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>

lib/mbedtls/Kconfig

@@ -116,9 +116,35 @@ endif # LEGACY_CRYPTO_BASIC
 
 config LEGACY_CRYPTO_CERT
 	bool "legacy certificate libraries"
+	select ASYMMETRIC_PUBLIC_KEY_LEGACY if \
+		ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select SPL_ASYMMETRIC_PUBLIC_KEY_LEGACY if \
+		SPL_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
 	help
 	  Enable legacy certificate libraries.
 
+if LEGACY_CRYPTO_CERT
+
+config ASYMMETRIC_PUBLIC_KEY_LEGACY
+	bool "Asymmetric public key crypto with legacy certificate library"
+	depends on LEGACY_CRYPTO_CERT && ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	help
+	  This option chooses legacy certificate library for asymmetric public
+	  key crypto algorithm.
+
+if SPL
+
+config SPL_ASYMMETRIC_PUBLIC_KEY_LEGACY
+	bool "Asymmetric public key crypto with legacy certificate library in SPL"
+	depends on LEGACY_CRYPTO_CERT && SPL_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	help
+	  This option chooses legacy certificate library for asymmetric public
+	  key crypto algorithm in SPL.
+
+endif # SPL
+
+endif # LEGACY_CRYPTO_CERT
+
 endif # LEGACY_CRYPTO
 
 if MBEDTLS_LIB
@@ -255,7 +281,33 @@ endif # MBEDTLS_LIB_CRYPTO
 
 config MBEDTLS_LIB_X509
 	bool "MbedTLS certificate libraries"
+	select ASYMMETRIC_PUBLIC_KEY_MBEDTLS if \
+		ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select SPL_ASYMMETRIC_PUBLIC_KEY_MBEDTLS if \
+		SPL_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
 	help
 	  Enable MbedTLS certificate libraries.
 
+if MBEDTLS_LIB_X509
+
+config ASYMMETRIC_PUBLIC_KEY_MBEDTLS
+	bool "Asymmetric public key crypto with MbedTLS certificate library"
+	depends on MBEDTLS_LIB_X509 && ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	help
+	  This option chooses MbedTLS certificate library for asymmetric public
+	  key crypto algorithm.
+
+if SPL
+
+config SPL_ASYMMETRIC_PUBLIC_KEY_MBEDTLS
+	bool "Asymmetric public key crypto with MbedTLS certificate library in SPL"
+	depends on MBEDTLS_LIB_X509 && SPL_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	help
+	  This option chooses MbedTLS certificate library for asymmetric public
+	  key crypto algorithm in SPL.
+
+endif # SPL
+
+endif # MBEDTLS_LIB_X509
+
 endif # MBEDTLS_LIB

lib/mbedtls/Makefile

@@ -11,6 +11,10 @@ obj-$(CONFIG_$(SPL_)SHA1_MBEDTLS) += sha1.o
 obj-$(CONFIG_$(SPL_)SHA256_MBEDTLS) += sha256.o
 obj-$(CONFIG_$(SPL_)SHA512_MBEDTLS) += sha512.o
 
+# x509 libraries
+obj-$(CONFIG_$(SPL_)ASYMMETRIC_PUBLIC_KEY_MBEDTLS) += \
+	public_key.o
+
 # MbedTLS crypto library
 obj-$(CONFIG_MBEDTLS_LIB) += mbedtls_lib_crypto.o
 mbedtls_lib_crypto-y := \
@@ -36,7 +40,7 @@ mbedtls_lib_x509-$(CONFIG_$(SPL_)RSA_PUBLIC_KEY_PARSER) += \
 	$(MBEDTLS_LIB_DIR)/bignum_core.o \
 	$(MBEDTLS_LIB_DIR)/rsa.o \
 	$(MBEDTLS_LIB_DIR)/rsa_alt_helpers.o
-mbedtls_lib_x509-$(CONFIG_$(SPL_)ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += \
+mbedtls_lib_x509-$(CONFIG_$(SPL_)ASYMMETRIC_PUBLIC_KEY_MBEDTLS) += \
 	$(MBEDTLS_LIB_DIR)/pk.o \
 	$(MBEDTLS_LIB_DIR)/pk_wrap.o \
 	$(MBEDTLS_LIB_DIR)/pkparse.o

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;
+}