	}
+
+	ret = hash_calculate(s->hash_algo, &region, 1, s->digest);
+	if (!ret)
+		*sig = s;
+
+	return ret;
+
+error_sig:
+	public_key_signature_free(s);
+	return ret;
+}
+
+static int x509_save_mbedtls_ctx(const mbedtls_x509_crt *cert,
+				 struct x509_cert_mbedtls_ctx **pctx)
+{
+	struct x509_cert_mbedtls_ctx *ctx;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	/* Signed data (tbs - The part that is To Be Signed)*/
+	ctx->tbs = kmemdup(cert->tbs.p, cert->tbs.len,
+			   GFP_KERNEL);
+	if (!ctx->tbs)
+		goto error_ctx;
+
+	/* Raw serial number */
+	ctx->raw_serial = kmemdup(cert->serial.p,
+				  cert->serial.len, GFP_KERNEL);
+	if (!ctx->raw_serial)
+		goto error_ctx;
+
+	/* Raw issuer */
+	ctx->raw_issuer = kmemdup(cert->issuer_raw.p,
+				  cert->issuer_raw.len, GFP_KERNEL);
+	if (!ctx->raw_issuer)
+		goto error_ctx;
+
+	/* Raw subject */
+	ctx->raw_subject = kmemdup(cert->subject_raw.p,
+				   cert->subject_raw.len, GFP_KERNEL);
+	if (!ctx->raw_subject)
+		goto error_ctx;
+
+	/* Raw subjectKeyId */
+	ctx->raw_skid = kmemdup(cert->subject_key_id.p,
+				cert->subject_key_id.len, GFP_KERNEL);
+	if (!ctx->raw_skid)
+		goto error_ctx;
+
+	*pctx = ctx;
+
+	return 0;
+
+error_ctx:
+	x509_free_mbedtls_ctx(ctx);
+	return -ENOMEM;
+}
+
+/*
+ * Free an X.509 certificate
+ */
+void x509_free_certificate(struct x509_certificate *cert)
+{
+	if (cert) {
+		public_key_free(cert->pub);
+		public_key_signature_free(cert->sig);
+		kfree(cert->issuer);
+		kfree(cert->subject);
+		kfree(cert->id);
+		kfree(cert->skid);
+		x509_free_mbedtls_ctx(cert->mbedtls_ctx);
+		kfree(cert);
+	}
+}
+
+int x509_populate_pubkey(mbedtls_x509_crt *cert, struct public_key **pub_key)
+{
+	struct public_key *pk;
+
+	pk = kzalloc(sizeof(*pk), GFP_KERNEL);
+	if (!pk)
+		return -ENOMEM;
+
+	pk->key = kzalloc(cert->pk_raw.len, GFP_KERNEL);
+	if (!pk->key) {
+		kfree(pk);
+		return -ENOMEM;
+	}
+	memcpy(pk->key, cert->pk_raw.p, cert->pk_raw.len);
+	pk->keylen = cert->pk_raw.len;
+
+	/*
+	 * For ECC keys, params field might include information about the curve used,
+	 * the generator point, or other algorithm-specific parameters.
+	 * For RSA keys, it's common for the params field to be NULL.
+	 * FIXME: Assume that we just support RSA keys with id_type X509.
