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(cmdline);
43	kfree(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(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(pinned_root) && mnt_sb == pinned_root) {
120		if (enforce) {
121			pinned_root = ERR_PTR(-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, "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, "old-api-pinning-ignored");
147			return 0;
148		}
149
150		report_load(origin, NULL, "old-api-denied");
151		return -EPERM;
152	}
153
154	load_root = file->f_path.mnt->mnt_sb;
155	load_root_writable = sb_is_writable(load_root);
156
157	/* First loaded module/firmware defines the root for all others. */
158	spin_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(&pinned_root_spinlock);
169
170	if (first_root_pin) {
171		report_writable(pinned_root, load_root_writable);
172		set_sysctl(load_root_writable);
173		report_load(origin, file, "pinned");
174	}
175
176	if (IS_ERR_OR_NULL(pinned_root) ||
177	    ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
178		if (unlikely(!enforce)) {
179			report_load(origin, file, "pinning-ignored");
180			return 0;
181		}
182
183		report_load(origin, file, "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, (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(loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
268			   &loadpin_lsmid);
269
270	return 0;
271}
272
273DEFINE_LSM(loadpin) = {
274	.name = "loadpin",
275	.init = loadpin_init,
276};
277
278#ifdef CONFIG_SECURITY_LOADPIN_VERITY
279
280enum loadpin_securityfs_interface_index {
281	LOADPIN_DM_VERITY,
282};
283
284static int read_trusted_verity_root_digests(unsigned int fd)
285{
286	struct fd f;
287	void *data;
288	int rc;
289	char *p, *d;
290
291	if (deny_reading_verity_digests)
292		return -EPERM;
293
294	/* The list of trusted root digests can only be set up once */
295	if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
296		return -EPERM;
297
298	f = fdget(fd);
299	if (!f.file)
300		return -EINVAL;
301
302	data = kzalloc(SZ_4K, GFP_KERNEL);
303	if (!data) {
304		rc = -ENOMEM;
305		goto err;
306	}
307
308	rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
309	if (rc < 0)
310		goto err;
311
312	p = data;
313	p[rc] = '\0';
314	p = strim(p);
315
316	p = strim(data);
317	while ((d = strsep(&p, "\n")) != NULL) {
318		int len;
319		struct dm_verity_loadpin_trusted_root_digest *trd;
320
321		if (d == data) {
322			/* first line, validate header */
323			if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
324				rc = -EPROTO;
325				goto err;
326			}
327
328			continue;
329		}
330
331		len = strlen(d);
332
333		if (len % 2) {
334			rc = -EPROTO;
335			goto err;
336		}
337
338		len /= 2;
339
340		trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
341		if (!trd) {
342			rc = -ENOMEM;
343			goto err;
344		}
345		trd->len = len;
346
347		if (hex2bin(trd->data, d, len)) {
348			kfree(trd);
349			rc = -EPROTO;
350			goto err;
351		}
352
353		list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
354	}
355
356	if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
357		rc = -EPROTO;
358		goto err;
359	}
360
361	kfree(data);
362	fdput(f);
363
364	return 0;
365
366err:
367	kfree(data);
368
369	/* any failure in loading/parsing invalidates the entire list */
370	{
371		struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
372
373		list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
374			list_del(&trd->node);
375			kfree(trd);
376		}
377	}
378
379	/* disallow further attempts after reading a corrupt/invalid file */
380	deny_reading_verity_digests = true;
381
382	fdput(f);
383
384	return rc;
385}
386
387/******************************** securityfs ********************************/
388
389static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
390{
391	void __user *uarg = (void __user *)arg;
392	unsigned int fd;
393
394	switch (cmd) {
395	case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
396		if (copy_from_user(&fd, uarg, sizeof(fd)))
397			return -EFAULT;
398
399		return read_trusted_verity_root_digests(fd);
400
401	default:
402		return -EINVAL;
403	}
404}
405
406static const struct file_operations loadpin_dm_verity_ops = {
407	.unlocked_ioctl = dm_verity_ioctl,
408	.compat_ioctl = compat_ptr_ioctl,
409};
410
411/**
412 * init_loadpin_securityfs - create the securityfs directory for LoadPin
413 *
414 * We can not put this method normally under the loadpin_init() code path since
415 * the security subsystem gets initialized before the vfs caches.
416 *
417 * Returns 0 if the securityfs directory creation was successful.
418 */
419static int __init init_loadpin_securityfs(void)
420{
421	struct dentry *loadpin_dir, *dentry;
422
423	loadpin_dir = securityfs_create_dir("loadpin", NULL);
424	if (IS_ERR(loadpin_dir)) {
425		pr_err("LoadPin: could not create securityfs dir: %ld\n",
426		       PTR_ERR(loadpin_dir));
427		return PTR_ERR(loadpin_dir);
428	}
429
430	dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
431					(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
432	if (IS_ERR(dentry)) {
433		pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
434		       PTR_ERR(dentry));
435		return PTR_ERR(dentry);
436	}
437
438	return 0;
439}
440
441fs_initcall(init_loadpin_securityfs);
442
443#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
444
445/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
446module_param(enforce, int, 0);
447MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
448module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
449MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
450