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/hex.h> 15 #include <linux/kernel_read_file.h> 16 #include <linux/lsm_hooks.h> 17 #include <linux/mount.h> 18 #include <linux/blkdev.h> 19 #include <linux/path.h> 20 #include <linux/sched.h> /* current */ 21 #include <linux/string_helpers.h> 22 #include <linux/dm-verity-loadpin.h> 23 #include <uapi/linux/loadpin.h> 24 #include <uapi/linux/lsm.h> 25 26 #define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS" 27 28 static void report_load(const char *origin, struct file *file, char *operation) 29 { 30 char *cmdline, *pathname; 31 32 pathname = kstrdup_quotable_file(file, GFP_KERNEL); 33 cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL); 34 35 pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n", 36 origin, operation, 37 (pathname && pathname[0] != '<') ? "\"" : "", 38 pathname, 39 (pathname && pathname[0] != '<') ? "\"" : "", 40 task_pid_nr(current), 41 cmdline ? "\"" : "", cmdline, cmdline ? "\"" : ""); 42 43 kfree(cmdline); 44 kfree(pathname); 45 } 46 47 static int enforce = IS_ENABLED(CONFIG_SECURITY_LOADPIN_ENFORCE); 48 static char *exclude_read_files[READING_MAX_ID]; 49 static int ignore_read_file_id[READING_MAX_ID] __ro_after_init; 50 static struct super_block *pinned_root; 51 static DEFINE_SPINLOCK(pinned_root_spinlock); 52 #ifdef CONFIG_SECURITY_LOADPIN_VERITY 53 static bool deny_reading_verity_digests; 54 #endif 55 56 // initialized to false 57 static bool loadpin_root_writable; 58 #ifdef CONFIG_SYSCTL 59 60 static int proc_handler_loadpin(const struct ctl_table *table, int dir, 61 void *buffer, size_t *lenp, loff_t *ppos) 62 { 63 if (!loadpin_root_writable && SYSCTL_USER_TO_KERN(dir)) 64 return -EINVAL; 65 return proc_dointvec_minmax(table, dir, buffer, lenp, ppos); 66 } 67 68 static const struct ctl_table loadpin_sysctl_table[] = { 69 { 70 .procname = "enforce", 71 .data = &enforce, 72 .maxlen = sizeof(int), 73 .mode = 0644, 74 .proc_handler = proc_handler_loadpin, 75 .extra1 = SYSCTL_ZERO, 76 .extra2 = SYSCTL_ONE, 77 }, 78 }; 79 #endif 80 81 static void report_writable(struct super_block *mnt_sb, bool writable) 82 { 83 if (mnt_sb->s_bdev) { 84 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev, 85 MAJOR(mnt_sb->s_bdev->bd_dev), 86 MINOR(mnt_sb->s_bdev->bd_dev), 87 writable ? "writable" : "read-only"); 88 } else 89 pr_info("mnt_sb lacks block device, treating as: writable\n"); 90 91 if (!writable) 92 pr_info("load pinning engaged.\n"); 93 } 94 95 /* 96 * This must be called after early kernel init, since then the rootdev 97 * is available. 98 */ 99 static bool sb_is_writable(struct super_block *mnt_sb) 100 { 101 bool writable = true; 102 103 if (mnt_sb->s_bdev) 104 writable = !bdev_read_only(mnt_sb->s_bdev); 105 106 return writable; 107 } 108 109 static void loadpin_sb_free_security(struct super_block *mnt_sb) 110 { 111 /* 112 * When unmounting the filesystem we were using for load 113 * pinning, we acknowledge the superblock release, but make sure 114 * no other modules or firmware can be loaded when we are in 115 * enforcing mode. Otherwise, allow the root to be reestablished. 116 */ 117 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 118 if (enforce) { 119 pinned_root = ERR_PTR(-EIO); 120 pr_info("umount pinned fs: refusing further loads\n"); 121 } else { 122 pinned_root = NULL; 123 } 124 } 125 } 126 127 static int loadpin_check(struct file *file, enum kernel_read_file_id id) 128 { 129 struct super_block *load_root; 130 const char *origin = kernel_read_file_id_str(id); 131 bool first_root_pin = false; 132 133 /* If the file id is excluded, ignore the pinning. */ 134 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && 135 ignore_read_file_id[id]) { 136 report_load(origin, file, "pinning-excluded"); 137 return 0; 138 } 139 140 /* This handles the older init_module API that has a NULL file. */ 141 if (!file) { 142 if (!enforce) { 143 report_load(origin, NULL, "old-api-pinning-ignored"); 144 return 0; 145 } 146 147 