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