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
22static void report_load(const char *origin, struct file *file, char *operation)
23{
24	char *cmdline, *pathname;
25
26	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
27	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
28
29	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
30		  origin, operation,
31		  (pathname && pathname[0] != '<') ? "\"" : "",
32		  pathname,
33		  (pathname && pathname[0] != '<') ? "\"" : "",
34		  task_pid_nr(current),
35		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
36
37	kfree(cmdline);
38	kfree(pathname);
39}
40
41static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
42static char *exclude_read_files[READING_MAX_ID];
43static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
44static struct super_block *pinned_root;
45static DEFINE_SPINLOCK(pinned_root_spinlock);
46
47#ifdef CONFIG_SYSCTL
48
49static struct ctl_path loadpin_sysctl_path[] = {
50	{ .procname = "kernel", },
51	{ .procname = "loadpin", },
52	{ }
53};
54
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_ZERO,
63		.extra2         = SYSCTL_ONE,
64	},
65	{ }
66};
67
68/*
69 * This must be called after early kernel init, since then the rootdev
70 * is available.
71 */
72static void check_pinning_enforcement(struct super_block *mnt_sb)
73{
74	bool ro = false;
75
76	/*
77	 * If load pinning is not enforced via a read-only block
78	 * device, allow sysctl to change modes for testing.
79	 */
80	if (mnt_sb->s_bdev) {
81		char bdev[BDEVNAME_SIZE];
82
83		ro = bdev_read_only(mnt_sb->s_bdev);
84		bdevname(mnt_sb->s_bdev, bdev);
85		pr_info("%s (%u:%u): %s\n", bdev,
86			MAJOR(mnt_sb->s_bdev->bd_dev),
87			MINOR(mnt_sb->s_bdev->bd_dev),
88			ro ? "read-only" : "writable");
89	} else
90		pr_info("mnt_sb lacks block device, treating as: writable\n");
91
92	if (!ro) {
93		if (!register_sysctl_paths(loadpin_sysctl_path,
94					   loadpin_sysctl_table))
95			pr_notice("sysctl registration failed!\n");
96		else
97			pr_info("enforcement can be disabled.\n");
98	} else
99		pr_info("load pinning engaged.\n");
100}
101#else
102static void check_pinning_enforcement(struct super_block *mnt_sb)
103{
104	pr_info("load pinning engaged.\n");
105}
106#endif
107
108static void loadpin_sb_free_security(struct super_block *mnt_sb)
109{
110	/*
111	 * When unmounting the filesystem we were using for load
112	 * pinning, we acknowledge the superblock release, but make sure
113	 * no other modules or firmware can be loaded.
114	 */
115	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
116		pinned_root = ERR_PTR(-EIO);
117		pr_info("umount pinned fs: refusing further loads\n");
118	}
119}
120
121static int loadpin_check(struct file *file, enum kernel_read_file_id id)
122{
123	struct super_block *load_root;
124	const char *origin = kernel_read_file_id_str(id);
125
126	/* If the file id is excluded, ignore the pinning. */
127	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
128	    ignore_read_file_id[id]) {
129		report_load(origin, file, "pinning-excluded");
130		return 0;
131	}
132
133	/* This handles the older init_module API that has a NULL file. */
134	if (!file) {
135		if (!enforce) {
136			report_load(origin, NULL, "old-api-pinning-ignored");
137			return 0;
138		}
139
140		report_load(origin, NULL, "old-api-denied");
141		return -EPERM;
142	}
143
144	load_root = file->f_path.mnt->mnt_sb;
145
146	/* First loaded module/firmware defines the root for all others. */
147	spin_lock(&pinned_root_spinlock);
148	/*
149	 * pinned_root is only NULL at startup. Otherwise, it is either
150	 * a valid reference, or an ERR_PTR.
151	 */
152	if (!pinned_root) {
153		pinned_root = load_root;
154		/*
155		 * Unlock now since it's only pinned_root we care about.
156		 * In the worst case, we will (correctly) report pinning
157		 * failures before we have announced that pinning is
158		 * enforcing. This would be purely cosmetic.
159		 */
160		spin_unlock(&pinned_root_spinlock);
161		check_pinning_enforcement(pinned_root);
162		report_load(origin, file, "pinned");
163	} else {
164		spin_unlock(&pinned_root_spinlock);
165	}
166
167	if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
168		if (unlikely(!enforce)) {
169			report_load(origin, file, "pinning-ignored");
170			return 0;
171		}
172
173		report_load(origin, file, "denied");
174		return -EPERM;
175	}
176
177	return 0;
178}
179
180static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
181			     bool contents)
182{
183	/*
184	 * LoadPin only cares about the _origin_ of a file, not its
185	 * contents, so we can ignore the "are full contents available"
186	 * argument here.
187	 */
188	return loadpin_check(file, id);
189}
190
191static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
192{
193	/*
194	 * LoadPin only cares about the _origin_ of a file, not its
195	 * contents, so a NULL file is passed, and we can ignore the
196	 * state of "contents".
197	 */
198	return loadpin_check(NULL, (enum kernel_read_file_id) id);
199}
200
201static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
202	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
203	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
204	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
205};
206
207static void __init parse_exclude(void)
208{
209	int i, j;
210	char *cur;
211
212	/*
213	 * Make sure all the arrays stay within expected sizes. This
214	 * is slightly weird because kernel_read_file_str[] includes
215	 * READING_MAX_ID, which isn't actually meaningful here.
216	 */
217	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
218		     ARRAY_SIZE(ignore_read_file_id));
219	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
220		     ARRAY_SIZE(ignore_read_file_id));
221
222	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
223		cur = exclude_read_files[i];
224		if (!cur)
225			break;
226		if (*cur == '\0')
227			continue;
228
229		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
230			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
231				pr_info("excluding: %s\n",
232					kernel_read_file_str[j]);
233				ignore_read_file_id[j] = 1;
234				/*
235				 * Can not break, because one read_file_str
236				 * may map to more than on read_file_id.
237				 */
238			}
239		}
240	}
241}
242
243static int __init loadpin_init(void)
244{
245	pr_info("ready to pin (currently %senforcing)\n",
246		enforce ? "" : "not ");
247	parse_exclude();
248	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
249	return 0;
250}
251
252DEFINE_LSM(loadpin) = {
253	.name = "loadpin",
254	.init = loadpin_init,
255};
256
257/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
258module_param(enforce, int, 0);
259MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
260module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
261MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");
262