xref: /openbmc/linux/kernel/module/signing.c (revision 73503963)
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