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 #include <linux/dm-verity-loadpin.h>
22 #include <uapi/linux/loadpin.h>
23 #include <uapi/linux/lsm.h>
24
25 #define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS"
26
27 static void report_load(const char *origin, struct file *file, char *operation)
28 {
29 char *cmdline, *pathname;
30
31 pathname = kstrdup_quotable_file(file, GFP_KERNEL);
32 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
33
34 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
35 origin, operation,
36 (pathname && pathname[0] != '<') ? "\"" : "",
37 pathname,
38 (pathname && pathname[0] != '<') ? "\"" : "",
39 task_pid_nr(current),
40 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
41
42 kfree(cmdline);
43 kfree(pathname);
44 }
45
46 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
47 static char *exclude_read_files[READING_MAX_ID];
48 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
49 static struct super_block *pinned_root;
50 static DEFINE_SPINLOCK(pinned_root_spinlock);
51 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
52 static bool deny_reading_verity_digests;
53 #endif
54
55 #ifdef CONFIG_SYSCTL
56 static struct ctl_table loadpin_sysctl_table[] = {
57 {
58 .procname = "enforce",
59 .data = &enforce,
60 .maxlen = sizeof(int),
61 .mode = 0644,
62 .proc_handler = proc_dointvec_minmax,
63 .extra1 = SYSCTL_ONE,
64 .extra2 = SYSCTL_ONE,
65 },
66 };
67
68 static void set_sysctl(bool is_writable)
69 {
70 /*
71 * If load pinning is not enforced via a read-only block
72 * device, allow sysctl to change modes for testing.
73 */
74 if (is_writable)
75 loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
76 else
77 loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
78 }
79 #else
80 static inline void set_sysctl(bool is_writable) { }
81 #endif
82
83 static void report_writable(struct super_block *mnt_sb, bool writable)
84 {
85 if (mnt_sb->s_bdev) {
86 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
87 MAJOR(mnt_sb->s_bdev->bd_dev),
88 MINOR(mnt_sb->s_bdev->bd_dev),
89 writable ? "writable" : "read-only");
90 } else
91 pr_info("mnt_sb lacks block device, treating as: writable\n");
92
93 if (!writable)
94 pr_info("load pinning engaged.\n");
95 }
96
97 /*
98 * This must be called after early kernel init, since then the rootdev
99 * is available.
100 */
101 static bool sb_is_writable(struct super_block *mnt_sb)
102 {
103 bool writable = true;
104
105 if (mnt_sb->s_bdev)
106 writable = !bdev_read_only(mnt_sb->s_bdev);
107
108 return writable;
109 }
110
111 static void loadpin_sb_free_security(struct super_block *mnt_sb)
112 {
113 /*
114 * When unmounting the filesystem we were using for load
115 * pinning, we acknowledge the superblock release, but make sure
116 * no other modules or firmware can be loaded when we are in
117 * enforcing mode. Otherwise, allow the root to be reestablished.
118 */
119 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
120 if (enforce) {
121 pinned_root = ERR_PTR(-EIO);
122 pr_info("umount pinned fs: refusing further loads\n");
123 } else {
124 pinned_root = NULL;
125 }
126 }
127 }
128
129 static int loadpin_check(struct file *file, enum kernel_read_file_id id)
130 {
131 struct super_block *load_root;
132 const char *origin = kernel_read_file_id_str(id);
133 bool first_root_pin = false;
134 bool load_root_writable;
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 load_root_writable = sb_is_writable(load_root);
156
157 /* First loaded module/firmware defines the root for all others. */
158 spin_lock(&pinned_root_spinlock);
159 /*
160 * pinned_root is only NULL at startup or when the pinned root has
161 * been unmounted while we are not in enforcing mode. Otherwise, it
162 * is either a valid reference, or an ERR_PTR.
163 */
164 if (!pinned_root) {
165 pinned_root = load_root;
166 first_root_pin = true;
167 }
168 spin_unlock(&pinned_root_spinlock);
169
170 if (first_root_pin) {
171 report_writable(pinned_root, load_root_writable);
172 set_sysctl(load_root_writable);
173 report_load(origin, file, "pinned");
174 }
175
176 if (IS_ERR_OR_NULL(pinned_root) ||
177 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
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
190 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
191 bool contents)
192 {
193 /*
194 * LoadPin only cares about the _origin_ of a file, not its
195 * contents, so we can ignore the "are full contents available"
196 * argument here.
197 */
198 return loadpin_check(file, id);
199 }
200
201 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
202 {
203 /*
204 * LoadPin only cares about the _origin_ of a file, not its
205 * contents, so a NULL file is passed, and we can ignore the
206 * state of "contents".
207 */
208 return loadpin_check(NULL, (enum kernel_read_file_id) id);
209 }
210
211 static const struct lsm_id loadpin_lsmid = {
212 .name = "loadpin",
213 .id = LSM_ID_LOADPIN,
214 };
215
216 static struct security_hook_list loadpin_hooks[] __ro_after_init = {
217 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
218 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
219 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
220 };
221
222 static void __init parse_exclude(void)
223 {
224 int i, j;
225 char *cur;
226
227 /*
228 * Make sure all the arrays stay within expected sizes. This
229 * is slightly weird because kernel_read_file_str[] includes
230 * READING_MAX_ID, which isn't actually meaningful here.
