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};
68
69static void set_sysctl(bool is_writable)
70{
71 /*
72 * If load pinning is not enforced via a read-only block
73 * device, allow sysctl to change modes for testing.
74 */
75 if (is_writable)
76 loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
77 else
78 loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
79}
80#else
81static inline void set_sysctl(bool is_writable) { }
82#endif
83
84static void report_writable(struct super_block *mnt_sb, bool writable)
85{
86 if (mnt_sb->s_bdev) {
87 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
88 MAJOR(mnt_sb->s_bdev->bd_dev),
89 MINOR(mnt_sb->s_bdev->bd_dev),
90 writable ? "writable" : "read-only");
91 } else
92 pr_info("mnt_sb lacks block device, treating as: writable\n");
93
94 if (!writable)
95 pr_info("load pinning engaged.\n");
96}
97
98/*
99 * This must be called after early kernel init, since then the rootdev
100 * is available.
101 */
102static bool sb_is_writable(struct super_block *mnt_sb)
103{
104 bool writable = true;
105
106 if (mnt_sb->s_bdev)
107 writable = !bdev_read_only(bdev: mnt_sb->s_bdev);
108
109 return writable;
110}
111
112static void loadpin_sb_free_security(struct super_block *mnt_sb)
113{
114 /*
115 * When unmounting the filesystem we were using for load
116 * pinning, we acknowledge the superblock release, but make sure
117 * no other modules or firmware can be loaded when we are in
118 * enforcing mode. Otherwise, allow the root to be reestablished.
119 */
120 if (!IS_ERR_OR_NULL(ptr: pinned_root) && mnt_sb == pinned_root) {
121 if (enforce) {
122 pinned_root = ERR_PTR(error: -EIO);
123 pr_info("umount pinned fs: refusing further loads\n");
124 } else {
125 pinned_root = NULL;
126 }
127 }
128}
129
130static int loadpin_check(struct file *file, enum kernel_read_file_id id)
131{
132 struct super_block *load_root;
133 const char *origin = kernel_read_file_id_str(id);
134 bool first_root_pin = false;
135 bool load_root_writable;
136
137 /* If the file id is excluded, ignore the pinning. */
138 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
139 ignore_read_file_id[id]) {
140 report_load(origin, file, operation: "pinning-excluded");
141 return 0;
142 }
143
144 /* This handles the older init_module API that has a NULL file. */
145 if (!file) {
146 if (!enforce) {
147 report_load(origin, NULL, operation: "old-api-pinning-ignored");
148 return 0;
149 }
150
151 report_load(origin, NULL, operation: "old-api-denied");
152 return -EPERM;
153 }
154
155 load_root = file->f_path.mnt->mnt_sb;
156 load_root_writable = sb_is_writable(mnt_sb: load_root);
157
158 /* First loaded module/firmware defines the root for all others. */
159 spin_lock(lock: &pinned_root_spinlock);
160 /*
161 * pinned_root is only NULL at startup or when the pinned root has
162 * been unmounted while we are not in enforcing mode. Otherwise, it
163 * is either a valid reference, or an ERR_PTR.
164 */
165 if (!pinned_root) {
166 pinned_root = load_root;
167 first_root_pin = true;
168 }
169 spin_unlock(lock: &pinned_root_spinlock);
170
171 if (first_root_pin) {
172 report_writable(mnt_sb: pinned_root, writable: load_root_writable);
173 set_sysctl(load_root_writable);
174 report_load(origin, file, operation: "pinned");
175 }
176
177 if (IS_ERR_OR_NULL(ptr: pinned_root) ||
178 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(bdev: load_root->s_bdev))) {
179 if (unlikely(!enforce)) {
180 report_load(origin, file, operation: "pinning-ignored");
181 return 0;
182 }
183
184 report_load(origin, file, operation: "denied");
185 return -EPERM;
186 }
187
188 return 0;
189}
190
191static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
192 bool contents)
193{
194 /*
195 * LoadPin only cares about the _origin_ of a file, not its
196 * contents, so we can ignore the "are full contents available"
197 * argument here.
198 */
199 return loadpin_check(file, id);
200}
201
202static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
203{
204 /*
205 * LoadPin only cares about the _origin_ of a file, not its
206 * contents, so a NULL file is passed, and we can ignore the
207 * state of "contents".
208 */
209 return loadpin_check(NULL, id: (enum kernel_read_file_id) id);
210}
211
212static const struct lsm_id loadpin_lsmid = {
213 .name = "loadpin",
214 .id = LSM_ID_LOADPIN,
215};
216
217static struct security_hook_list loadpin_hooks[] __ro_after_init = {
218 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
219 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
220 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
221};
222
223static void __init parse_exclude(void)
224{
225 int i, j;
226 char *cur;
227
228 /*
229 * Make sure all the arrays stay within expected sizes. This
230 * is slightly weird because kernel_read_file_str[] includes
231 * READING_MAX_ID, which isn't actually meaningful here.
232 */
233 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
234 ARRAY_SIZE(ignore_read_file_id));
235 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
236 ARRAY_SIZE(ignore_read_file_id));
237
238 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
239 cur = exclude_read_files[i];
240 if (!cur)
241 break;
242 if (*cur == '\0')
243 continue;
244
245 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
246 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
247 pr_info("excluding: %s\n",
248 kernel_read_file_str[j]);
249 ignore_read_file_id[j] = 1;
250 /*
251 * Can not break, because one read_file_str
252 * may map to more than on read_file_id.
