summaryrefslogtreecommitdiffstats
path: root/security/loadpin/loadpin.c
blob: 8e93cda130f13c334f33add8ee7ae98e53534ae7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Module and Firmware Pinning Security Module
 *
 * Copyright 2011-2016 Google Inc.
 *
 * Author: Kees Cook <keescook@chromium.org>
 */

#define pr_fmt(fmt) "LoadPin: " fmt

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/kernel_read_file.h>
#include <linux/lsm_hooks.h>
#include <linux/mount.h>
#include <linux/blkdev.h>
#include <linux/path.h>
#include <linux/sched.h>	/* current */
#include <linux/string_helpers.h>
#include <linux/dm-verity-loadpin.h>
#include <uapi/linux/loadpin.h>
#include <uapi/linux/lsm.h>

#define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS"

static void report_load(const char *origin, struct file *file, char *operation)
{
	char *cmdline, *pathname;

	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);

	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
		  origin, operation,
		  (pathname && pathname[0] != '<') ? "\"" : "",
		  pathname,
		  (pathname && pathname[0] != '<') ? "\"" : "",
		  task_pid_nr(current),
		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");

	kfree(cmdline);
	kfree(pathname);
}

static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
static char *exclude_read_files[READING_MAX_ID];
static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
static struct super_block *pinned_root;
static DEFINE_SPINLOCK(pinned_root_spinlock);
#ifdef CONFIG_SECURITY_LOADPIN_VERITY
static bool deny_reading_verity_digests;
#endif

#ifdef CONFIG_SYSCTL
static struct ctl_table loadpin_sysctl_table[] = {
	{
		.procname       = "enforce",
		.data           = &enforce,
		.maxlen         = sizeof(int),
		.mode           = 0644,
		.proc_handler   = proc_dointvec_minmax,
		.extra1         = SYSCTL_ONE,
		.extra2         = SYSCTL_ONE,
	},
	{ }
};

static void set_sysctl(bool is_writable)
{
	/*
	 * If load pinning is not enforced via a read-only block
	 * device, allow sysctl to change modes for testing.
	 */
	if (is_writable)
		loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
	else
		loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
}
#else
static inline void set_sysctl(bool is_writable) { }
#endif

static void report_writable(struct super_block *mnt_sb, bool writable)
{
	if (mnt_sb->s_bdev) {
		pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
			MAJOR(mnt_sb->s_bdev->bd_dev),
			MINOR(mnt_sb->s_bdev->bd_dev),
			writable ? "writable" : "read-only");
	} else
		pr_info("mnt_sb lacks block device, treating as: writable\n");

	if (!writable)
		pr_info("load pinning engaged.\n");
}

/*
 * This must be called after early kernel init, since then the rootdev
 * is available.
 */
static bool sb_is_writable(struct super_block *mnt_sb)
{
	bool writable = true;

	if (mnt_sb->s_bdev)
		writable = !bdev_read_only(mnt_sb->s_bdev);

	return writable;
}

static void loadpin_sb_free_security(struct super_block *mnt_sb)
{
	/*
	 * When unmounting the filesystem we were using for load
	 * pinning, we acknowledge the superblock release, but make sure
	 * no other modules or firmware can be loaded when we are in
	 * enforcing mode. Otherwise, allow the root to be reestablished.
	 */
	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
		if (enforce) {
			pinned_root = ERR_PTR(-EIO);
			pr_info("umount pinned fs: refusing further loads\n");
		} else {
			pinned_root = NULL;
		}
	}
}

static int loadpin_check(struct file *file, enum kernel_read_file_id id)
{
	struct super_block *load_root;
	const char *origin = kernel_read_file_id_str(id);
	bool first_root_pin = false;
	bool load_root_writable;

	/* If the file id is excluded, ignore the pinning. */
	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
	    ignore_read_file_id[id]) {
		report_load(origin, file, "pinning-excluded");
		return 0;
	}

	/* This handles the older init_module API that has a NULL file. */
	if (!file) {
		if (!enforce) {
			report_load(origin, NULL, "old-api-pinning-ignored");
			return 0;
		}

		report_load(origin, NULL, "old-api-denied");
		return -EPERM;
	}

	load_root = file->f_path.mnt->mnt_sb;
	load_root_writable = sb_is_writable(load_root);

	/* First loaded module/firmware defines the root for all others. */
	spin_lock(&pinned_root_spinlock);
	/*
	 * pinned_root is only NULL at startup or when the pinned root has
	 * been unmounted while we are not in enforcing mode. Otherwise, it
	 * is either a valid reference, or an ERR_PTR.
	 */
	if (!pinned_root) {
		pinned_root = load_root;
		first_root_pin = true;
	}
	spin_unlock(&pinned_root_spinlock);

	if (first_root_pin) {
		report_writable(pinned_root, load_root_writable);
		set_sysctl(load_root_writable);
		report_load(origin, file, "pinned");
	}

	if (IS_ERR_OR_NULL(pinned_root) ||
	    ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
		if (unlikely(!enforce)) {
			report_load(origin, file, "pinning-ignored");
			return 0;
		}

		report_load(origin, file, "denied");
		return -EPERM;
	}

	return 0;
}

static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
			     bool contents)
{
	/*
	 * LoadPin only cares about the _origin_ of a file, not its
	 * contents, so we can ignore the "are full contents available"
	 * argument here.
	 */
	return loadpin_check(file, id);
}

static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
{
	/*
	 * LoadPin only cares about the _origin_ of a file, not its
	 * contents, so a NULL file is passed, and we can ignore the
	 * state of "contents".
	 */
	return loadpin_check(NULL, (enum kernel_read_file_id) id);
}

static const struct lsm_id loadpin_lsmid = {
	.name = "loadpin",
	.id = LSM_ID_LOADPIN,
};

static struct security_hook_list loadpin_hooks[] __ro_after_init = {
	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
};

static void __init parse_exclude(void)
{
	int i, j;
	char *cur;

