1 files changed, 82 insertions, 0 deletions
diff --git a/lib/mbedtls/public_key.c b/lib/mbedtls/public_key.c
new file mode 100644
index 00000000000..5f73b99d4f2
--- /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;
+}