1 // SPDX-License-Identifier: GPL-2.0-only
3 * Module and Firmware Pinning Security Module
5 * Copyright 2011-2016 Google Inc.
7 * Author: Kees Cook <keescook@chromium.org>
10 #define pr_fmt(fmt) "LoadPin: " fmt
12 #include <linux/module.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 #include <linux/dm-verity-loadpin.h>
22 #include <uapi/linux/loadpin.h>
24 #define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS"
26 static void report_load(const char *origin, struct file *file, char *operation)
28 char *cmdline, *pathname;
30 pathname = kstrdup_quotable_file(file, GFP_KERNEL);
31 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
33 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
35 (pathname && pathname[0] != '<') ? "\"" : "",
37 (pathname && pathname[0] != '<') ? "\"" : "",
39 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : "");
45 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE);
46 static char *exclude_read_files[READING_MAX_ID];
47 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init;
48 static struct super_block *pinned_root;
49 static DEFINE_SPINLOCK(pinned_root_spinlock);
50 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
51 static bool deny_reading_verity_digests;
55 static struct ctl_path loadpin_sysctl_path[] = {
56 { .procname = "kernel", },
57 { .procname = "loadpin", },
61 static struct ctl_table loadpin_sysctl_table[] = {
63 .procname = "enforce",
65 .maxlen = sizeof(int),
67 .proc_handler = proc_dointvec_minmax,
74 static void set_sysctl(bool is_writable)
77 * If load pinning is not enforced via a read-only block
78 * device, allow sysctl to change modes for testing.
81 loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO;
83 loadpin_sysctl_table[0].extra1 = SYSCTL_ONE;
86 static inline void set_sysctl(bool is_writable) { }
89 static void report_writable(struct super_block *mnt_sb, bool writable)
92 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev,
93 MAJOR(mnt_sb->s_bdev->bd_dev),
94 MINOR(mnt_sb->s_bdev->bd_dev),
95 writable ? "writable" : "read-only");
97 pr_info("mnt_sb lacks block device, treating as: writable\n");
100 pr_info("load pinning engaged.\n");
104 * This must be called after early kernel init, since then the rootdev
107 static bool sb_is_writable(struct super_block *mnt_sb)
109 bool writable = true;
112 writable = !bdev_read_only(mnt_sb->s_bdev);
117 static void loadpin_sb_free_security(struct super_block *mnt_sb)
120 * When unmounting the filesystem we were using for load
121 * pinning, we acknowledge the superblock release, but make sure
122 * no other modules or firmware can be loaded when we are in
123 * enforcing mode. Otherwise, allow the root to be reestablished.
125 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) {
127 pinned_root = ERR_PTR(-EIO);
128 pr_info("umount pinned fs: refusing further loads\n");
135 static int loadpin_check(struct file *file, enum kernel_read_file_id id)
137 struct super_block *load_root;
138 const char *origin = kernel_read_file_id_str(id);
139 bool first_root_pin = false;
140 bool load_root_writable;
142 /* If the file id is excluded, ignore the pinning. */
143 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) &&
144 ignore_read_file_id[id]) {
145 report_load(origin, file, "pinning-excluded");
149 /* This handles the older init_module API that has a NULL file. */
152 report_load(origin, NULL, "old-api-pinning-ignored");
156 report_load(origin, NULL, "old-api-denied");
160 load_root = file->f_path.mnt->mnt_sb;
161 load_root_writable = sb_is_writable(load_root);
163 /* First loaded module/firmware defines the root for all others. */
164 spin_lock(&pinned_root_spinlock);
166 * pinned_root is only NULL at startup or when the pinned root has
167 * been unmounted while we are not in enforcing mode. Otherwise, it
168 * is either a valid reference, or an ERR_PTR.