	/*
	 * Make sure all the arrays stay within expected sizes. This
	 * is slightly weird because kernel_read_file_str[] includes
	 * READING_MAX_ID, which isn't actually meaningful here.
	 */
	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
		     ARRAY_SIZE(ignore_read_file_id));
	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
		     ARRAY_SIZE(ignore_read_file_id));

	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
		cur = exclude_read_files[i];
		if (!cur)
			break;
		if (*cur == '\0')
			continue;

		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
				pr_info("excluding: %s\n",
					kernel_read_file_str[j]);
				ignore_read_file_id[j] = 1;
				/*
				 * Can not break, because one read_file_str
				 * may map to more than on read_file_id.
				 */
			}
		}
	}
}

static int __init loadpin_init(void)
{
	pr_info("ready to pin (currently %senforcing)\n",
		enforce ? "" : "not ");
	parse_exclude();
#ifdef CONFIG_SYSCTL
	if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table))
		pr_notice("sysctl registration failed!\n");
#endif
	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks),
			   &loadpin_lsmid);

	return 0;
}

DEFINE_LSM(loadpin) = {
	.name = "loadpin",
	.init = loadpin_init,
};

#ifdef CONFIG_SECURITY_LOADPIN_VERITY

enum loadpin_securityfs_interface_index {
	LOADPIN_DM_VERITY,
};

static int read_trusted_verity_root_digests(unsigned int fd)
{
	struct fd f;
	void *data;
	int rc;
	char *p, *d;

	if (deny_reading_verity_digests)
		return -EPERM;

	/* The list of trusted root digests can only be set up once */
	if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
		return -EPERM;

	f = fdget(fd);
	if (!f.file)
		return -EINVAL;

	data = kzalloc(SZ_4K, GFP_KERNEL);
	if (!data) {
		rc = -ENOMEM;
		goto err;
	}

	rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
	if (rc < 0)
		goto err;

	p = data;
	p[rc] = '\0';
	p = strim(p);

	p = strim(data);
	while ((d = strsep(&p, "\n")) != NULL) {
		int len;
		struct dm_verity_loadpin_trusted_root_digest *trd;

		if (d == data) {
			/* first line, validate header */
			if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
				rc = -EPROTO;
				goto err;
			}

			continue;
		}

		len = strlen(d);

		if (len % 2) {
			rc = -EPROTO;
			goto err;
		}

		len /= 2;

		trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
		if (!trd) {
			rc = -ENOMEM;
			goto err;
		}
		trd->len = len;

		if (hex2bin(trd->data, d, len)) {
			kfree(trd);
			rc = -EPROTO;
			goto err;
		}

		list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
	}

	if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
		rc = -EPROTO;
		goto err;
	}

	kfree(data);
	fdput(f);

	return 0;

err:
	kfree(data);

	/* any failure in loading/parsing invalidates the entire list */
	{
		struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;

		list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
			list_del(&trd->node);
			kfree(trd);
		}
	}

	/* disallow further attempts after reading a corrupt/invalid file */
	deny_reading_verity_digests = true;

	fdput(f);

	return rc;
}

/******************************** securityfs ********************************/

static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
	void __user *uarg = (void __user *)arg;
	unsigned int fd;

	switch (cmd) {
	case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
		if (copy_from_user(&fd, uarg, sizeof(fd)))
			return -EFAULT;

		return read_trusted_verity_root_digests(fd);

	default:
		return -EINVAL;
	}
}

static const struct file_operations loadpin_dm_verity_ops = {
	.unlocked_ioctl = dm_verity_ioctl,
	.compat_ioctl = compat_ptr_ioctl,
};

/**
 * init_loadpin_securityfs - create the securityfs directory for LoadPin
 *
 * We can not put this method normally under the loadpin_init() code path since
 * the security subsystem gets initialized before the vfs caches.
 *
 * Returns 0 if the securityfs directory creation was successful.
 */
static int __init init_loadpin_securityfs(void)
{
	struct dentry *loadpin_dir, *dentry;

	loadpin_dir = securityfs_create_dir("loadpin", NULL);
	if (IS_ERR(loadpin_dir)) {
		pr_err("LoadPin: could not create securityfs dir: %ld\n",
		       PTR_ERR(loadpin_dir));
		return PTR_ERR(loadpin_dir);
	}

	dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
					(void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
	if (IS_ERR(dentry)) {
		pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
		       PTR_ERR(dentry));
		return PTR_ERR(dentry);
	}

	return 0;
}

fs_initcall(init_loadpin_securityfs);

#endif /* CONFIG_SECURITY_LOADPIN_VERITY */

/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
module_param(enforce, int, 0);
MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");