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
55static struct ctl_table loadpin_sysctl_table[] = {
56	{
57		.procname       = "enforce",
58		.data           = &enforce,
59		.maxlen         = sizeof(int),
60		.mode           = 0644,
61		.proc_handler   = proc_dointvec_minmax,
62		.extra1         = SYSCTL_ONE,
63		.extra2         = SYSCTL_ONE,
64	},
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 struct security_hook_list loadpin_hooks[] __ro_after_init = {
212	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
213	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
214	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
215};
216
217static void __init parse_exclude(void)
218{
219	int i, j;
220	char *cur;
221
222	/*
223	 * Make sure all the arrays stay within expected sizes. This
224	 * is slightly weird because kernel_read_file_str[] includes
225	 * READING_MAX_ID, which isn't actually meaningful here.
226	 */
227	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
228		     ARRAY_SIZE(ignore_read_file_id));
229	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
230		     ARRAY_SIZE(ignore_read_file_id));
231
232	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
233		cur = exclude_read_files[i];
234		if (!cur)
235			break;
236		if (*cur == '\0')
237			continue;
238
239		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
240			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
241				pr_info("excluding: %s\n",
242					kernel_read_file_str[j]);
243				ignore_read_file_id[j] = 1;
244				/*
245				 * Can not break, because one read_file_str
246				 * may map to more than on read_file_id.
247				 */
248			}
249		}
250	}
251}
252
253static int __init loadpin_init(void)
254{
255	pr_info("ready to pin (currently %senforcing)\n",
256		enforce ? "" : "not ");
257	parse_exclude();
258#ifdef CONFIG_SYSCTL
259	if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
260		pr_notice("sysctl registration failed!\n");
261#endif
262	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
263
264	return 0;
265}
266
267DEFINE_LSM(loadpin) = {
268	.name = "loadpin",
269	.init = loadpin_init,
270};
271
272#ifdef CONFIG_SECURITY_LOADPIN_VERITY
273
274enum loadpin_securityfs_interface_index {
275	LOADPIN_DM_VERITY,
276};
277
278static int read_trusted_verity_root_digests(unsigned int fd)
279{
280	struct fd f;
281	void *data;
282	int rc;
283	char *p, *d;
284
285	if (deny_reading_verity_digests)
286		return -EPERM;
287
288	/* The list of trusted root digests can only be set up once */
289	if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
290		return -EPERM;
291
292	f = fdget(fd);
293	if (!f.file)
294		return -EINVAL;
295
296	data = kzalloc(SZ_4K, GFP_KERNEL);
297	if (!data) {
298		rc = -ENOMEM;
299		goto err;
300	}
301
302	rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
303	if (rc < 0)
304		goto err;
305
306	p = data;
307	p[rc] = '\0';
308	p = strim(p);
309
310	p = strim(data);
311	while ((d = strsep(&p, "\n")) != NULL) {
312		int len;
313		struct dm_verity_loadpin_trusted_root_digest *trd;
314
315		if (d == data) {
316			/* first line, validate header */
317			if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
318				rc = -EPROTO;
319				goto err;
320			}
321
322			continue;
323		}
324
325		len = strlen(d);
326
327		if (len % 2) {
328			rc = -EPROTO;
329			goto err;
330		}
331
332		len /= 2;
333
334		trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
335		if (!trd) {
336			rc = -ENOMEM;
337			goto err;
338		}
339		trd->len = len;
340
341		if (hex2bin(trd->data, d, len)) {
342			kfree(trd);
343			rc = -EPROTO;
344			goto err;
345		}
346
347		list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
348	}
349
350	if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
351		rc = -EPROTO;
352		goto err;
353	}
354
355	kfree(data);
356	fdput(f);
357
358	return 0;
359
360err:
361	kfree(data);
362
363	/* any failure in loading/parsing invalidates the entire list */
364	{
365		struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
366
367		list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
368			list_del(&trd->node);
369			kfree(trd);
370		}
371	}
372
373	/* disallow further attempts after reading a corrupt/invalid file */
374	deny_reading_verity_digests = true;
375
376	fdput(f);
377
378	return rc;
379}
380
381/******************************** securityfs ********************************/
382
383static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
384{
385	void __user *uarg = (void __user *)arg;
386	unsigned int fd;
387
388	switch (cmd) {
389	case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
390		if (copy_from_user(&fd, uarg, sizeof(fd)))
391			return -EFAULT;
392
393		return read_trusted_verity_root_digests(fd);
394
395	default:
396		return -EINVAL;
397	}
398}
399
400static const struct file_operations loadpin_dm_verity_ops = {
401	.unlocked_ioctl = dm_verity_ioctl,
402	.compat_ioctl = compat_ptr_ioctl,
403};
404
405/**
406 * init_loadpin_securityfs - create the securityfs directory for LoadPin
407 *
408 * We can not put this method normally under the loadpin_init() code path since
409 * the security subsystem gets initialized before the vfs caches.
410 *
411 * Returns 0 if the securityfs directory creation was successful.
412 */
413static int __init init_loadpin_securityfs(void)
414{
415	struct dentry *loadpin_dir, *dentry;
416
417	loadpin_dir = securityfs_create_dir("loadpin", NULL);
418	if (IS_ERR(loadpin_dir)) {
419		pr_err("LoadPin: could not create securityfs dir: %ld\n",
420		       PTR_ERR(loadpin_dir));
421		return PTR_ERR(loadpin_dir);
422	}
423
424	dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
425					(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
426	if (IS_ERR(dentry)) {
427		pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
428		       PTR_ERR(dentry));
429		return PTR_ERR(dentry);
430	}
431
432	return 0;
433}
434
435fs_initcall(init_loadpin_securityfs);
436
437#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
438
439/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
440module_param(enforce, int, 0);
441MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
442module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
443MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
444