1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * RSA helper functions using MbedTLS
4 *
5 * Copyright (c) 2024 Linaro Limited
6 * Author: Raymond Mao <raymond.mao@linaro.org>
7 */
8
9 #include <linux/err.h>
10 #include <crypto/internal/rsa.h>
11 #include <library/common.h>
12 #include <mbedtls/pk.h>
13 #include <mbedtls/rsa.h>
14 #include <mbedtls/asn1.h>
15
16 /**
17 * rsa_parse_pub_key() - decodes the BER encoded buffer and stores in the
18 * provided struct rsa_key, pointers to the raw key as is,
19 * so that the caller can copy it or MPI parse it, etc.
20 *
21 * @rsa_key: struct rsa_key key representation
22 * @key: key in BER format
23 * @key_len: length of key
24 *
25 * Return: 0 on success or error code in case of error
26 */
rsa_parse_pub_key(struct rsa_key * rsa_key,const void * key,unsigned int key_len)27 int rsa_parse_pub_key(struct rsa_key *rsa_key, const void *key,
28 unsigned int key_len)
29 {
30 int ret = 0;
31 mbedtls_pk_context pk;
32 mbedtls_rsa_context *rsa;
33
34 mbedtls_pk_init(&pk);
35
36 ret = mbedtls_pk_parse_public_key(&pk, (const unsigned char *)key,
37 key_len);
38 if (ret) {
39 pr_err("Failed to parse public key, ret:-0x%04x\n", -ret);
40 ret = -EINVAL;
41 goto clean_pubkey;
42 }
43
44 /* Ensure that it is a RSA key */
45 if (mbedtls_pk_get_type(&pk) != MBEDTLS_PK_RSA) {
46 pr_err("Non-RSA keys are not supported\n");
47 ret = -EKEYREJECTED;
48 goto clean_pubkey;
49 }
50
51 /* Get RSA key context */
52 rsa = mbedtls_pk_rsa(pk);
53 if (!rsa) {
54 pr_err("Failed to get RSA key context, ret:-0x%04x\n", -ret);
55 ret = -EINVAL;
56 goto clean_pubkey;
57 }
58
59 /* Parse modulus (n) */
60 rsa_key->n_sz = mbedtls_mpi_size(&rsa->N);
61 rsa_key->n = kzalloc(rsa_key->n_sz, GFP_KERNEL);
62 if (!rsa_key->n) {
63 ret = -ENOMEM;
64 goto clean_pubkey;
65 }
66 ret = mbedtls_mpi_write_binary(&rsa->N, (unsigned char *)rsa_key->n,
67 rsa_key->n_sz);
68 if (ret) {
69 pr_err("Failed to parse modulus (n), ret:-0x%04x\n", -ret);
70 ret = -EINVAL;
71 goto clean_modulus;
72 }
73
74 /* Parse public exponent (e) */
75 rsa_key->e_sz = mbedtls_mpi_size(&rsa->E);
76 rsa_key->e = kzalloc(rsa_key->e_sz, GFP_KERNEL);
77 if (!rsa_key->e) {
78 ret = -ENOMEM;
79 goto clean_modulus;
80 }
81 ret = mbedtls_mpi_write_binary(&rsa->E, (unsigned char *)rsa_key->e,
82 rsa_key->e_sz);
83 if (!ret)
84 return 0;
85
86 pr_err("Failed to parse public exponent (e), ret:-0x%04x\n", -ret);
87 ret = -EINVAL;
88
89 kfree(rsa_key->e);
90 clean_modulus:
91 kfree(rsa_key->n);
92 clean_pubkey:
93 mbedtls_pk_free(&pk);
94 return ret;
95 }
96