231 */
232 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
233 ARRAY_SIZE(ignore_read_file_id));
234 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
235 ARRAY_SIZE(ignore_read_file_id));
236
237 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
238 cur = exclude_read_files[i];
239 if (!cur)
240 break;
241 if (*cur == '\0')
242 continue;
243
244 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
245 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
246 pr_info("excluding: %s\n",
247 kernel_read_file_str[j]);
248 ignore_read_file_id[j] = 1;
249 /*
250 * Can not break, because one read_file_str
251 * may map to more than on read_file_id.
252 */
253 }
254 }
255 }
256 }
257
258 static int __init loadpin_init(void)
259 {
260 pr_info("ready to pin (currently %senforcing)\n",
261 enforce ? "" : "not ");
262 parse_exclude();
263 #ifdef CONFIG_SYSCTL
264 if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
265 pr_notice("sysctl registration failed!\n");
266 #endif
267 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
268 &loadpin_lsmid);
269
270 return 0;
271 }
272
273 DEFINE_LSM(loadpin) = {
274 .name = "loadpin",
275 .init = loadpin_init,
276 };
277
278 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
279
280 enum loadpin_securityfs_interface_index {
281 LOADPIN_DM_VERITY,
282 };
283
284 static int read_trusted_verity_root_digests(unsigned int fd)
285 {
286 struct fd f;
287 void *data;
288 int rc;
289 char *p, *d;
290
291 if (deny_reading_verity_digests)
292 return -EPERM;
293
294 /* The list of trusted root digests can only be set up once */
295 if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
296 return -EPERM;
297
298 f = fdget(fd);
299 if (!f.file)
300 return -EINVAL;
301
302 data = kzalloc(SZ_4K, GFP_KERNEL);
303 if (!data) {
304 rc = -ENOMEM;
305 goto err;
306 }
307
308 rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
309 if (rc < 0)
310 goto err;
311
312 p = data;
313 p[rc] = '\0';
314 p = strim(p);
315
316 p = strim(data);
317 while ((d = strsep(&p, "\n")) != NULL) {
318 int len;
319 struct dm_verity_loadpin_trusted_root_digest *trd;
320
321 if (d == data) {
322 /* first line, validate header */
323 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
324 rc = -EPROTO;
325 goto err;
326 }
327
328 continue;
329 }
330
331 len = strlen(d);
332
333 if (len % 2) {
334 rc = -EPROTO;
335 goto err;
336 }
337
338 len /= 2;
339
340 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
341 if (!trd) {
342 rc = -ENOMEM;
343 goto err;
344 }
345 trd->len = len;
346
347 if (hex2bin(trd->data, d, len)) {
348 kfree(trd);
349 rc = -EPROTO;
350 goto err;
351 }
352
353 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
354 }
355
356 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
357 rc = -EPROTO;
358 goto err;
359 }
360
361 kfree(data);
362 fdput(f);
363
364 return 0;
365
366 err:
367 kfree(data);
368
369 /* any failure in loading/parsing invalidates the entire list */
370 {
371 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
372
373 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
374 list_del(&trd->node);
375 kfree(trd);
376 }
377 }
378
379 /* disallow further attempts after reading a corrupt/invalid file */
380 deny_reading_verity_digests = true;
381
382 fdput(f);
383
384 return rc;
385 }
386
387 /******************************** securityfs ********************************/
388
389 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
390 {
391 void __user *uarg = (void __user *)arg;
392 unsigned int fd;
393
394 switch (cmd) {
395 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
396 if (copy_from_user(&fd, uarg, sizeof(fd)))
397 return -EFAULT;
398
399 return read_trusted_verity_root_digests(fd);
400
401 default:
402 return -EINVAL;
403 }
404 }
405
406 static const struct file_operations loadpin_dm_verity_ops = {
407 .unlocked_ioctl = dm_verity_ioctl,
408 .compat_ioctl = compat_ptr_ioctl,
409 };
410
411 /**
412 * init_loadpin_securityfs - create the securityfs directory for LoadPin
413 *
414 * We can not put this method normally under the loadpin_init() code path since
415 * the security subsystem gets initialized before the vfs caches.
416 *
417 * Returns 0 if the securityfs directory creation was successful.
418 */
419 static int __init init_loadpin_securityfs(void)
420 {
421 struct dentry *loadpin_dir, *dentry;
422
423 loadpin_dir = securityfs_create_dir("loadpin", NULL);
424 if (IS_ERR(loadpin_dir)) {
425 pr_err("LoadPin: could not create securityfs dir: %ld\n",
426 PTR_ERR(loadpin_dir));
427 return PTR_ERR(loadpin_dir);
428 }
429
430 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
431 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
432 if (IS_ERR(dentry)) {
433 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
434 PTR_ERR(dentry));
435 return PTR_ERR(dentry);
436 }
437
438 return 0;
439 }
440
441 fs_initcall(init_loadpin_securityfs);
442
443 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */
444
445 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
446 module_param(enforce, int, 0);
447 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
448 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
449 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
450
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