1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* Module signature checker
3 *
4 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
5 * Written by David Howells (dhowells@redhat.com)
6 */
7
8 #include <linux/kernel.h>
9 #include <linux/errno.h>
10 #include <linux/module.h>
11 #include <linux/module_signature.h>
12 #include <linux/string.h>
13 #include <linux/verification.h>
14 #include <linux/security.h>
15 #include <crypto/public_key.h>
16 #include <uapi/linux/module.h>
17 #include "internal.h"
18
19 #undef MODULE_PARAM_PREFIX
20 #define MODULE_PARAM_PREFIX "module."
21
22 static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
23 module_param(sig_enforce, bool_enable_only, 0644);
24
25 /*
26 * Export sig_enforce kernel cmdline parameter to allow other subsystems rely
27 * on that instead of directly to CONFIG_MODULE_SIG_FORCE config.
28 */
is_module_sig_enforced(void)29 bool is_module_sig_enforced(void)
30 {
31 return sig_enforce;
32 }
33 EXPORT_SYMBOL(is_module_sig_enforced);
34
set_module_sig_enforced(void)35 void set_module_sig_enforced(void)
36 {
37 sig_enforce = true;
38 }
39
40 /*
41 * Verify the signature on a module.
42 */
mod_verify_sig(const void * mod,struct load_info * info)43 int mod_verify_sig(const void *mod, struct load_info *info)
44 {
45 struct module_signature ms;
46 size_t sig_len, modlen = info->len;
47 int ret;
48
49 pr_devel("==>%s(,%zu)\n", __func__, modlen);
50
51 if (modlen <= sizeof(ms))
52 return -EBADMSG;
53
54 memcpy(&ms, mod + (modlen - sizeof(ms)), sizeof(ms));
55
56 ret = mod_check_sig(&ms, modlen, "module");
57 if (ret)
58 return ret;
59
60 sig_len = be32_to_cpu(ms.sig_len);
61 modlen -= sig_len + sizeof(ms);
62 info->len = modlen;
63
64 return verify_pkcs7_signature(mod, modlen, mod + modlen, sig_len,
65 VERIFY_USE_SECONDARY_KEYRING,
66 VERIFYING_MODULE_SIGNATURE,
67 NULL, NULL);
68 }
69
module_sig_check(struct load_info * info,int flags)70 int module_sig_check(struct load_info *info, int flags)
71 {
72 int err = -ENODATA;
73 const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
74 const char *reason;
75 const void *mod = info->hdr;
76 bool mangled_module = flags & (MODULE_INIT_IGNORE_MODVERSIONS |
77 MODULE_INIT_IGNORE_VERMAGIC);
78 /*
79 * Do not allow mangled modules as a module with version information
80 * removed is no longer the module that was signed.
81 */
82 if (!mangled_module &&
83 info->len > markerlen &&
84 memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
85 /* We truncate the module to discard the signature */
86 info->len -= markerlen;
87 err = mod_verify_sig(mod, info);
88 if (!err) {
89 info->sig_ok = true;
90 return 0;
91 }
92 }
93
94 /*
95 * We don't permit modules to be loaded into the trusted kernels
96 * without a valid signature on them, but if we're not enforcing,
97 * certain errors are non-fatal.
98 */
99 switch (err) {
100 case -ENODATA:
101 reason = "unsigned module";
102 break;
103 case -ENOPKG:
104 reason = "module with unsupported crypto";
105 break;
106 case -ENOKEY:
107 reason = "module with unavailable key";
108 break;
109
110 default:
111 /*
112 * All other errors are fatal, including lack of memory,
113 * unparseable signatures, and signature check failures --
114 * even if signatures aren't required.
115 */
116 return err;
117 }
118
119 if (is_module_sig_enforced()) {
120 pr_notice("Loading of %s is rejected\n", reason);
121 return -EKEYREJECTED;
122 }
123
124 return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
125 }
126