mbedtls: add RSA helper layer on MbedTLS

Add RSA helper layer on top on MbedTLS PK and RSA library.
Introduce _LEGACY and _MBEDTLS kconfigs for RSA helper legacy and
MbedTLS implementations respectively.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

lib/mbedtls/Kconfig

@@ -118,11 +118,13 @@ config LEGACY_CRYPTO_CERT
 	bool "legacy certificate libraries"
 	select ASYMMETRIC_PUBLIC_KEY_LEGACY if \
 		ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select RSA_PUBLIC_KEY_PARSER_LEGACY if RSA_PUBLIC_KEY_PARSER
 	select X509_CERTIFICATE_PARSER_LEGACY if X509_CERTIFICATE_PARSER
 	select PKCS7_MESSAGE_PARSER_LEGACY if PKCS7_MESSAGE_PARSER
 	select MSCODE_PARSER_LEGACY if MSCODE_PARSER
 	select SPL_ASYMMETRIC_PUBLIC_KEY_LEGACY if \
 		SPL_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select SPL_RSA_PUBLIC_KEY_PARSER_LEGACY if SPL_RSA_PUBLIC_KEY_PARSER
 	help
 	  Enable legacy certificate libraries.
 
@@ -135,6 +137,14 @@ config ASYMMETRIC_PUBLIC_KEY_LEGACY
 	  This option chooses legacy certificate library for asymmetric public
 	  key crypto algorithm.
 
+config RSA_PUBLIC_KEY_PARSER_LEGACY
+	bool "RSA public key parser with legacy certificate library"
+	depends on ASYMMETRIC_PUBLIC_KEY_LEGACY
+	select ASN1_DECODER_LEGACY
+	help
+	  This option chooses legacy certificate library for RSA public key
+	  parser.
+
 config X509_CERTIFICATE_PARSER_LEGACY
 	bool "X.509 certificate parser with legacy certificate library"
 	depends on ASYMMETRIC_PUBLIC_KEY_LEGACY
@@ -168,6 +178,14 @@ config SPL_ASYMMETRIC_PUBLIC_KEY_LEGACY
 	  This option chooses legacy certificate library for asymmetric public
 	  key crypto algorithm in SPL.
 
+config SPL_RSA_PUBLIC_KEY_PARSER_LEGACY
+	bool "RSA public key parser with legacy certificate library in SPL"
+	depends on SPL_ASYMMETRIC_PUBLIC_KEY_LEGACY
+	select SPL_ASN1_DECODER_LEGACY
+	help
+	  This option chooses legacy certificate library for RSA public key
+	  parser in SPL.
+
 endif # SPL
 
 endif # LEGACY_CRYPTO_CERT
@@ -310,11 +328,13 @@ config MBEDTLS_LIB_X509
 	bool "MbedTLS certificate libraries"
 	select ASYMMETRIC_PUBLIC_KEY_MBEDTLS if \
 		ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select RSA_PUBLIC_KEY_PARSER_MBEDTLS if RSA_PUBLIC_KEY_PARSER
 	select X509_CERTIFICATE_PARSER_MBEDTLS if X509_CERTIFICATE_PARSER
 	select PKCS7_MESSAGE_PARSER_MBEDTLS if PKCS7_MESSAGE_PARSER
 	select MSCODE_PARSER_MBEDTLS if MSCODE_PARSER
 	select SPL_ASYMMETRIC_PUBLIC_KEY_MBEDTLS if \
 		SPL_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select SPL_RSA_PUBLIC_KEY_PARSER_MBEDTLS if SPL_RSA_PUBLIC_KEY_PARSER
 	help
 	  Enable MbedTLS certificate libraries.
 
@@ -327,6 +347,14 @@ config ASYMMETRIC_PUBLIC_KEY_MBEDTLS
 	  This option chooses MbedTLS certificate library for asymmetric public
 	  key crypto algorithm.
 
+config RSA_PUBLIC_KEY_PARSER_MBEDTLS
+	bool "RSA public key parser with MbedTLS certificate library"
+	depends on ASYMMETRIC_PUBLIC_KEY_MBEDTLS
+	select ASN1_DECODER_MBEDTLS
+	help
+	  This option chooses MbedTLS certificate library for RSA public key
+	  parser.
+
 config X509_CERTIFICATE_PARSER_MBEDTLS
 	bool "X.509 certificate parser with MbedTLS certificate library"
 	depends on ASYMMETRIC_PUBLIC_KEY_MBEDTLS
@@ -360,6 +388,14 @@ config SPL_ASYMMETRIC_PUBLIC_KEY_MBEDTLS
 	  This option chooses MbedTLS certificate library for asymmetric public
 	  key crypto algorithm in SPL.
 
