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/lsm_hooks.h>
 15#include <linux/mount.h>
 16#include <linux/blkdev.h>
 17#include <linux/path.h>
 18#include <linux/sched.h>	/* current */
 19#include <linux/string_helpers.h>
 20
 21static void report_load(const char *origin, struct file *file, char *operation)
 22{
 23	char *cmdline, *pathname;
 24
 25	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
 26	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
 27
 28	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
 29		  origin, operation,
 30		  (pathname && pathname[0] != '<') ? "\"" : "",
 31		  pathname,
 32		  (pathname && pathname[0] != '<') ? "\"" : "",
 33		  task_pid_nr(current),
 34		  cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
 35
 36	kfree(cmdline);
 37	kfree(pathname);
 38}
 39
 40static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
 41static char *exclude_read_files[READING_MAX_ID];
 42static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
 43static struct super_block *pinned_root;
 44static DEFINE_SPINLOCK(pinned_root_spinlock);
 45
 46#ifdef CONFIG_SYSCTL
 47
 48static struct ctl_path loadpin_sysctl_path[] = {
 49	{ .procname = "kernel", },
 50	{ .procname = "loadpin", },
 51	{ }
 52};
 53
 54static struct ctl_table loadpin_sysctl_table[] = {
 55	{
 56		.procname       = "enforce",
 57		.data           = &enforce,
 58		.maxlen         = sizeof(int),
 59		.mode           = 0644,
 60		.proc_handler   = proc_dointvec_minmax,
 61		.extra1         = SYSCTL_ZERO,
 62		.extra2         = SYSCTL_ONE,
 63	},
 64	{ }
 65};
 66
 67/*
 68 * This must be called after early kernel init, since then the rootdev
 69 * is available.
 70 */
 71static void check_pinning_enforcement(struct super_block *mnt_sb)
 72{
 73	bool ro = false;
 74
 75	/*
 76	 * If load pinning is not enforced via a read-only block
 77	 * device, allow sysctl to change modes for testing.
 78	 */
 79	if (mnt_sb->s_bdev) {
 80		char bdev[BDEVNAME_SIZE];
 81
 82		ro = bdev_read_only(mnt_sb->s_bdev);
 83		bdevname(mnt_sb->s_bdev, bdev);
 84		pr_info("%s (%u:%u): %s\n", bdev,
 85			MAJOR(mnt_sb->s_bdev->bd_dev),
 86			MINOR(mnt_sb->s_bdev->bd_dev),
 87			ro ? "read-only" : "writable");
 88	} else
 89		pr_info("mnt_sb lacks block device, treating as: writable\n");
 90
 91	if (!ro) {
 92		if (!register_sysctl_paths(loadpin_sysctl_path,
 93					   loadpin_sysctl_table))
 94			pr_notice("sysctl registration failed!\n");
 95		else
 96			pr_info("enforcement can be disabled.\n");
 97	} else
 98		pr_info("load pinning engaged.\n");
 99}
100#else
101static void check_pinning_enforcement(struct super_block *mnt_sb)
102{
103	pr_info("load pinning engaged.\n");
104}
105#endif
106
107static void loadpin_sb_free_security(struct super_block *mnt_sb)
108{
109	/*
110	 * When unmounting the filesystem we were using for load
111	 * pinning, we acknowledge the superblock release, but make sure
112	 * no other modules or firmware can be loaded.
113	 */
114	if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
115		pinned_root = ERR_PTR(-EIO);
116		pr_info("umount pinned fs: refusing further loads\n");
117	}
118}
119
120static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
121{
122	struct super_block *load_root;
123	const char *origin = kernel_read_file_id_str(id);
124
125	/* If the file id is excluded, ignore the pinning. */
126	if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
127	    ignore_read_file_id[id]) {
128		report_load(origin, file, "pinning-excluded");
129		return 0;
130	}
131
132	/* This handles the older init_module API that has a NULL file. */
133	if (!file) {
134		if (!enforce) {
135			report_load(origin, NULL, "old-api-pinning-ignored");
136			return 0;
137		}
138
139		report_load(origin, NULL, "old-api-denied");
140		return -EPERM;
141	}
142
143	load_root = file->f_path.mnt->mnt_sb;
144
145	/* First loaded module/firmware defines the root for all others. */
146	spin_lock(&pinned_root_spinlock);
147	/*
148	 * pinned_root is only NULL at startup. Otherwise, it is either
149	 * a valid reference, or an ERR_PTR.
150	 */
151	if (!pinned_root) {
152		pinned_root = load_root;
153		/*
154		 * Unlock now since it's only pinned_root we care about.
155		 * In the worst case, we will (correctly) report pinning
156		 * failures before we have announced that pinning is
157		 * enforcing. This would be purely cosmetic.
158		 */
159		spin_unlock(&pinned_root_spinlock);
160		check_pinning_enforcement(pinned_root);
161		report_load(origin, file, "pinned");
162	} else {
163		spin_unlock(&pinned_root_spinlock);
164	}
165
166	if (IS_ERR_OR_NULL(pinned_root) || load_root != pinned_root) {
167		if (unlikely(!enforce)) {
168			report_load(origin, file, "pinning-ignored");
169			return 0;
170		}
171
172		report_load(origin, file, "denied");
173		return -EPERM;
174	}
175
176	return 0;
177}
178
179static int loadpin_load_data(enum kernel_load_data_id id)
180{
181	return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
182}
183
184static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
185	LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
186	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
187	LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
188};
189
190static void __init parse_exclude(void)
191{
192	int i, j;
193	char *cur;
194
195	/*
196	 * Make sure all the arrays stay within expected sizes. This
197	 * is slightly weird because kernel_read_file_str[] includes
198	 * READING_MAX_ID, which isn't actually meaningful here.
199	 */
200	BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
201		     ARRAY_SIZE(ignore_read_file_id));
202	BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
203		     ARRAY_SIZE(ignore_read_file_id));
204
205	for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
206		cur = exclude_read_files[i];
207		if (!cur)
208			break;
209		if (*cur == '\0')
210			continue;
211
212		for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
213			if (strcmp(cur, kernel_read_file_str[j]) == 0) {
214				pr_info("excluding: %s\n",
215					kernel_read_file_str[j]);
216				ignore_read_file_id[j] = 1;
217				/*
218				 * Can not break, because one read_file_str
219				 * may map to more than on read_file_id.
220				 */
221			}
222		}
223	}
224}
225
226static int __init loadpin_init(void)
227{
228	pr_info("ready to pin (currently %senforcing)\n",
229		enforce ? "" : "not ");
230	parse_exclude();
231	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
232	return 0;
233}
234
235DEFINE_LSM(loadpin) = {
236	.name = "loadpin",
237	.init = loadpin_init,
238};
239
240/* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
241module_param(enforce, int, 0);
242MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
243module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
244MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");