171 pinned_root = load_root;
172 first_root_pin = true;
174 spin_unlock(&pinned_root_spinlock);
176 if (first_root_pin) {
177 report_writable(pinned_root, load_root_writable);
178 set_sysctl(load_root_writable);
179 report_load(origin, file, "pinned");
182 if (IS_ERR_OR_NULL(pinned_root) ||
183 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) {
184 if (unlikely(!enforce)) {
185 report_load(origin, file, "pinning-ignored");
189 report_load(origin, file, "denied");
196 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id,
200 * LoadPin only cares about the _origin_ of a file, not its
201 * contents, so we can ignore the "are full contents available"
204 return loadpin_check(file, id);
207 static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
210 * LoadPin only cares about the _origin_ of a file, not its
211 * contents, so a NULL file is passed, and we can ignore the
212 * state of "contents".
214 return loadpin_check(NULL, (enum kernel_read_file_id) id);
217 static struct security_hook_list loadpin_hooks[] __lsm_ro_after_init = {
218 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security),
219 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
220 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data),
223 static void __init parse_exclude(void)
229 * Make sure all the arrays stay within expected sizes. This
230 * is slightly weird because kernel_read_file_str[] includes
231 * READING_MAX_ID, which isn't actually meaningful here.
233 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) !=
234 ARRAY_SIZE(ignore_read_file_id));
235 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) <
236 ARRAY_SIZE(ignore_read_file_id));
238 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) {
239 cur = exclude_read_files[i];
245 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) {
246 if (strcmp(cur, kernel_read_file_str[j]) == 0) {
247 pr_info("excluding: %s\n",
248 kernel_read_file_str[j]);
249 ignore_read_file_id[j] = 1;
251 * Can not break, because one read_file_str
252 * may map to more than on read_file_id.
259 static int __init loadpin_init(void)
261 pr_info("ready to pin (currently %senforcing)\n",
262 enforce ? "" : "not ");
265 if (!register_sysctl_paths(loadpin_sysctl_path, loadpin_sysctl_table))
266 pr_notice("sysctl registration failed!\n");
268 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
273 DEFINE_LSM(loadpin) = {
275 .init = loadpin_init,
278 #ifdef CONFIG_SECURITY_LOADPIN_VERITY
280 enum loadpin_securityfs_interface_index {
284 static int read_trusted_verity_root_digests(unsigned int fd)
291 if (deny_reading_verity_digests)
294 /* The list of trusted root digests can only be set up once */
295 if (!list_empty(&dm_verity_loadpin_trusted_root_digests))
302 data = kzalloc(SZ_4K, GFP_KERNEL);
308 rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY);
317 while ((d = strsep(&p, "\n")) != NULL) {
319 struct dm_verity_loadpin_trusted_root_digest *trd;
322 /* first line, validate header */
323 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) {
340 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL);
346 if (hex2bin(trd->data, d, len)) {
354 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests);
357 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) {
370 /* any failure in loading/parsing invalidates the entire list */
372 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp;
374 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) {
375 list_del(&trd->node);
380 /* disallow further attempts after reading a corrupt/invalid file */
381 deny_reading_verity_digests = true;
388 /******************************** securityfs ********************************/
390 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
392 void __user *uarg = (void __user *)arg;
396 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS:
397 if (copy_from_user(&fd, uarg, sizeof(fd)))
400 return read_trusted_verity_root_digests(fd);
407 static const struct file_operations loadpin_dm_verity_ops = {
408 .unlocked_ioctl = dm_verity_ioctl,
409 .compat_ioctl = compat_ptr_ioctl,
413 * init_loadpin_securityfs - create the securityfs directory for LoadPin
415 * We can not put this method normally under the loadpin_init() code path since
416 * the security subsystem gets initialized before the vfs caches.
418 * Returns 0 if the securityfs directory creation was successful.
420 static int __init init_loadpin_securityfs(void)
422 struct dentry *loadpin_dir, *dentry;
424 loadpin_dir = securityfs_create_dir("loadpin", NULL);
425 if (IS_ERR(loadpin_dir)) {
426 pr_err("LoadPin: could not create securityfs dir: %ld\n",
427 PTR_ERR(loadpin_dir));
428 return PTR_ERR(loadpin_dir);
431 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir,
432 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops);
433 if (IS_ERR(dentry)) {
434 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n",
436 return PTR_ERR(dentry);
442 fs_initcall(init_loadpin_securityfs);
444 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */
446 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
447 module_param(enforce, int, 0);
448 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning");
449 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0);
450 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types");