+	 */
+	pk->params = NULL;
+	pk->paramlen = 0;
+
+	pk->key_is_private = false;
+	pk->id_type = "X509";
+	pk->pkey_algo = "rsa";
+	pk->algo = OID_rsaEncryption;
+
+	*pub_key = pk;
+
+	return 0;
+}
+
+int x509_populate_cert(mbedtls_x509_crt *mbedtls_cert,
+		       struct x509_certificate **pcert)
+{
+	struct x509_certificate *cert;
+	struct asymmetric_key_id *kid;
+	struct asymmetric_key_id *skid;
+	int ret;
+
+	cert = kzalloc(sizeof(*cert), GFP_KERNEL);
+	if (!cert)
+		return -ENOMEM;
+
+	/* Public key details */
+	ret = x509_populate_pubkey(mbedtls_cert, &cert->pub);
+	if (ret)
+		goto error_cert_pop;
+
+	/* Signature parameters */
+	ret = x509_populate_signature_params(mbedtls_cert, &cert->sig);
+	if (ret)
+		goto error_cert_pop;
+
+	ret = -ENOMEM;
+
+	/* Name of certificate issuer */
+	cert->issuer = x509_populate_dn_name_string(&mbedtls_cert->issuer);
+	if (!cert->issuer)
+		goto error_cert_pop;
+
+	/* Name of certificate subject */
+	cert->subject = x509_populate_dn_name_string(&mbedtls_cert->subject);
+	if (!cert->subject)
+		goto error_cert_pop;
+
+	/* Certificate validity */
+	cert->valid_from = x509_get_timestamp(&mbedtls_cert->valid_from);
+	cert->valid_to = x509_get_timestamp(&mbedtls_cert->valid_to);
+
+	/* Save mbedtls context we need */
+	ret = x509_save_mbedtls_ctx(mbedtls_cert, &cert->mbedtls_ctx);
+	if (ret)
+		goto error_cert_pop;
+
+	/* Signed data (tbs - The part that is To Be Signed)*/
+	cert->tbs = cert->mbedtls_ctx->tbs;
+	cert->tbs_size = mbedtls_cert->tbs.len;
+
+	/* Raw serial number */
+	cert->raw_serial = cert->mbedtls_ctx->raw_serial;
+	cert->raw_serial_size = mbedtls_cert->serial.len;
+
+	/* Raw issuer */
+	cert->raw_issuer = cert->mbedtls_ctx->raw_issuer;
+	cert->raw_issuer_size = mbedtls_cert->issuer_raw.len;
+
+	/* Raw subject */
+	cert->raw_subject = cert->mbedtls_ctx->raw_subject;
+	cert->raw_subject_size = mbedtls_cert->subject_raw.len;
+
+	/* Raw subjectKeyId */
+	cert->raw_skid = cert->mbedtls_ctx->raw_skid;
+	cert->raw_skid_size = mbedtls_cert->subject_key_id.len;
+
+	/* Generate cert issuer + serial number key ID */
+	kid = asymmetric_key_generate_id(cert->raw_serial,
+					 cert->raw_serial_size,
+					 cert->raw_issuer,
+					 cert->raw_issuer_size);
+	if (IS_ERR(kid)) {
+		ret = PTR_ERR(kid);
+		goto error_cert_pop;
+	}
+	cert->id = kid;
+
+	/* Generate subject + subjectKeyId */
+	skid = asymmetric_key_generate_id(cert->raw_skid, cert->raw_skid_size, "", 0);
+	if (IS_ERR(skid)) {
+		ret = PTR_ERR(skid);
+		goto error_cert_pop;
+	}
+	cert->skid = skid;
+
+	/*
+	 * Set the certificate flags:
+	 * self_signed, unsupported_key, unsupported_sig, blacklisted
+	 */
+	ret = x509_set_cert_flags(cert);
+	if (!ret) {
+		*pcert = cert;
+		return 0;
+	}
+
+error_cert_pop:
+	x509_free_certificate(cert);
+	return ret;
+}
+
+struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
+{
+	mbedtls_x509_crt mbedtls_cert;
+	struct x509_certificate *cert = NULL;
+	long ret;
+
+	/* Parse DER encoded certificate */
+	mbedtls_x509_crt_init(&mbedtls_cert);
+	ret = mbedtls_x509_crt_parse_der(&mbedtls_cert, data, datalen);
+	if (ret)
+		goto clean_up_ctx;
+
+	/* Populate x509_certificate from mbedtls_x509_crt */
+	ret = x509_populate_cert(&mbedtls_cert, &cert);
+	if (ret)
+		goto clean_up_ctx;
+
+clean_up_ctx:
+	mbedtls_x509_crt_free(&mbedtls_cert);
+	if (!ret)
+		return cert;
+
+	return ERR_PTR(ret);
+}
-- 
2.25.1


    