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
report_load(const char * origin,struct file * file,char * operation)26 static 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
45 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
46 static char *exclude_read_files[READING_MAX_ID];
47 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
48 static struct super_block *pinned_root;
49 static DEFINE_SPINLOCK(pinned_root_spinlock);
50 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
51 static bool deny_reading_verity_digests;
52 #endif
53
54 #ifdef CONFIG_SYSCTL
55
56 static struct ctl_path loadpin_sysctl_path[] = {
57 { .procname = "kernel", },
58 { .procname = "loadpin", },
59 { }
60 };
61
62 static 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 */
check_pinning_enforcement(struct super_block * mnt_sb)79 static 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
check_pinning_enforcement(struct super_block * mnt_sb)106 static void check_pinning_enforcement(struct super_block *mnt_sb)
107 {
108 pr_info("load pinning engaged.\n");
109 }
110 #endif
111
loadpin_sb_free_security(struct super_block * mnt_sb)112 static 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
loadpin_read_file(struct file * file,enum kernel_read_file_id id,bool contents)125 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
126 bool contents)
127 {
128 struct super_block *load_root;
129 const char *origin = kernel_read_file_id_str(id);
130
131 /*
132 * If we will not know that we'll be seeing the full contents
133 * then we cannot trust a load will be complete and unchanged
134 * off disk. Treat all contents=false hooks as if there were
135 * no associated file struct.
136 */
137 if (!contents)
138 file = NULL;
139
140 /* If the file id is excluded, ignore the pinning. */
141 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
142 ignore_read_file_id[id]) {
143 report_load(origin, file, "pinning-excluded");
144 return 0;
145 }
146
147 /* This handles the older init_module API that has a NULL file. */
148 if (!file) {
149 if (!enforce) {
150 report_load(origin, NULL, "old-api-pinning-ignored");
151 return 0;
152 }
153
154 report_load(origin, NULL, "old-api-denied");
155 return -EPERM;
156 }
157
158 load_root = file->f_path.mnt->mnt_sb;
159
160 /* First loaded module/firmware defines the root for all others. */
161 spin_lock(&pinned_root_spinlock);
162 /*
163 * pinned_root is only NULL at startup. Otherwise, it is either
164 * a valid reference, or an ERR_PTR.
165 */
166 if (!pinned_root) {
167 pinned_root = load_root;
168 /*
169 * Unlock now since it's only pinned_root we care about.
170 * In the worst case, we will (correctly) report pinning
171 * failures before we have announced that pinning is
172 * enforcing. This would be purely cosmetic.
173 */
174 spin_unlock(&pinned_root_spinlock);
175 check_pinning_enforcement(pinned_root);
176 report_load(origin, file, "pinned");
177 } else {
178 spin_unlock(&pinned_root_spinlock);
179 }
180
181 if (IS_ERR_OR_NULL(pinned_root) ||
182 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
183 if (unlikely(!enforce)) {
184 report_load(origin, file, "pinning-ignored");
185 return 0;
186 }
187
188 report_load(origin, file, "denied");
189 return -EPERM;
190 }
191
192 return 0;
193 }
194
loadpin_load_data(enum kernel_load_data_id id,bool contents)195 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
196 {
197 return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
198 }
199
200 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
201 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
202 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
203 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
204 };
205
parse_exclude(void)206 static void __init parse_exclude(void)
207 {
208 int i, j;
209 char *cur;
210
211 /*
212 * Make sure all the arrays stay within expected sizes. This
213 * is slightly weird because kernel_read_file_str[] includes
214 * READING_MAX_ID, which isn't actually meaningful here.
215 */
216 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
217 ARRAY_SIZE(ignore_read_file_id));
218 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
219 ARRAY_SIZE(ignore_read_file_id));
220
221 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
222 cur = exclude_read_files[i];
223 if (!cur)
224 break;
225 if (*cur == '\0')
226 continue;
227
228 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
229 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
230 pr_info("excluding: %s\n",
231 kernel_read_file_str[j]);
232 ignore_read_file_id[j] = 1;
233 /*
234 * Can not break, because one read_file_str
235 * may map to more than on read_file_id.
