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
report_load(const char * origin,struct file * file,char * operation)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
set_sysctl(bool is_writable)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
set_sysctl(bool is_writable)80 static inline void set_sysctl(bool is_writable) { }
81 #endif
82
report_writable(struct super_block * mnt_sb,bool writable)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 */
sb_is_writable(struct super_block * mnt_sb)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
loadpin_sb_free_security(struct super_block * mnt_sb)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
loadpin_check(struct file * file,enum kernel_read_file_id id)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
loadpin_read_file(struct file * file,enum kernel_read_file_id id,bool contents)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
loadpin_load_data(enum kernel_load_data_id id,bool contents)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
parse_exclude(void)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
loadpin_init(void)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
read_trusted_verity_root_digests(unsigned int fd)284 static int read_trusted_verity_root_digests(unsigned int fd)
285 {
286 void *data;
287 int rc;
288 char *p, *d;
289
290 if (deny_reading_verity_digests)
291 return -EPERM;
292
293 /* The list of trusted root digests can only be set up once */
294 if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
295 return -EPERM;
296
297 CLASS(fd, f)(fd);
298 if (fd_empty(f))
299 return -EINVAL;
300
301 data = kzalloc(SZ_4K, GFP_KERNEL);
302 if (!data) {
303 rc = -ENOMEM;
304 goto err;
305 }
306
307 rc = kernel_read_file(fd_file(f), 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
308 if (rc < 0)
309 goto err;
310
311 p = data;
312 p[rc] = '\0';
313 p = strim(p);
314
315 p = strim(data);
316 while ((d = strsep(&p, "\n")) != NULL) {
317 int len;
318 struct dm_verity_loadpin_trusted_root_digest *trd;
319
320 if (d == data) {
321 /* first line, validate header */
322 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
323 rc = -EPROTO;
324 goto err;
325 }
326
327 continue;
328 }
329
330 len = strlen(d);
331
332 if (len % 2) {
333 rc = -EPROTO;
334 goto err;
335 }
336
337 len /= 2;
338
339 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
340 if (!trd) {
341 rc = -ENOMEM;
342 goto err;
343 }
344 trd->len = len;
345
346 if (hex2bin(trd->data, d, len)) {
347 kfree(trd);
348 rc = -EPROTO;
349 goto err;
350 }
351
352 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
353 }
354
355 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
356 rc = -EPROTO;
357 goto err;
358 }
359
360 kfree(data);
361
362 return 0;
363
364 err:
365 kfree(data);
366
367 /* any failure in loading/parsing invalidates the entire list */
368 {
369 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
370
371 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
372 list_del(&trd->node);
373 kfree(trd);
374 }
375 }
376
377 /* disallow further attempts after reading a corrupt/invalid file */
378 deny_reading_verity_digests = true;
379
380 return rc;
381 }
382
383 /******************************** securityfs ********************************/
384
dm_verity_ioctl(struct file * filp,unsigned int cmd,unsigned long arg)385 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
386 {
387 void __user *uarg = (void __user *)arg;
388 unsigned int fd;
389
390 switch (cmd) {
391 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
392 if (copy_from_user(&fd, uarg, sizeof(fd)))
393 return -EFAULT;
394
395 return read_trusted_verity_root_digests(fd);
396
397 default:
398 return -EINVAL;
399 }
400 }
401
402 static const struct file_operations loadpin_dm_verity_ops = {
403 .unlocked_ioctl = dm_verity_ioctl,
404 .compat_ioctl = compat_ptr_ioctl,
405 };
406
407 /**
408 * init_loadpin_securityfs - create the securityfs directory for LoadPin
409 *
410 * We can not put this method normally under the loadpin_init() code path since
411 * the security subsystem gets initialized before the vfs caches.
412 *
413 * Returns 0 if the securityfs directory creation was successful.
414 */
init_loadpin_securityfs(void)415 static int __init init_loadpin_securityfs(void)
416 {
417 struct dentry *loadpin_dir, *dentry;
418
419 loadpin_dir = securityfs_create_dir("loadpin", NULL);
420 if (IS_ERR(loadpin_dir)) {
421 pr_err("LoadPin: could not create securityfs dir: %ld\n",
422 PTR_ERR(loadpin_dir));
423 return PTR_ERR(loadpin_dir);
424 }
425
426 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
427 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
428 if (IS_ERR(dentry)) {
429 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
430 PTR_ERR(dentry));
431 return PTR_ERR(dentry);
432 }
433
434 return 0;
435 }
436
437 fs_initcall(init_loadpin_securityfs);
438
439 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */
440
441 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
442 module_param(enforce, int, 0);
443 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
444 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
445 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
446