1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3 * IMA support for appraising module-style appended signatures.
4 *
5 * Copyright (C) 2019 IBM Corporation
6 *
7 * Author:
8 * Thiago Jung Bauermann <bauerman@linux.ibm.com>
9 */
10
11 #include <linux/types.h>
12 #include <linux/module_signature.h>
13 #include <keys/asymmetric-type.h>
14 #include <crypto/pkcs7.h>
15
16 #include "ima.h"
17
18 struct modsig {
19 struct pkcs7_message *pkcs7_msg;
20
21 enum hash_algo hash_algo;
22
23 /* This digest will go in the 'd-modsig' field of the IMA template. */
24 const u8 *digest;
25 u32 digest_size;
26
27 /*
28 * This is what will go to the measurement list if the template requires
29 * storing the signature.
30 */
31 int raw_pkcs7_len;
32 u8 raw_pkcs7[];
33 };
34
35 /*
36 * ima_read_modsig - Read modsig from buf.
37 *
38 * Return: 0 on success, error code otherwise.
39 */
ima_read_modsig(enum ima_hooks func,const void * buf,loff_t buf_len,struct modsig ** modsig)40 int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
41 struct modsig **modsig)
42 {
43 const size_t marker_len = strlen(MODULE_SIG_STRING);
44 const struct module_signature *sig;
45 struct modsig *hdr;
46 size_t sig_len;
47 const void *p;
48 int rc;
49
50 if (buf_len <= marker_len + sizeof(*sig))
51 return -ENOENT;
52
53 p = buf + buf_len - marker_len;
54 if (memcmp(p, MODULE_SIG_STRING, marker_len))
55 return -ENOENT;
56
57 buf_len -= marker_len;
58 sig = (const struct module_signature *)(p - sizeof(*sig));
59
60 rc = mod_check_sig(sig, buf_len, func_tokens[func]);
61 if (rc)
62 return rc;
63
64 sig_len = be32_to_cpu(sig->sig_len);
65 buf_len -= sig_len + sizeof(*sig);
66
67 /* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
68 hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
69 if (!hdr)
70 return -ENOMEM;
71
72 hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
73 if (IS_ERR(hdr->pkcs7_msg)) {
74 rc = PTR_ERR(hdr->pkcs7_msg);
75 kfree(hdr);
76 return rc;
77 }
78
79 memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
80 hdr->raw_pkcs7_len = sig_len;
81
82 /* We don't know the hash algorithm yet. */
83 hdr->hash_algo = HASH_ALGO__LAST;
84
85 *modsig = hdr;
86
87 return 0;
88 }
89
90 /**
91 * ima_collect_modsig - Calculate the file hash without the appended signature.
92 * @modsig: parsed module signature
93 * @buf: data to verify the signature on
94 * @size: data size
95 *
96 * Since the modsig is part of the file contents, the hash used in its signature
97 * isn't the same one ordinarily calculated by IMA. Therefore PKCS7 code
98 * calculates a separate one for signature verification.
99 */
ima_collect_modsig(struct modsig * modsig,const void * buf,loff_t size)100 void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size)
101 {
102 int rc;
103
104 /*
105 * Provide the file contents (minus the appended sig) so that the PKCS7
106 * code can calculate the file hash.
107 */
108 size -= modsig->raw_pkcs7_len + strlen(MODULE_SIG_STRING) +
109 sizeof(struct module_signature);
110 rc = pkcs7_supply_detached_data(modsig->pkcs7_msg, buf, size);
111 if (rc)
112 return;
113
114 /* Ask the PKCS7 code to calculate the file hash. */
115 rc = pkcs7_get_digest(modsig->pkcs7_msg, &modsig->digest,
116 &modsig->digest_size, &modsig->hash_algo);
117 }
118
ima_modsig_verify(struct key * keyring,const struct modsig * modsig)119 int ima_modsig_verify(struct key *keyring, const struct modsig *modsig)
120 {
121 return verify_pkcs7_message_sig(NULL, 0, modsig->pkcs7_msg, keyring,
122 VERIFYING_MODULE_SIGNATURE, NULL, NULL);
123 }
124
ima_get_modsig_digest(const struct modsig * modsig,enum hash_algo * algo,const u8 ** digest,u32 * digest_size)125 int ima_get_modsig_digest(const struct modsig *modsig, enum hash_algo *algo,
126 const u8 **digest, u32 *digest_size)
127 {
128 *algo = modsig->hash_algo;
129 *digest = modsig->digest;
130 *digest_size = modsig->digest_size;
131
132 return 0;
133 }
134
ima_get_raw_modsig(const struct modsig * modsig,const void ** data,u32 * data_len)135 int ima_get_raw_modsig(const struct modsig *modsig, const void **data,
136 u32 *data_len)
137 {
138 *data = &modsig->raw_pkcs7;
139 *data_len = modsig->raw_pkcs7_len;
140
141 return 0;
142 }
143
ima_free_modsig(struct modsig * modsig)144 void ima_free_modsig(struct modsig *modsig)
145 {
146 if (!modsig)
147 return;
148
149 pkcs7_free_message(modsig->pkcs7_msg);
150 kfree(modsig);
151 }
152