236 */
237 }
238 }
239 }
240 }
241
loadpin_init(void)242 static int __init loadpin_init(void)
243 {
244 pr_info("ready to pin (currently %senforcing)\n",
245 enforce ? "" : "not ");
246 parse_exclude();
247 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
248
249 return 0;
250 }
251
252 DEFINE_LSM(loadpin) = {
253 .name = "loadpin",
254 .init = loadpin_init,
255 };
256
257 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
258
259 enum loadpin_securityfs_interface_index {
260 LOADPIN_DM_VERITY,
261 };
262
read_trusted_verity_root_digests(unsigned int fd)263 static int read_trusted_verity_root_digests(unsigned int fd)
264 {
265 struct fd f;
266 void *data;
267 int rc;
268 char *p, *d;
269
270 if (deny_reading_verity_digests)
271 return -EPERM;
272
273 /* The list of trusted root digests can only be set up once */
274 if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
275 return -EPERM;
276
277 f = fdget(fd);
278 if (!f.file)
279 return -EINVAL;
280
281 data = kzalloc(SZ_4K, GFP_KERNEL);
282 if (!data) {
283 rc = -ENOMEM;
284 goto err;
285 }
286
287 rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
288 if (rc < 0)
289 goto err;
290
291 p = data;
292 p[rc] = '\0';
293 p = strim(p);
294
295 p = strim(data);
296 while ((d = strsep(&p, "\n")) != NULL) {
297 int len;
298 struct dm_verity_loadpin_trusted_root_digest *trd;
299
300 if (d == data) {
301 /* first line, validate header */
302 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
303 rc = -EPROTO;
304 goto err;
305 }
306
307 continue;
308 }
309
310 len = strlen(d);
311
312 if (len % 2) {
313 rc = -EPROTO;
314 goto err;
315 }
316
317 len /= 2;
318
319 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
320 if (!trd) {
321 rc = -ENOMEM;
322 goto err;
323 }
324
325 if (hex2bin(trd->data, d, len)) {
326 kfree(trd);
327 rc = -EPROTO;
328 goto err;
329 }
330
331 trd->len = len;
332
333 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
334 }
335
336 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
337 rc = -EPROTO;
338 goto err;
339 }
340
341 kfree(data);
342 fdput(f);
343
344 return 0;
345
346 err:
347 kfree(data);
348
349 /* any failure in loading/parsing invalidates the entire list */
350 {
351 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
352
353 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
354 list_del(&trd->node);
355 kfree(trd);
356 }
357 }
358
359 /* disallow further attempts after reading a corrupt/invalid file */
360 deny_reading_verity_digests = true;
361
362 fdput(f);
363
364 return rc;
365 }
366
367 /******************************** securityfs ********************************/
368
dm_verity_ioctl(struct file * filp,unsigned int cmd,unsigned long arg)369 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
370 {
371 void __user *uarg = (void __user *)arg;
372 unsigned int fd;
373
374 switch (cmd) {
375 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
376 if (copy_from_user(&fd, uarg, sizeof(fd)))
377 return -EFAULT;
378
379 return read_trusted_verity_root_digests(fd);
380
381 default:
382 return -EINVAL;
383 }
384 }
385
386 static const struct file_operations loadpin_dm_verity_ops = {
387 .unlocked_ioctl = dm_verity_ioctl,
388 .compat_ioctl = compat_ptr_ioctl,
389 };
390
391 /**
392 * init_loadpin_securityfs - create the securityfs directory for LoadPin
393 *
394 * We can not put this method normally under the loadpin_init() code path since
395 * the security subsystem gets initialized before the vfs caches.
396 *
397 * Returns 0 if the securityfs directory creation was successful.
398 */
init_loadpin_securityfs(void)399 static int __init init_loadpin_securityfs(void)
400 {
401 struct dentry *loadpin_dir, *dentry;
402
403 loadpin_dir = securityfs_create_dir("loadpin", NULL);
404 if (IS_ERR(loadpin_dir)) {
405 pr_err("LoadPin: could not create securityfs dir: %ld\n",
406 PTR_ERR(loadpin_dir));
407 return PTR_ERR(loadpin_dir);
408 }
409
410 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
411 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
412 if (IS_ERR(dentry)) {
413 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
414 PTR_ERR(dentry));
415 return PTR_ERR(dentry);
416 }
417
418 return 0;
419 }
420
421 fs_initcall(init_loadpin_securityfs);
422
423 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */
424
425 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
426 module_param(enforce, int, 0);
427 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
428 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
429 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
430
