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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 <[email protected]>
8 */
9
10#define pr_fmt(fmt) "LoadPin: " fmt
11
12#include <linux/module.h>
13#include <linux/fs.h>
14#include <linux/hex.h>
15#include <linux/kernel_read_file.h>
16#include <linux/lsm_hooks.h>
17#include <linux/mount.h>
18#include <linux/blkdev.h>
19#include <linux/path.h>
20#include <linux/sched.h> /* current */
21#include <linux/string_helpers.h>
22#include <linux/dm-verity-loadpin.h>
23#include <uapi/linux/loadpin.h>
24#include <uapi/linux/lsm.h>
25
26#define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS"
27
28static void report_load(const char *origin, struct file *file, char *operation)
29{
30 char *cmdline, *pathname;
31
32 pathname = kstrdup_quotable_file(file, GFP_KERNEL);
33 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
34
35 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
36 origin, operation,
37 (pathname && pathname[0] != '<') ? "\"" : "",
38 pathname,
39 (pathname && pathname[0] != '<') ? "\"" : "",
40 task_pid_nr(current),
41 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
42
43 kfree(cmdline);
44 kfree(pathname);
45}
46
47static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
48static char *exclude_read_files[READING_MAX_ID];
49static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
50static struct super_block *pinned_root;
51static DEFINE_SPINLOCK(pinned_root_spinlock);
52#ifdef CONFIG_SECURITY_LOADPIN_VERITY
53static bool deny_reading_verity_digests;
54#endif
55
56// initialized to false
57static bool loadpin_root_writable;
58#ifdef CONFIG_SYSCTL
59
60static int proc_handler_loadpin(const struct ctl_table *table, int dir,
61 void *buffer, size_t *lenp, loff_t *ppos)
62{
63 if (!loadpin_root_writable && SYSCTL_USER_TO_KERN(dir))
64 return -EINVAL;
65 return proc_dointvec_minmax(table, dir, buffer, lenp, ppos);
66}
67
68static const struct ctl_table loadpin_sysctl_table[] = {
69 {
70 .procname = "enforce",
71 .data = &enforce,
72 .maxlen = sizeof(int),
73 .mode = 0644,
74 .proc_handler = proc_handler_loadpin,
75 .extra1 = SYSCTL_ZERO,
76 .extra2 = SYSCTL_ONE,
77 },
78};
79#endif
80
81static void report_writable(struct super_block *mnt_sb, bool writable)
82{
83 if (mnt_sb->s_bdev) {
84 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
85 MAJOR(mnt_sb->s_bdev->bd_dev),
86 MINOR(mnt_sb->s_bdev->bd_dev),
87 writable ? "writable" : "read-only");
88 } else
89 pr_info("mnt_sb lacks block device, treating as: writable\n");
90
91 if (!writable)
92 pr_info("load pinning engaged.\n");
93}
94
95/*
96 * This must be called after early kernel init, since then the rootdev
97 * is available.
98 */
99static bool sb_is_writable(struct super_block *mnt_sb)
100{
101 bool writable = true;
102
103 if (mnt_sb->s_bdev)
104 writable = !bdev_read_only(mnt_sb->s_bdev);
105
106 return writable;
107}
108
109static void loadpin_sb_free_security(struct super_block *mnt_sb)
110{
111 /*
112 * When unmounting the filesystem we were using for load
113 * pinning, we acknowledge the superblock release, but make sure
114 * no other modules or firmware can be loaded when we are in
115 * enforcing mode. Otherwise, allow the root to be reestablished.
