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