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_hook_supports_modsig - can the policy allow modsig for this hook?
37 *
38 * modsig is only supported by hooks using ima_post_read_file(), because only
39 * they preload the contents of the file in a buffer. FILE_CHECK does that in
40 * some cases, but not when reached from vfs_open(). POLICY_CHECK can support
41 * it, but it's not useful in practice because it's a text file so deny.
42 */
ima_hook_supports_modsig(enum ima_hooks func)43 bool ima_hook_supports_modsig(enum ima_hooks func)
44 {
45 switch (func) {
46 case KEXEC_KERNEL_CHECK:
47 case KEXEC_INITRAMFS_CHECK:
48 case MODULE_CHECK:
49 return true;
50 default:
51 return false;
52 }
53 }
54
55 /*
56 * ima_read_modsig - Read modsig from buf.
57 *
58 * Return: 0 on success, error code otherwise.
59 */
ima_read_modsig(enum ima_hooks func,const void * buf,loff_t buf_len,struct modsig ** modsig)60 int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
61 struct modsig **modsig)
62 {
63 const size_t marker_len = strlen(MODULE_SIG_STRING);
64 const struct module_signature *sig;
65 struct modsig *hdr;
66 size_t sig_len;
67 const void *p;
68 int rc;
69
70 if (buf_len <= marker_len + sizeof(*sig))
71 return -ENOENT;
72
73 p = buf + buf_len - marker_len;
74 if (memcmp(p, MODULE_SIG_STRING, marker_len))
75 return -ENOENT;
76
77 buf_len -= marker_len;
78 sig = (const struct module_signature *)(p - sizeof(*sig));
79
80 rc = mod_check_sig(sig, buf_len, func_tokens[func]);
81 if (rc)
82 return rc;
83
84 sig_len = be32_to_cpu(sig->sig_len);
85 buf_len -= sig_len + sizeof(*sig);
86
87 /* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
88 hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
89 if (!hdr)
90 return -ENOMEM;
91
92 hdr->pkcs7_msg = pkcs7_parse_message(buf + buf_len, sig_len);
93 if (IS_ERR(hdr->pkcs7_msg)) {
94 rc = PTR_ERR(hdr->pkcs7_msg);
95 kfree(hdr);
96 return rc;
97 }
98
99 memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
100 hdr->raw_pkcs7_len = sig_len;
101
102 /* We don't know the hash algorithm yet. */
103 hdr->hash_algo = HASH_ALGO__LAST;
104
105 *modsig = hdr;
106
107 return 0;
108 }
109
110 /**
111 * ima_collect_modsig - Calculate the file hash without the appended signature.
112 *
113 * Since the modsig is part of the file contents, the hash used in its signature
114 * isn't the same one ordinarily calculated by IMA. Therefore PKCS7 code
115 * calculates a separate one for signature verification.
116 */
ima_collect_modsig(struct modsig * modsig,const void * buf,loff_t size)117 void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size)
118 {
119 int rc;
120
121 /*
122 * Provide the file contents (minus the appended sig) so that the PKCS7
123 * code can calculate the file hash.
124 */
125 size -= modsig->raw_pkcs7_len + strlen(MODULE_SIG_STRING) +
126 sizeof(struct module_signature);
127 rc = pkcs7_supply_detached_data(modsig->pkcs7_msg, buf, size);
128 if (rc)
129 return;
130
131 /* Ask the PKCS7 code to calculate the file hash. */
132 rc = pkcs7_get_digest(modsig->pkcs7_msg, &modsig->digest,
133 &modsig->digest_size, &modsig->hash_algo);
134 }
135
ima_modsig_verify(struct key * keyring,const struct modsig * modsig)136 int ima_modsig_verify(struct key *keyring, const struct modsig *modsig)
137 {
138 return verify_pkcs7_message_sig(NULL, 0, modsig->pkcs7_msg, keyring,
139 VERIFYING_MODULE_SIGNATURE, NULL, NULL);
140 }
141
ima_get_modsig_digest(const struct modsig * modsig,enum hash_algo * algo,const u8 ** digest,u32 * digest_size)142 int ima_get_modsig_digest(const struct modsig *modsig, enum hash_algo *algo,
143 const u8 **digest, u32 *digest_size)
144 {
145 *algo = modsig->hash_algo;
146 *digest = modsig->digest;
147 *digest_size = modsig->digest_size;
148
149 return 0;
150 }
151
ima_get_raw_modsig(const struct modsig * modsig,const void ** data,u32 * data_len)152 int ima_get_raw_modsig(const struct modsig *modsig, const void **data,
153 u32 *data_len)
154 {
155 *data = &modsig->raw_pkcs7;
156 *data_len = modsig->raw_pkcs7_len;
157
158 return 0;
159 }
160
ima_free_modsig(struct modsig * modsig)161 void ima_free_modsig(struct modsig *modsig)
162 {
163 if (!modsig)
164 return;
165
166 pkcs7_free_message(modsig->pkcs7_msg);
167 kfree(modsig);
168 }
169