116 */
117 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
118 if (enforce) {
119 pinned_root = ERR_PTR(-EIO);
120 pr_info("umount pinned fs: refusing further loads\n");
121 } else {
122 pinned_root = NULL;
123 }
124 }
125}
126
127static int loadpin_check(struct file *file, enum kernel_read_file_id id)
128{
129 struct super_block *load_root;
130 const char *origin = kernel_read_file_id_str(id);
131 bool first_root_pin = false;
132
133 /* If the file id is excluded, ignore the pinning. */
134 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
135 ignore_read_file_id[id]) {
136 report_load(origin, file, "pinning-excluded");
137 return 0;
138 }
139
140 /* This handles the older init_module API that has a NULL file. */
141 if (!file) {
142 if (!enforce) {
143 report_load(origin, NULL, "old-api-pinning-ignored");
144 return 0;
145 }
146
147 report_load(origin, NULL, "old-api-denied");
148 return -EPERM;
149 }
150
151 load_root = file->f_path.mnt->mnt_sb;
152
153 /* First loaded module/firmware defines the root for all others. */
154 spin_lock(&pinned_root_spinlock);
155 /*
156 * pinned_root is only NULL at startup or when the pinned root has
157 * been unmounted while we are not in enforcing mode. Otherwise, it
158 * is either a valid reference, or an ERR_PTR.
159 */
160 if (!pinned_root) {
161 pinned_root = load_root;
162 first_root_pin = true;
163 }
164 spin_unlock(&pinned_root_spinlock);
165
166 if (first_root_pin) {
167 loadpin_root_writable = sb_is_writable(pinned_root);
168 report_writable(pinned_root, loadpin_root_writable);
169 report_load(origin, file, "pinned");
170 }
171
172 if (IS_ERR_OR_NULL(pinned_root) ||
173 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
174 if (unlikely(!enforce)) {
175 report_load(origin, file, "pinning-ignored");
176 return 0;
177 }
178
179 report_load(origin, file, "denied");
180 return -EPERM;
181 }
182
183 return 0;
184}
185
186static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
187 bool contents)
188{
189 /*
190 * LoadPin only cares about the _origin_ of a file, not its
191 * contents, so we can ignore the "are full contents available"
192 * argument here.
193 */
194 return loadpin_check(file, id);
195}
196
197static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
198{
199 /*
200 * LoadPin only cares about the _origin_ of a file, not its
201 * contents, so a NULL file is passed, and we can ignore the
202 * state of "contents".
203 */
204 return loadpin_check(NULL, (enum kernel_read_file_id) id);
205}
206
207static const struct lsm_id loadpin_lsmid = {
208 .name = "loadpin",
209 .id = LSM_ID_LOADPIN,
210};
211
212static struct security_hook_list loadpin_hooks[] __ro_after_init = {
213 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
214 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
215 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
216};
217
218static void __init parse_exclude(void)
219{
220 int i, j;
221 char *cur;
222
223 /*
224 * Make sure all the arrays stay within expected sizes. This
225 * is slightly weird because kernel_read_file_str[] includes
226 * READING_MAX_ID, which isn't actually meaningful here.
227 */
228 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
229 ARRAY_SIZE(ignore_read_file_id));
230 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
231 ARRAY_SIZE(ignore_read_file_id));
232
233 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
234 cur = exclude_read_files[i];
235 if (!cur)
236 break;
237 if (*cur == '\0')
238 continue;
239
240 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
241 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
242 pr_info("excluding: %s\n",
243 kernel_read_file_str[j]);
244 ignore_read_file_id[j] = 1;
245 /*
246 * Can not break, because one read_file_str
247 * may map to more than on read_file_id.