+config SPL_RSA_PUBLIC_KEY_PARSER_MBEDTLS
+	bool "RSA public key parser with MbedTLS certificate library in SPL"
+	depends on SPL_ASYMMETRIC_PUBLIC_KEY_MBEDTLS
+	select SPL_ASN1_DECODER_MBEDTLS
+	help
+	  This option chooses MbedTLS certificate library for RSA public key
+	  parser in SPL.
+
 endif # SPL
 
 endif # MBEDTLS_LIB_X509

lib/mbedtls/Makefile

@@ -18,6 +18,7 @@ obj-$(CONFIG_$(SPL_)X509_CERTIFICATE_PARSER_MBEDTLS) += \
 	x509_cert_parser.o
 obj-$(CONFIG_$(SPL_)PKCS7_MESSAGE_PARSER_MBEDTLS) += pkcs7_parser.o
 obj-$(CONFIG_$(SPL_)MSCODE_PARSER_MBEDTLS) += mscode_parser.o
+obj-$(CONFIG_$(SPL_)RSA_PUBLIC_KEY_PARSER_MBEDTLS) += rsa_helper.o
 
 # MbedTLS crypto library
 obj-$(CONFIG_MBEDTLS_LIB) += mbedtls_lib_crypto.o
@@ -39,7 +40,7 @@ mbedtls_lib_x509-$(CONFIG_$(SPL_)ASN1_DECODER) += \
 	$(MBEDTLS_LIB_DIR)/asn1parse.o \
 	$(MBEDTLS_LIB_DIR)/asn1write.o \
 	$(MBEDTLS_LIB_DIR)/oid.o
-mbedtls_lib_x509-$(CONFIG_$(SPL_)RSA_PUBLIC_KEY_PARSER) += \
+mbedtls_lib_x509-$(CONFIG_$(SPL_)RSA_PUBLIC_KEY_PARSER_MBEDTLS) += \
 	$(MBEDTLS_LIB_DIR)/bignum.o \
 	$(MBEDTLS_LIB_DIR)/bignum_core.o \
 	$(MBEDTLS_LIB_DIR)/rsa.o \

lib/mbedtls/rsa_helper.c

@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * RSA helper functions using MbedTLS
+ *
+ * Copyright (c) 2024 Linaro Limited
+ * Author: Raymond Mao <raymond.mao@linaro.org>
+ */
+
+#include <linux/err.h>
+#include <crypto/internal/rsa.h>
+#include <library/common.h>
+#include <mbedtls/pk.h>
+#include <mbedtls/rsa.h>
+#include <mbedtls/asn1.h>
+
+/**
+ * rsa_parse_pub_key() - decodes the BER encoded buffer and stores in the
+ *                       provided struct rsa_key, pointers to the raw key as is,
+ *                       so that the caller can copy it or MPI parse it, etc.
+ *
+ * @rsa_key:	struct rsa_key key representation
+ * @key:	key in BER format
+ * @key_len:	length of key
+ *
+ * Return:	0 on success or error code in case of error
+ */
+int rsa_parse_pub_key(struct rsa_key *rsa_key, const void *key,
+		      unsigned int key_len)
+{
+	int ret = 0;
+	mbedtls_pk_context pk;
+	mbedtls_rsa_context *rsa;
+
+	mbedtls_pk_init(&pk);
+
+	ret = mbedtls_pk_parse_public_key(&pk, (const unsigned char *)key,
+					  key_len);
+	if (ret) {
+		pr_err("Failed to parse public key, ret:-0x%04x\n", -ret);
+		ret = -EINVAL;
+		goto clean_pubkey;
+	}
+
+	/* Ensure that it is a RSA key */
+	if (mbedtls_pk_get_type(&pk) != MBEDTLS_PK_RSA) {
+		pr_err("Non-RSA keys are not supported\n");
+		ret = -EKEYREJECTED;
+		goto clean_pubkey;
+	}
+
+	/* Get RSA key context */
+	rsa = mbedtls_pk_rsa(pk);
+	if (!rsa) {
+		pr_err("Failed to get RSA key context, ret:-0x%04x\n", -ret);
+		ret = -EINVAL;
+		goto clean_pubkey;
+	}
+
+	/* Parse modulus (n) */
+	rsa_key->n_sz = mbedtls_mpi_size(&rsa->N);
+	rsa_key->n = kzalloc(rsa_key->n_sz, GFP_KERNEL);
+	if (!rsa_key->n) {
+		ret = -ENOMEM;
+		goto clean_pubkey;
+	}
+	ret = mbedtls_mpi_write_binary(&rsa->N, (unsigned char *)rsa_key->n,
+				       rsa_key->n_sz);
+	if (ret) {
+		pr_err("Failed to parse modulus (n), ret:-0x%04x\n", -ret);
+		ret = -EINVAL;
+		goto clean_modulus;
+	}
+
+	/* Parse public exponent (e) */
+	rsa_key->e_sz = mbedtls_mpi_size(&rsa->E);
+	rsa_key->e = kzalloc(rsa_key->e_sz, GFP_KERNEL);
+	if (!rsa_key->e) {
+		ret = -ENOMEM;
+		goto clean_modulus;
+	}
+	ret = mbedtls_mpi_write_binary(&rsa->E, (unsigned char *)rsa_key->e,
+				       rsa_key->e_sz);
+	if (!ret)
+		return 0;
+
+	pr_err("Failed to parse public exponent (e), ret:-0x%04x\n", -ret);
+	ret = -EINVAL;
+
+	kfree(rsa_key->e);
+clean_modulus:
+	kfree(rsa_key->n);
+clean_pubkey:
+	mbedtls_pk_free(&pk);
+	return ret;
+}