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_read_file(struct file *file, enum kernel_read_file_id id,
122			     bool contents)
123{
124	struct super_block *load_root;
125	const char *origin = kernel_read_file_id_str(id);
126
127	/*
128	 * If we will not know that we'll be seeing the full contents
129	 * then we cannot trust a load will be complete and unchanged
130	 * off disk. Treat all contents=false hooks as if there were
131	 * no associated file struct.
132	 */
133	if (!contents)
134		file = NULL;
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
156	/* First loaded module/firmware defines the root for all others. */
157	spin_lock(&pinned_root_spinlock);
158	/*
159	 * pinned_root is only NULL at startup. Otherwise, it is either
160	 * a valid reference, or an ERR_PTR.
161	 */
162	if (!pinned_root) {
163		pinned_root = load_root;
164		/*
165		 * Unlock now since it's only pinned_root we care about.
166		 * In the worst case, we will (correctly) report pinning
167		 * failures before we have announced that pinning is
168		 * enforcing. This would be purely cosmetic.
169		 */
170		spin_unlock(&pinned_root_spinlock);
171		check_pinning_enforcement(pinned_root);
172		report_load(origin, file, "pinned");
173	} else {
174		spin_unlock(&pinned_root_spinlock);
175	}
176
177	if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
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_load_data(enum kernel_load_data_id id, bool contents)
191{
192	return loadpin_read_file(NULL, (enum kernel_read_file_id) id, contents);
193}
194
195static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
196	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
197	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
198	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
199};
200
201static void __init parse_exclude(void)
202{
203	int i, j;
204	char *cur;
205
206	/*
207	 * Make sure all the arrays stay within expected sizes. This
208	 * is slightly weird because kernel_read_file_str[] includes
209	 * READING_MAX_ID, which isn't actually meaningful here.
210	 */
211	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
212		     ARRAY_SIZE(ignore_read_file_id));
213	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
214		     ARRAY_SIZE(ignore_read_file_id));
215
216	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
217		cur = exclude_read_files[i];
218		if (!cur)
219			break;
220		if (*cur == '\0')
221			continue;
222
223		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
224			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
225				pr_info("excluding: %s\n",
226					kernel_read_file_str[j]);
227				ignore_read_file_id[j] = 1;
228				/*
229				 * Can not break, because one read_file_str
230				 * may map to more than on read_file_id.
231				 */
232			}
233		}
234	}
235}
236
237static int __init loadpin_init(void)
238{
239	pr_info("ready to pin (currently %senforcing)\n",
240		enforce ? "" : "not ");
241	parse_exclude();
242	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
243	return 0;
244}
245
246DEFINE_LSM(loadpin) = {
247	.name = "loadpin",
248	.init = loadpin_init,
249};
250
251/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
252module_param(enforce, int, 0);
253MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
254module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
255MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");