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};
68
69static void set_sysctl(bool is_writable)
70{
71	/*
72	 * If load pinning is not enforced via a read-only block
73	 * device, allow sysctl to change modes for testing.
74	 */
75	if (is_writable)
76		loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
77	else
78		loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
79}
80#else
81static inline void set_sysctl(bool is_writable) { }
82#endif
83
84static void report_writable(struct super_block *mnt_sb, bool writable)
85{
86	if (mnt_sb->s_bdev) {
87		pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
88			MAJOR(mnt_sb->s_bdev->bd_dev),
89			MINOR(mnt_sb->s_bdev->bd_dev),
90			writable ? "writable" : "read-only");
91	} else
92		pr_info("mnt_sb lacks block device, treating as: writable\n");
93
94	if (!writable)
95		pr_info("load pinning engaged.\n");
96}
97
98/*
99 * This must be called after early kernel init, since then the rootdev
100 * is available.
101 */
102static bool sb_is_writable(struct super_block *mnt_sb)
103{
104	bool writable = true;
105
106	if (mnt_sb->s_bdev)
107		writable = !bdev_read_only(mnt_sb->s_bdev);
108
109	return writable;
110}
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 when we are in
118	 * enforcing mode. Otherwise, allow the root to be reestablished.
119	 */
120	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
121		if (enforce) {
122			pinned_root = ERR_PTR(-EIO);
123			pr_info("umount pinned fs: refusing further loads\n");
124		} else {
125			pinned_root = NULL;
126		}
127	}
128}
129
130static int loadpin_check(struct file *file, enum kernel_read_file_id id)
131{
132	struct super_block *load_root;
133	const char *origin = kernel_read_file_id_str(id);
134	bool first_root_pin = false;
135	bool load_root_writable;
136
137	/* If the file id is excluded, ignore the pinning. */
138	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
139	    ignore_read_file_id[id]) {
140		report_load(origin, file, "pinning-excluded");
141		return 0;
142	}
143
144	/* This handles the older init_module API that has a NULL file. */
145	if (!file) {
146		if (!enforce) {
147			report_load(origin, NULL, "old-api-pinning-ignored");
148			return 0;
149		}
150
151		report_load(origin, NULL, "old-api-denied");
152		return -EPERM;
153	}
154
155	load_root = file->f_path.mnt->mnt_sb;
156	load_root_writable = sb_is_writable(load_root);
157
158	/* First loaded module/firmware defines the root for all others. */
159	spin_lock(&pinned_root_spinlock);
160	/*
161	 * pinned_root is only NULL at startup or when the pinned root has
162	 * been unmounted while we are not in enforcing mode. Otherwise, it
163	 * is either a valid reference, or an ERR_PTR.
164	 */
165	if (!pinned_root) {
166		pinned_root = load_root;
167		first_root_pin = true;
168	}
169	spin_unlock(&pinned_root_spinlock);
170
171	if (first_root_pin) {
172		report_writable(pinned_root, load_root_writable);
173		set_sysctl(load_root_writable);
174		report_load(origin, file, "pinned");
175	}
176
177	if (IS_ERR_OR_NULL(pinned_root) ||
178	    ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
179		if (unlikely(!enforce)) {
180			report_load(origin, file, "pinning-ignored");
181			return 0;
182		}
183
184		report_load(origin, file, "denied");
185		return -EPERM;
186	}
187
188	return 0;
189}
190
191static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
192			     bool contents)
193{
194	/*
195	 * LoadPin only cares about the _origin_ of a file, not its
196	 * contents, so we can ignore the "are full contents available"
197	 * argument here.
198	 */
199	return loadpin_check(file, id);
200}
201
202static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
203{
204	/*
205	 * LoadPin only cares about the _origin_ of a file, not its
206	 * contents, so a NULL file is passed, and we can ignore the
207	 * state of "contents".
208	 */
209	return loadpin_check(NULL, (enum kernel_read_file_id) id);
210}
211
212static const struct lsm_id loadpin_lsmid = {
213	.name = "loadpin",
214	.id = LSM_ID_LOADPIN,
215};
216
217static struct security_hook_list loadpin_hooks[] __ro_after_init = {
218	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
219	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
220	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
221};
222
223static void __init parse_exclude(void)
224{
225	int i, j;
226	char *cur;
227
228	/*
229	 * Make sure all the arrays stay within expected sizes. This
230	 * is slightly weird because kernel_read_file_str[] includes
231	 * READING_MAX_ID, which isn't actually meaningful here.
232	 */
233	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
234		     ARRAY_SIZE(ignore_read_file_id));
235	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
236		     ARRAY_SIZE(ignore_read_file_id));
237
238	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
239		cur = exclude_read_files[i];
240		if (!cur)
241			break;
242		if (*cur == '\0')
243			continue;
244
245		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
246			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
247				pr_info("excluding: %s\n",
248					kernel_read_file_str[j]);
249				ignore_read_file_id[j] = 1;
250				/*
251				 * Can not break, because one read_file_str
252				 * may map to more than on read_file_id.
