[PATCH v2 16/28] mbedtls: add public key porting layer

[Raymond Mao]

Add porting layer for public key on top of MbedTLS X509 library.

Signed-off-by: Raymond Mao <raymond.mao at linaro.org>
---
Changes in v2
- Move the porting layer to MbedTLS dir.

 lib/mbedtls/Makefile     |   4 ++
 lib/mbedtls/public_key.c | 105 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+)
 create mode 100644 lib/mbedtls/public_key.c

diff --git a/lib/mbedtls/Makefile b/lib/mbedtls/Makefile
index b8eda9638f4..cd0144eac1c 100644
--- a/lib/mbedtls/Makefile
+++ b/lib/mbedtls/Makefile
@@ -21,6 +21,10 @@ hash_mbedtls-$(CONFIG_$(SPL_)SHA1) += sha1.o
 hash_mbedtls-$(CONFIG_$(SPL_)SHA256) += sha256.o
 hash_mbedtls-$(CONFIG_$(SPL_)SHA512) += sha512.o
 
+# x509 libraries
+obj-$(CONFIG_MBEDTLS_LIB_X509) += x509_mbedtls.o
+x509_mbedtls-$(CONFIG_$(SPL_)ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key.o
+
 obj-$(CONFIG_MBEDTLS_LIB_CRYPTO) += mbedtls_lib_crypto.o
 mbedtls_lib_crypto-y := \
 	$(MBEDTLS_LIB_DIR)/aes.o \
diff --git a/lib/mbedtls/public_key.c b/lib/mbedtls/public_key.c
new file mode 100644
index 00000000000..2297b4397ba
--- /dev/null
+++ b/lib/mbedtls/public_key.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Public key helper functions using MbedTLS X509 library
+ *
+ * Copyright (c) 2024 Linaro Limited
+ * Author: Raymond Mao <raymond.mao at linaro.org>
+ */
+
+#include <linux/compat.h>
+#include <crypto/public_key.h>
+
+void public_key_free(struct public_key *key)
+{
+	if (key) {
+		kfree(key->key);
+		kfree(key->params);
+		kfree(key);
+	}
+}
+
+void public_key_signature_free(struct public_key_signature *sig)
+{
+	int i;
+
+	if (sig) {
+		for (i = 0; i < ARRAY_SIZE(sig->auth_ids); i++)
+			kfree(sig->auth_ids[i]);
+		kfree(sig->s);
+		kfree(sig->digest);
+		kfree(sig);
+	}
+}
+
+int public_key_verify_signature(const struct public_key *pkey,
+				const struct public_key_signature *sig)
+{
+	mbedtls_md_type_t mb_hash_algo;
+	mbedtls_pk_context pk_ctx;
+	int ret;
+
+	if (!pkey || !sig || pkey->key_is_private)
+		return -EINVAL;
+
+	/*
+	 * ECRDSA (Elliptic Curve RedDSA) from Red Hat is not supported by
+	 * MbedTLS
+	 */
+	if (strcmp(pkey->pkey_algo, "rsa")) {
+		pr_err("Encryption is not RSA: %s\n", sig->pkey_algo);
+		return -EINVAL;
+	}
+
+	/*
+	 * Can be pkcs1 or raw, but pkcs1 is expected.
+	 * This is just for argument checking, not necessarily passed to MbedTLS,
+	 * For RSA signatures, MbedTLS typically supports the PKCS#1 v1.5
+	 * (aka. pkcs1) encoding by default.
+	 * The library internally handles the details of decoding and verifying
+	 * the signature according to the expected encoding for the specified algorithm.
+	 */
+	if (strcmp(sig->encoding, "pkcs1")) {
+		pr_err("Encoding %s is not supported, only supports pkcs1\n",
+		       sig->encoding);
+		return -EINVAL;
+	}
+
+	if (!strcmp(sig->hash_algo, "sha1"))
+		mb_hash_algo = MBEDTLS_MD_SHA1;
+	else if (!strcmp(sig->hash_algo, "sha224"))
+		mb_hash_algo = MBEDTLS_MD_SHA224;
+	else if (!strcmp(sig->hash_algo, "sha256"))
+		mb_hash_algo = MBEDTLS_MD_SHA256;
+	else if (!strcmp(sig->hash_algo, "sha384"))
+		mb_hash_algo = MBEDTLS_MD_SHA384;
+	else if (!strcmp(sig->hash_algo, "sha512"))
+		mb_hash_algo = MBEDTLS_MD_SHA512;
+	else	/* Unknown or unsupported hash algorithm */
+		return -EINVAL;
+	/* Initialize the mbedtls_pk_context with RSA key type */
+	mbedtls_pk_init(&pk_ctx);
+
+	/* Parse the DER-encoded public key */
+	ret = mbedtls_pk_parse_public_key(&pk_ctx, pkey->key, pkey->keylen);
+	if (ret) {
+		pr_err("Failed to parse public key, ret:-0x%04x\n",
+		       (unsigned int)-ret);
+		ret = -EINVAL;
+		goto err_key;
+	}
+
+	/* Ensure that it is a RSA key */
+	if (mbedtls_pk_get_type(&pk_ctx) != MBEDTLS_PK_RSA) {
+		pr_err("Only RSA keys are supported\n");
+		ret = -EKEYREJECTED;
+		goto err_key;
+	}
+
+	/* Verify the hash */
+	ret = mbedtls_pk_verify(&pk_ctx, mb_hash_algo, sig->digest,
+				sig->digest_size, sig->s, sig->s_size);
+
+err_key:
+	mbedtls_pk_free(&pk_ctx);
+	return ret;
+}
-- 
2.25.1