X.509: support OSCCA SM2-with-SM3 certificate verification

The digital certificate format based on SM2 crypto algorithm as
specified in GM/T 0015-2012. It was published by State Encryption
Management Bureau, China.

The method of generating Other User Information is defined as
ZA=H256(ENTLA || IDA || a || b || xG || yG || xA || yA), it also
specified in https://tools.ietf.org/html/draft-shen-sm2-ecdsa-02.

The x509 certificate supports SM2-with-SM3 type certificate
verification. Because certificate verification requires ZA
in addition to tbs data, ZA also depends on elliptic curve
parameters and public key data, so you need to access tbs in sig
and calculate ZA. Finally calculate the digest of the
signature and complete the verification work. The calculation
process of ZA is declared in specifications GM/T 0009-2012
and GM/T 0003.2-2012.

Signed-off-by: Tianjia Zhang <[e-mail]>
Tested-by: Xufeng Zhang <[e-mail]>
Reviewed-by: Gilad Ben-Yossef <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

crypto/asymmetric_keys/Makefile

···
 	signature.o
 
 obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key.o
+obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key_sm2.o
 obj-$(CONFIG_ASYMMETRIC_TPM_KEY_SUBTYPE) += asym_tpm.o
 
 #

crypto/asymmetric_keys/public_key.c

···
 	if (ret)
 		goto error_free_key;
 
+	if (strcmp(sig->pkey_algo, "sm2") == 0 && sig->data_size) {
+		ret = cert_sig_digest_update(sig, tfm);
+		if (ret)
+			goto error_free_key;
+	}
+
 	sg_init_table(src_sg, 2);
 	sg_set_buf(&src_sg[0], sig->s, sig->s_size);
 	sg_set_buf(&src_sg[1], sig->digest, sig->digest_size);

crypto/asymmetric_keys/public_key_sm2.c

···
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * asymmetric public-key algorithm for SM2-with-SM3 certificate
+ * as specified by OSCCA GM/T 0003.1-2012 -- 0003.5-2012 SM2 and
+ * described at https://tools.ietf.org/html/draft-shen-sm2-ecdsa-02
+ *
+ * Copyright (c) 2020, Alibaba Group.
+ * Authors: Tianjia Zhang <[e-mail]>
+ */
+
+#include <crypto/sm3_base.h>
+#include <crypto/sm2.h>
+#include <crypto/public_key.h>
+
+#if IS_REACHABLE(CONFIG_CRYPTO_SM2)
+
+int cert_sig_digest_update(const struct public_key_signature *sig,
+				struct crypto_akcipher *tfm_pkey)
+{
+	struct crypto_shash *tfm;
+	struct shash_desc *desc;
+	size_t desc_size;
+	unsigned char dgst[SM3_DIGEST_SIZE];
+	int ret;
+
+	BUG_ON(!sig->data);
+
+	ret = sm2_compute_z_digest(tfm_pkey, SM2_DEFAULT_USERID,
+					SM2_DEFAULT_USERID_LEN, dgst);
+	if (ret)
+		return ret;
+
+	tfm = crypto_alloc_shash(sig->hash_algo, 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
+	desc = kzalloc(desc_size, GFP_KERNEL);
+	if (!desc)
+		goto error_free_tfm;
+
+	desc->tfm = tfm;
+
+	ret = crypto_shash_init(desc);
+	if (ret < 0)
+		goto error_free_desc;
+
+	ret = crypto_shash_update(desc, dgst, SM3_DIGEST_SIZE);
+	if (ret < 0)
+		goto error_free_desc;
+
+	ret = crypto_shash_finup(desc, sig->data, sig->data_size, sig->digest);
+
+error_free_desc:
+	kfree(desc);
+error_free_tfm:
+	crypto_free_shash(tfm);
+	return ret;
+}
+
+#endif /* ! IS_REACHABLE(CONFIG_CRYPTO_SM2) */

crypto/asymmetric_keys/x509_public_key.c

···
 
 	pr_devel("==>%s()\n", __func__);
 
+	sig->data = cert->tbs;
+	sig->data_size = cert->tbs_size;
+
 	if (!cert->pub->pkey_algo)
 		cert->unsupported_key = true;
 

include/crypto/public_key.h

···
 
 #include <linux/keyctl.h>
 #include <linux/oid_registry.h>
+#include <crypto/akcipher.h>
 
 /*
  * Cryptographic data for the public-key subtype of the asymmetric key type.
···
 	const char *pkey_algo;
 	const char *hash_algo;
 	const char *encoding;
+	const void *data;
+	unsigned int data_size;
 };
 
 extern void public_key_signature_free(struct public_key_signature *sig);
···
 
 int public_key_verify_signature(const struct public_key *pkey,
 				const struct public_key_signature *sig);
+
+#if IS_REACHABLE(CONFIG_CRYPTO_SM2)
+int cert_sig_digest_update(const struct public_key_signature *sig,
+				struct crypto_akcipher *tfm_pkey);
+#else
+static inline
+int cert_sig_digest_update(const struct public_key_signature *sig,
+				struct crypto_akcipher *tfm_pkey)
+{
+	return -ENOTSUPP;
+}
+#endif
 
 #endif /* _LINUX_PUBLIC_KEY_H */