1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * Public key helper functions using MbedTLS X509 library
4 *
5 * Copyright (c) 2024 Linaro Limited
6 * Author: Raymond Mao <raymond.mao@linaro.org>
7 */
8
9 #include <linux/compat.h>
10 #include <crypto/public_key.h>
11
public_key_verify_signature(const struct public_key * pkey,const struct public_key_signature * sig)12 int public_key_verify_signature(const struct public_key *pkey,
13 const struct public_key_signature *sig)
14 {
15 mbedtls_md_type_t mb_hash_algo;
16 mbedtls_pk_context pk_ctx;
17 int ret;
18
19 if (!pkey || !sig || pkey->key_is_private)
20 return -EINVAL;
21
22 /*
23 * ECRDSA (Elliptic Curve Russian Digital Signature Algorithm) is not
24 * supported by MbedTLS.
25 */
26 if (strcmp(pkey->pkey_algo, "rsa")) {
27 pr_err("Encryption is not RSA: %s\n", sig->pkey_algo);
28 return -EINVAL;
29 }
30
31 /*
32 * Can be pkcs1 or raw, but pkcs1 is expected.
33 * This is just for argument checking, not necessarily passed to MbedTLS,
34 * For RSA signatures, MbedTLS typically supports the PKCS#1 v1.5
35 * (aka. pkcs1) encoding by default.
36 * The library internally handles the details of decoding and verifying
37 * the signature according to the expected encoding for the specified algorithm.
38 */
39 if (strcmp(sig->encoding, "pkcs1")) {
40 pr_err("Encoding %s is not supported, only supports pkcs1\n",
41 sig->encoding);
42 return -EINVAL;
43 }
44
45 if (!strcmp(sig->hash_algo, "sha1"))
46 mb_hash_algo = MBEDTLS_MD_SHA1;
47 else if (!strcmp(sig->hash_algo, "sha224"))
48 mb_hash_algo = MBEDTLS_MD_SHA224;
49 else if (!strcmp(sig->hash_algo, "sha256"))
50 mb_hash_algo = MBEDTLS_MD_SHA256;
51 else if (!strcmp(sig->hash_algo, "sha384"))
52 mb_hash_algo = MBEDTLS_MD_SHA384;
53 else if (!strcmp(sig->hash_algo, "sha512"))
54 mb_hash_algo = MBEDTLS_MD_SHA512;
55 else /* Unknown or unsupported hash algorithm */
56 return -EINVAL;
57 /* Initialize the mbedtls_pk_context with RSA key type */
58 mbedtls_pk_init(&pk_ctx);
59
60 /* Parse the DER-encoded public key */
61 ret = mbedtls_pk_parse_public_key(&pk_ctx, pkey->key, pkey->keylen);
62 if (ret) {
63 pr_err("Failed to parse public key, ret:-0x%04x\n", -ret);
64 ret = -EINVAL;
65 goto err_key;
66 }
67
68 /* Ensure that it is a RSA key */
69 if (mbedtls_pk_get_type(&pk_ctx) != MBEDTLS_PK_RSA) {
70 pr_err("Only RSA keys are supported\n");
71 ret = -EKEYREJECTED;
72 goto err_key;
73 }
74
75 /* Verify the hash */
76 ret = mbedtls_pk_verify(&pk_ctx, mb_hash_algo, sig->digest,
77 sig->digest_size, sig->s, sig->s_size);
78
79 err_key:
80 mbedtls_pk_free(&pk_ctx);
81 return ret;
82 }
83