253 */
254 }
255 }
256 }
257}
258
259static int __init loadpin_init(void)
260{
261 pr_info("ready to pin (currently %senforcing)\n",
262 enforce ? "" : "not ");
263 parse_exclude();
264#ifdef CONFIG_SYSCTL
265 if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
266 pr_notice("sysctl registration failed!\n");
267#endif
268 security_add_hooks(hooks: loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
269 lsmid: &loadpin_lsmid);
270
271 return 0;
272}
273
274DEFINE_LSM(loadpin) = {
275 .name = "loadpin",
276 .init = loadpin_init,
277};
278
279#ifdef CONFIG_SECURITY_LOADPIN_VERITY
280
281enum loadpin_securityfs_interface_index {
282 LOADPIN_DM_VERITY,
283};
284
285static int read_trusted_verity_root_digests(unsigned int fd)
286{
287 struct fd f;
288 void *data;
289 int rc;
290 char *p, *d;
291
292 if (deny_reading_verity_digests)
293 return -EPERM;
294
295 /* The list of trusted root digests can only be set up once */
296 if (!list_empty(head: &dm_verity_loadpin_trusted_root_digests))
297 return -EPERM;
298
299 f = fdget(fd);
300 if (!f.file)
301 return -EINVAL;
302
303 data = kzalloc(SZ_4K, GFP_KERNEL);
304 if (!data) {
305 rc = -ENOMEM;
306 goto err;
307 }
308
309 rc = kernel_read_file(file: f.file, offset: 0, buf: (void **)&data, SZ_4K - 1, NULL, id: READING_POLICY);
310 if (rc < 0)
311 goto err;
312
313 p = data;
314 p[rc] = '\0';
315 p = strim(p);
316
317 p = strim(data);
318 while ((d = strsep(&p, "\n")) != NULL) {
319 int len;
320 struct dm_verity_loadpin_trusted_root_digest *trd;
321
322 if (d == data) {
323 /* first line, validate header */
324 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
325 rc = -EPROTO;
326 goto err;
327 }
328
329 continue;
330 }
331
332 len = strlen(d);
333
334 if (len % 2) {
335 rc = -EPROTO;
336 goto err;
337 }
338
339 len /= 2;
340
341 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
342 if (!trd) {
343 rc = -ENOMEM;
344 goto err;
345 }
346 trd->len = len;
347
348 if (hex2bin(dst: trd->data, src: d, count: len)) {
349 kfree(objp: trd);
350 rc = -EPROTO;
351 goto err;
352 }
353
354 list_add_tail(new: &trd->node, head: &dm_verity_loadpin_trusted_root_digests);
355 }
356
357 if (list_empty(head: &dm_verity_loadpin_trusted_root_digests)) {
358 rc = -EPROTO;
359 goto err;
360 }
361
362 kfree(objp: data);
363 fdput(fd: f);
364
365 return 0;
366
367err:
368 kfree(objp: data);
369
370 /* any failure in loading/parsing invalidates the entire list */
371 {
372 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
373
374 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
375 list_del(entry: &trd->node);
376 kfree(objp: trd);
377 }
378 }
379
380 /* disallow further attempts after reading a corrupt/invalid file */
381 deny_reading_verity_digests = true;
382
383 fdput(fd: f);
384
385 return rc;
386}
387
388/******************************** securityfs ********************************/
389
390static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
391{
392 void __user *uarg = (void __user *)arg;
393 unsigned int fd;
394
395 switch (cmd) {
396 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
397 if (copy_from_user(to: &fd, from: uarg, n: sizeof(fd)))
398 return -EFAULT;
399
400 return read_trusted_verity_root_digests(fd);
401
402 default:
403 return -EINVAL;
404 }
405}
406
407static const struct file_operations loadpin_dm_verity_ops = {
408 .unlocked_ioctl = dm_verity_ioctl,
409 .compat_ioctl = compat_ptr_ioctl,
410};
411
412/**
413 * init_loadpin_securityfs - create the securityfs directory for LoadPin
414 *
415 * We can not put this method normally under the loadpin_init() code path since
416 * the security subsystem gets initialized before the vfs caches.
417 *
418 * Returns 0 if the securityfs directory creation was successful.
419 */
420static int __init init_loadpin_securityfs(void)
421{
422 struct dentry *loadpin_dir, *dentry;
423
424 loadpin_dir = securityfs_create_dir(name: "loadpin", NULL);
425 if (IS_ERR(ptr: loadpin_dir)) {
426 pr_err("LoadPin: could not create securityfs dir: %ld\n",
427 PTR_ERR(loadpin_dir));
428 return PTR_ERR(ptr: loadpin_dir);
429 }
430
431 dentry = securityfs_create_file(name: "dm-verity", mode: 0600, parent: loadpin_dir,
432 data: (void *)LOADPIN_DM_VERITY, fops: &loadpin_dm_verity_ops);
433 if (IS_ERR(ptr: dentry)) {
434 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
435 PTR_ERR(dentry));
436 return PTR_ERR(ptr: dentry);
437 }
438
439 return 0;
440}
441
442fs_initcall(init_loadpin_securityfs);
443
444#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
445
446/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
447module_param(enforce, int, 0);
448MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
449module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
450MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
451

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