253				 */
254			}
255		}
256	}
257}
258
259static int __init loadpin_init(void)
260{
261	pr_info("ready to pin (currently %senforcing)\n",
262		enforce ? "" : "not ");
263	parse_exclude();
264#ifdef CONFIG_SYSCTL
265	if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
266		pr_notice("sysctl registration failed!\n");
267#endif
268	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
269			   &loadpin_lsmid);
270
271	return 0;
272}
273
274DEFINE_LSM(loadpin) = {
275	.name = "loadpin",
276	.init = loadpin_init,
277};
278
279#ifdef CONFIG_SECURITY_LOADPIN_VERITY
280
281enum loadpin_securityfs_interface_index {
282	LOADPIN_DM_VERITY,
283};
284
285static int read_trusted_verity_root_digests(unsigned int fd)
286{
287	struct fd f;
288	void *data;
289	int rc;
290	char *p, *d;
291
292	if (deny_reading_verity_digests)
293		return -EPERM;
294
295	/* The list of trusted root digests can only be set up once */
296	if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
297		return -EPERM;
298
299	f = fdget(fd);
300	if (!f.file)
301		return -EINVAL;
302
303	data = kzalloc(SZ_4K, GFP_KERNEL);
304	if (!data) {
305		rc = -ENOMEM;
306		goto err;
307	}
308
309	rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
310	if (rc < 0)
311		goto err;
312
313	p = data;
314	p[rc] = '\0';
315	p = strim(p);
316
317	p = strim(data);
318	while ((d = strsep(&p, "\n")) != NULL) {
319		int len;
320		struct dm_verity_loadpin_trusted_root_digest *trd;
321
322		if (d == data) {
323			/* first line, validate header */
324			if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
325				rc = -EPROTO;
326				goto err;
327			}
328
329			continue;
330		}
331
332		len = strlen(d);
333
334		if (len % 2) {
335			rc = -EPROTO;
336			goto err;
337		}
338
339		len /= 2;
340
341		trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
342		if (!trd) {
343			rc = -ENOMEM;
344			goto err;
345		}
346		trd->len = len;
347
348		if (hex2bin(trd->data, d, len)) {
349			kfree(trd);
350			rc = -EPROTO;
351			goto err;
352		}
353
354		list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
355	}
356
357	if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
358		rc = -EPROTO;
359		goto err;
360	}
361
362	kfree(data);
363	fdput(f);
364
365	return 0;
366
367err:
368	kfree(data);
369
370	/* any failure in loading/parsing invalidates the entire list */
371	{
372		struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
373
374		list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
375			list_del(&trd->node);
376			kfree(trd);
377		}
378	}
379
380	/* disallow further attempts after reading a corrupt/invalid file */
381	deny_reading_verity_digests = true;
382
383	fdput(f);
384
385	return rc;
386}
387
388/******************************** securityfs ********************************/
389
390static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
391{
392	void __user *uarg = (void __user *)arg;
393	unsigned int fd;
394
395	switch (cmd) {
396	case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
397		if (copy_from_user(&fd, uarg, sizeof(fd)))
398			return -EFAULT;
399
400		return read_trusted_verity_root_digests(fd);
401
402	default:
403		return -EINVAL;
404	}
405}
406
407static const struct file_operations loadpin_dm_verity_ops = {
408	.unlocked_ioctl = dm_verity_ioctl,
409	.compat_ioctl = compat_ptr_ioctl,
410};
411
412/**
413 * init_loadpin_securityfs - create the securityfs directory for LoadPin
414 *
415 * We can not put this method normally under the loadpin_init() code path since
416 * the security subsystem gets initialized before the vfs caches.
417 *
418 * Returns 0 if the securityfs directory creation was successful.
419 */
420static int __init init_loadpin_securityfs(void)
421{
422	struct dentry *loadpin_dir, *dentry;
423
424	loadpin_dir = securityfs_create_dir("loadpin", NULL);
425	if (IS_ERR(loadpin_dir)) {
426		pr_err("LoadPin: could not create securityfs dir: %ld\n",
427		       PTR_ERR(loadpin_dir));
428		return PTR_ERR(loadpin_dir);
429	}
430
431	dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
432					(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
433	if (IS_ERR(dentry)) {
434		pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
435		       PTR_ERR(dentry));
436		return PTR_ERR(dentry);
437	}
438
439	return 0;
440}
441
442fs_initcall(init_loadpin_securityfs);
443
444#endif /* CONFIG_SECURITY_LOADPIN_VERITY */
445
446/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
447module_param(enforce, int, 0);
448MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
449module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
450MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
451