1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Module and Firmware Pinning Security Module
4 *
5 * Copyright 2011-2016 Google Inc.
6 *
7 * Author: Kees Cook <keescook@chromium.org>
8 */
9
10 #define pr_fmt(fmt) "LoadPin: " fmt
11
12 #include <linux/module.h>
13 #include <linux/fs.h>
14 #include <linux/kernel_read_file.h>
15 #include <linux/lsm_hooks.h>
16 #include <linux/mount.h>
17 #include <linux/blkdev.h>
18 #include <linux/path.h>
19 #include <linux/sched.h> /* current */
20 #include <linux/string_helpers.h>
21
report_load(const char * origin,struct file * file,char * operation)22 static void report_load(const char *origin, struct file *file, char *operation)
23 {
24 char *cmdline, *pathname;
25
26 pathname = kstrdup_quotable_file(file, GFP_KERNEL);
27 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
28
29 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
30 origin, operation,
31 (pathname && pathname[0] != '<') ? "\"" : "",
32 pathname,
33 (pathname && pathname[0] != '<') ? "\"" : "",
34 task_pid_nr(current),
35 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
36
37 kfree(cmdline);
38 kfree(pathname);
39 }
40
41 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
42 static char *exclude_read_files[READING_MAX_ID];
43 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
44 static struct super_block *pinned_root;
45 static DEFINE_SPINLOCK(pinned_root_spinlock);
46
47 #ifdef CONFIG_SYSCTL
48
49 static struct ctl_path loadpin_sysctl_path[] = {
50 { .procname = "kernel", },
51 { .procname = "loadpin", },
52 { }
53 };
54
55 static struct ctl_table loadpin_sysctl_table[] = {
56 {
57 .procname = "enforce",
58 .data = &enforce,
59 .maxlen = sizeof(int),
60 .mode = 0644,
61 .proc_handler = proc_dointvec_minmax,
62 .extra1 = SYSCTL_ZERO,
63 .extra2 = SYSCTL_ONE,
64 },
65 { }
66 };
67
68 /*
69 * This must be called after early kernel init, since then the rootdev
70 * is available.
71 */
check_pinning_enforcement(struct super_block * mnt_sb)72 static void check_pinning_enforcement(struct super_block *mnt_sb)
73 {
74 bool ro = false;
75
76 /*
77 * If load pinning is not enforced via a read-only block
78 * device, allow sysctl to change modes for testing.
79 */
80 if (mnt_sb->s_bdev) {
81 char bdev[BDEVNAME_SIZE];
82
83 ro = bdev_read_only(mnt_sb->s_bdev);
84 bdevname(mnt_sb->s_bdev, bdev);
85 pr_info("%s (%u:%u): %s\n", bdev,
86 MAJOR(mnt_sb->s_bdev->bd_dev),
87 MINOR(mnt_sb->s_bdev->bd_dev),
88 ro ? "read-only" : "writable");
89 } else
90 pr_info("mnt_sb lacks block device, treating as: writable\n");
91
92 if (!ro) {
93 if (!register_sysctl_paths(loadpin_sysctl_path,
94 loadpin_sysctl_table))
95 pr_notice("sysctl registration failed!\n");
96 else
97 pr_info("enforcement can be disabled.\n");
98 } else
99 pr_info("load pinning engaged.\n");
100 }
101 #else
check_pinning_enforcement(struct super_block * mnt_sb)102 static void check_pinning_enforcement(struct super_block *mnt_sb)
103 {
104 pr_info("load pinning engaged.\n");
105 }
106 #endif
107
loadpin_sb_free_security(struct super_block * mnt_sb)108 static void loadpin_sb_free_security(struct super_block *mnt_sb)
109 {
110 /*
111 * When unmounting the filesystem we were using for load
112 * pinning, we acknowledge the superblock release, but make sure
113 * no other modules or firmware can be loaded.
114 */
115 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
116 pinned_root = ERR_PTR(-EIO);
117 pr_info("umount pinned fs: refusing further loads\n");
118 }
119 }
120
loadpin_read_file(struct file * file,enum kernel_read_file_id id,bool contents)121 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
122 bool contents)
123 {
124 struct super_block *load_root;
125 const char *origin = kernel_read_file_id_str(id);
126
127 /*
128 * If we will not know that we'll be seeing the full contents
129 * then we cannot trust a load will be complete and unchanged
130 * off disk. Treat all contents=false hooks as if there were
131 * no associated file struct.
132 */
133 if (!contents)
134 file = NULL;
135
136 /* If the file id is excluded, ignore the pinning. */
137 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
138 ignore_read_file_id[id]) {
139 report_load(origin, file, "pinning-excluded");
140 return 0;
141 }
142
143 /* This handles the older init_module API that has a NULL file. */
144 if (!file) {
145 if (!enforce) {
146 report_load(origin, NULL, "old-api-pinning-ignored");
147 return 0;
148 }
149
150 report_load(origin, NULL, "old-api-denied");
151 return -EPERM;
152 }
153
154 load_root = file->f_path.mnt->mnt_sb;
155
156 /* First loaded module/firmware defines the root for all others. */
157 spin_lock(&pinned_root_spinlock);
158 /*
159 * pinned_root is only NULL at startup. Otherwise, it is either
160 * a valid reference, or an ERR_PTR.
161 */
162 if (!pinned_root) {
163 pinned_root = load_root;
164 /*
165 * Unlock now since it's only pinned_root we care about.
166 * In the worst case, we will (correctly) report pinning
167 * failures before we have announced that pinning is
168 * enforcing. This would be purely cosmetic.
169 */
170 spin_unlock(&pinned_root_spinlock);
171 check_pinning_enforcement(pinned_root);
172 report_load(origin, file, "pinned");
173 } else {
174 spin_unlock(&pinned_root_spinlock);
175 }
176
177 if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
178 if (unlikely(!enforce)) {
179 report_load(origin, file, "pinning-ignored");
180 return 0;
181 }
182
183 report_load(origin, file, "denied");
184 return -EPERM;
185 }
186
187 return 0;
188 }
189
loadpin_load_data(enum kernel_load_data_id id,bool contents)190 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
191 {
192 return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
193 }
194
195 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
196 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
197 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
198 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
199 };
200
parse_exclude(void)201 static void __init parse_exclude(void)
202 {
203 int i, j;
204 char *cur;
205
206 /*
207 * Make sure all the arrays stay within expected sizes. This
208 * is slightly weird because kernel_read_file_str[] includes
209 * READING_MAX_ID, which isn't actually meaningful here.
210 */
211 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
212 ARRAY_SIZE(ignore_read_file_id));
213 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
214 ARRAY_SIZE(ignore_read_file_id));
215
216 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
217 cur = exclude_read_files[i];
218 if (!cur)
219 break;
220 if (*cur == '\0')
221 continue;
222
223 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
224 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
225 pr_info("excluding: %s\n",
226 kernel_read_file_str[j]);
227 ignore_read_file_id[j] = 1;
228 /*
229 * Can not break, because one read_file_str
230 * may map to more than on read_file_id.
231 */
232 }
233 }
234 }
235 }
236
loadpin_init(void)237 static int __init loadpin_init(void)
238 {
239 pr_info("ready to pin (currently %senforcing)\n",
240 enforce ? "" : "not ");
241 parse_exclude();
242 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
243 return 0;
244 }
245
246 DEFINE_LSM(loadpin) = {
247 .name = "loadpin",
248 .init = loadpin_init,
249 };
250
251 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
252 module_param(enforce, int, 0);
253 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
254 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
255 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
256