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
27static 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(objp: cmdline);
43 kfree(objp: pathname);
44}
45
46static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
47static char *exclude_read_files[READING_MAX_ID];
48static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
49static struct super_block *pinned_root;
50static DEFINE_SPINLOCK(pinned_root_spinlock);
51#ifdef CONFIG_SECURITY_LOADPIN_VERITY
52static bool deny_reading_verity_digests;
53#endif
54
55#ifdef CONFIG_SYSCTL
56static 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
68static 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
80static inline void set_sysctl(bool is_writable) { }
81#endif
82
83static 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 */
101static 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(bdev: mnt_sb->s_bdev);
107
108 return writable;
109}
110
111static 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(ptr: pinned_root) && mnt_sb == pinned_root) {
120 if (enforce) {
121 pinned_root = ERR_PTR(error: -EIO);
122 pr_info("umount pinned fs: refusing further loads\n");
123 } else {
124 pinned_root = NULL;
125 }
126 }
127}
128
129static 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, operation: "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, operation: "old-api-pinning-ignored");
147 return 0;
148 }
149
150 report_load(origin, NULL, operation: "old-api-denied");
151 return -EPERM;
152 }
153
154 load_root = file->f_path.mnt->mnt_sb;
155 load_root_writable = sb_is_writable(mnt_sb: load_root);
156
157 /* First loaded module/firmware defines the root for all others. */
158 spin_lock(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(lock: &pinned_root_spinlock);
169
170 if (first_root_pin) {
171 report_writable(mnt_sb: pinned_root, writable: load_root_writable);
172 set_sysctl(load_root_writable);
173 report_load(origin, file, operation: "pinned");
174 }
175
176 if (IS_ERR_OR_NULL(ptr: pinned_root) ||
177 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(bdev: load_root->s_bdev))) {
178 if (unlikely(!enforce)) {
179 report_load(origin, file, operation: "pinning-ignored");
180 return 0;
181 }
182
183 report_load(origin, file, operation: "denied");
184 return -EPERM;
185 }
186
187 return 0;
188}
189
190static 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
201static 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, id: (enum kernel_read_file_id) id);
209}
210
211static const struct lsm_id loadpin_lsmid = {
212 .name = "loadpin",
213 .id = LSM_ID_LOADPIN,
214};
215
216static 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
222static 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
258static 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(hooks: loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
268 lsmid: &loadpin_lsmid);
269
270 return 0;
271}
272
273#ifdef CONFIG_SECURITY_LOADPIN_VERITY
274
275enum loadpin_securityfs_interface_index {
276 LOADPIN_DM_VERITY,
277};
278
279static int read_trusted_verity_root_digests(unsigned int fd)
280{
281 void *data;
282 int rc;
283 char *p, *d;
284
285 if (deny_reading_verity_digests)
286 return -EPERM;
287
288 /* The list of trusted root digests can only be set up once */
289 if (!list_empty(head: &dm_verity_loadpin_trusted_root_digests))
290 return -EPERM;
291
292 CLASS(fd, f)(fd);
293 if (fd_empty(f))
294 return -EINVAL;
295
296 data = kzalloc(SZ_4K, GFP_KERNEL);
297 if (!data) {
298 rc = -ENOMEM;
299 goto err;
300 }
301
302 rc = kernel_read_file(fd_file(f), offset: 0, buf: (void **)&data, SZ_4K - 1, NULL, id: READING_POLICY);
303 if (rc < 0)
304 goto err;
305
306 p = data;
307 p[rc] = '\0';
308 p = strim(p);
309
310 p = strim(data);
311 while ((d = strsep(&p, "\n")) != NULL) {
312 int len;
313 struct dm_verity_loadpin_trusted_root_digest *trd;
314
315 if (d == data) {
316 /* first line, validate header */
317 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
318 rc = -EPROTO;
319 goto err;
320 }
321
322 continue;
323 }
324
325 len = strlen(d);
326
327 if (len % 2) {
328 rc = -EPROTO;
329 goto err;
330 }
331
332 len /= 2;
333
334 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
335 if (!trd) {
336 rc = -ENOMEM;
337 goto err;
338 }
339 trd->len = len;
340
341 if (hex2bin(dst: trd->data, src: d, count: len)) {
342 kfree(objp: trd);
343 rc = -EPROTO;
344 goto err;
345 }
346
347 list_add_tail(new: &trd->node, head: &dm_verity_loadpin_trusted_root_digests);
348 }
349
350 if (list_empty(head: &dm_verity_loadpin_trusted_root_digests)) {
351 rc = -EPROTO;
352 goto err;
353 }
354
355 kfree(objp: data);
356
357 return 0;
358
359err:
360 kfree(objp: data);
361
362 /* any failure in loading/parsing invalidates the entire list */
363 {
364 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
365
366 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
367 list_del(entry: &trd->node);
368 kfree(objp: trd);
369 }
370 }
371
372 /* disallow further attempts after reading a corrupt/invalid file */
373 deny_reading_verity_digests = true;
374
375 return rc;
376}
377
378/******************************** securityfs ********************************/
379
380static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
381{
382 void __user *uarg = (void __user *)arg;
383 unsigned int fd;
384
385 switch (cmd) {
386 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
387 if (copy_from_user(to: &fd, from: uarg, n: sizeof(fd)))
388 return -EFAULT;
389
390 return read_trusted_verity_root_digests(fd);
391
392 default:
393 return -EINVAL;
394 }
395}
396
397static const struct file_operations loadpin_dm_verity_ops = {
398 .unlocked_ioctl = dm_verity_ioctl,
399 .compat_ioctl = compat_ptr_ioctl,
400};
401
402/**
403 * init_loadpin_securityfs - create the securityfs directory for LoadPin
404 *
405 * We can not put this method normally under the loadpin_init() code path since
406 * the security subsystem gets initialized before the vfs caches.
407 *
408 * Returns 0 if the securityfs directory creation was successful.
409 */
410static int __init init_loadpin_securityfs(void)
411{
412 struct dentry *loadpin_dir, *dentry;
413
414 loadpin_dir = securityfs_create_dir(name: "loadpin", NULL);
415 if (IS_ERR(ptr: loadpin_dir)) {
416 pr_err("LoadPin: could not create securityfs dir: %ld\n",
417 PTR_ERR(loadpin_dir));
418 return PTR_ERR(ptr: loadpin_dir);
419 }
420
421 dentry = securityfs_create_file(name: "dm-verity", mode: 0600, parent: loadpin_dir,
422 data: (void *)LOADPIN_DM_VERITY, fops: &loadpin_dm_verity_ops);
423 if (IS_ERR(ptr: dentry)) {
424 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
425 PTR_ERR(dentry));
426 return PTR_ERR(ptr: dentry);
427 }
428
429 return 0;
430}
431
432#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
433
434DEFINE_LSM(loadpin) = {
435 .id = &loadpin_lsmid,
436 .init = loadpin_init,
437#ifdef CONFIG_SECURITY_LOADPIN_VERITY
438 .initcall_fs = init_loadpin_securityfs,
439#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
440};
441
442/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
443module_param(enforce, int, 0);
444MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
445module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
446MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
447

source code of linux/security/loadpin/loadpin.c