mbedtls: add public key porting layer
Add porting layer for public key on top of MbedTLS X509 library.
Introduce _LEGACY and _MBEDTLS kconfigs for public key legacy and
MbedTLS implementations respectively.
Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/lib/mbedtls/public_key.c b/lib/mbedtls/public_key.c
new file mode 100644
index 0000000..5f73b99
--- /dev/null
+++ b/lib/mbedtls/public_key.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Public key helper functions using MbedTLS X509 library
+ *
+ * Copyright (c) 2024 Linaro Limited
+ * Author: Raymond Mao <raymond.mao@linaro.org>
+ */
+
+#include <linux/compat.h>
+#include <crypto/public_key.h>
+
+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 Russian Digital Signature Algorithm) 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", -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;
+}