248 */
249 }
250 }
251 }
252}
253
254static int __init loadpin_init(void)
255{
256 pr_info("ready to pin (currently %senforcing)\n",
257 enforce ? "" : "not ");
258 parse_exclude();
259#ifdef CONFIG_SYSCTL
260 if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
261 pr_notice("sysctl registration failed!\n");
262#endif
263 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
264 &loadpin_lsmid);
265
266 return 0;
267}
268
269#ifdef CONFIG_SECURITY_LOADPIN_VERITY
270
271enum loadpin_securityfs_interface_index {
272 LOADPIN_DM_VERITY,
273};
274
275static int read_trusted_verity_root_digests(unsigned int fd)
276{
277 void *data;
278 int rc;
279 char *p, *d;
280
281 if (deny_reading_verity_digests)
282 return -EPERM;
283
284 /* The list of trusted root digests can only be set up once */
285 if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
286 return -EPERM;
287
288 CLASS(fd, f)(fd);
289 if (fd_empty(f))
290 return -EINVAL;
291
292 data = kzalloc(SZ_4K, GFP_KERNEL);
293 if (!data) {
294 rc = -ENOMEM;
295 goto err;
296 }
297
298 rc = kernel_read_file(fd_file(f), 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
299 if (rc < 0)
300 goto err;
301
302 p = data;
303 p[rc] = '\0';
304 p = strim(p);
305
306 p = strim(data);
307 while ((d = strsep(&p, "\n")) != NULL) {
308 int len;
309 struct dm_verity_loadpin_trusted_root_digest *trd;
310
311 if (d == data) {
312 /* first line, validate header */
313 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
314 rc = -EPROTO;
315 goto err;
316 }
317
318 continue;
319 }
320
321 len = strlen(d);
322
323 if (len % 2) {
324 rc = -EPROTO;
325 goto err;
326 }
327
328 len /= 2;
329
330 trd = kzalloc_flex(*trd, data, len);
331 if (!trd) {
332 rc = -ENOMEM;
333 goto err;
334 }
335 trd->len = len;
336
337 if (hex2bin(trd->data, d, len)) {
338 kfree(trd);
339 rc = -EPROTO;
340 goto err;
341 }
342
343 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
344 }
345
346 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
347 rc = -EPROTO;
348 goto err;
349 }
350
351 kfree(data);
352
353 return 0;
354
355err:
356 kfree(data);
357
358 /* any failure in loading/parsing invalidates the entire list */
359 {
360 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
361
362 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
363 list_del(&trd->node);
364 kfree(trd);
365 }
366 }
367
368 /* disallow further attempts after reading a corrupt/invalid file */
369 deny_reading_verity_digests = true;
370
371 return rc;
372}
373
374/******************************** securityfs ********************************/
375
376static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
377{
378 void __user *uarg = (void __user *)arg;
379 unsigned int fd;
380
381 switch (cmd) {
382 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
383 if (copy_from_user(&fd, uarg, sizeof(fd)))
384 return -EFAULT;
385
386 return read_trusted_verity_root_digests(fd);
387
388 default:
389 return -EINVAL;
390 }
391}
392
393static const struct file_operations loadpin_dm_verity_ops = {
394 .unlocked_ioctl = dm_verity_ioctl,
395 .compat_ioctl = compat_ptr_ioctl,
396};
397
398/**
399 * init_loadpin_securityfs - create the securityfs directory for LoadPin
400 *
401 * We can not put this method normally under the loadpin_init() code path since
402 * the security subsystem gets initialized before the vfs caches.
403 *
404 * Returns 0 if the securityfs directory creation was successful.
405 */
406static int __init init_loadpin_securityfs(void)
407{
408 struct dentry *loadpin_dir, *dentry;
409
410 loadpin_dir = securityfs_create_dir("loadpin", NULL);
411 if (IS_ERR(loadpin_dir)) {
412 pr_err("LoadPin: could not create securityfs dir: %ld\n",
413 PTR_ERR(loadpin_dir));
414 return PTR_ERR(loadpin_dir);
415 }
416
417 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
418 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
419 if (IS_ERR(dentry)) {
420 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
421 PTR_ERR(dentry));
422 return PTR_ERR(dentry);
423 }
424
425 return 0;
426}
427
428#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
429
430DEFINE_LSM(loadpin) = {
431 .id = &loadpin_lsmid,
432 .init = loadpin_init,
433#ifdef CONFIG_SECURITY_LOADPIN_VERITY
434 .initcall_fs = init_loadpin_securityfs,
435#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
436};
437
438/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
439module_param(enforce, int, 0);
440MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
441module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
442MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");