report_load(origin, NULL, "old-api-denied"); 148 return -EPERM; 149 } 150 151 load_root = file->f_path.mnt->mnt_sb; 152 153 /* First loaded module/firmware defines the root for all others. */ 154 spin_lock(&pinned_root_spinlock); 155 /* 156 * pinned_root is only NULL at startup or when the pinned root has 157 * been unmounted while we are not in enforcing mode. Otherwise, it 158 * is either a valid reference, or an ERR_PTR. 159 */ 160 if (!pinned_root) { 161 pinned_root = load_root; 162 first_root_pin = true; 163 } 164 spin_unlock(&pinned_root_spinlock); 165 166 if (first_root_pin) { 167 loadpin_root_writable = sb_is_writable(pinned_root); 168 report_writable(pinned_root, loadpin_root_writable); 169 report_load(origin, file, "pinned"); 170 } 171 172 if (IS_ERR_OR_NULL(pinned_root) || 173 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) { 174 if (unlikely(!enforce)) { 175 report_load(origin, file, "pinning-ignored"); 176 return 0; 177 } 178 179 report_load(origin, file, "denied"); 180 return -EPERM; 181 } 182 183 return 0; 184 } 185 186 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, 187 bool contents) 188 { 189 /* 190 * LoadPin only cares about the _origin_ of a file, not its 191 * contents, so we can ignore the "are full contents available" 192 * argument here. 193 */ 194 return loadpin_check(file, id); 195 } 196 197 static int loadpin_load_data(enum kernel_load_data_id id, bool contents) 198 { 199 /* 200 * LoadPin only cares about the _origin_ of a file, not its 201 * contents, so a NULL file is passed, and we can ignore the 202 * state of "contents". 203 */ 204 return loadpin_check(NULL, (enum kernel_read_file_id) id); 205 } 206 207 static const struct lsm_id loadpin_lsmid = { 208 .name = "loadpin", 209 .id = LSM_ID_LOADPIN, 210 }; 211 212 static struct security_hook_list loadpin_hooks[] __ro_after_init = { 213 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 214 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 215 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 216 }; 217 218 static void __init parse_exclude(void) 219 { 220 int i, j; 221 char *cur; 222 223 /* 224 * Make sure all the arrays stay within expected sizes. This 225 * is slightly weird because kernel_read_file_str[] includes 226 * READING_MAX_ID, which isn't actually meaningful here. 227 */ 228 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) != 229 ARRAY_SIZE(ignore_read_file_id)); 230 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < 231 ARRAY_SIZE(ignore_read_file_id)); 232 233 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { 234 cur = exclude_read_files[i]; 235 if (!cur) 236 break; 237 if (*cur == '\0') 238 continue; 239 240 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) { 241 if (strcmp(cur, kernel_read_file_str[j]) == 0) { 242 pr_info("excluding: %s\n", 243 kernel_read_file_str[j]); 244 ignore_read_file_id[j] = 1; 245 /* 246 * Can not break, because one read_file_str 247 * may map to more than on read_file_id. 248 */ 249 } 250 } 251 } 252 } 253 254 static int __init loadpin_init(void) 255 { 256 pr_info("ready to pin (currently %senforcing)\n", 257 enforce ? "" : "not "); 258 parse_exclude(); 259 #ifdef CONFIG_SYSCTL 260 if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table)) 261 pr_notice("sysctl registration failed!\n"); 262 #endif 263 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), 264 &loadpin_lsmid); 265 266 return 0; 267 } 268 269 #ifdef CONFIG_SECURITY_LOADPIN_VERITY 270 271 enum loadpin_securityfs_interface_index { 272 LOADPIN_DM_VERITY, 273 }; 274 275 static int read_trusted_verity_root_digests(unsigned int fd) 276 { 277 void *data; 278 int rc; 279 char *p, *d; 280 281 if (deny_reading_verity_digests) 282 return -EPERM; 283 284 /* The list of trusted root digests can only be set up once */ 285 if (!list_empty(&dm_verity_loadpin_trusted_root_digests)) 286 return -EPERM; 287 288 CLASS(fd, f)(fd); 289 if (fd_empty(f)) 290 return -EINVAL; 291 292 data = kzalloc(SZ_4K, GFP_KERNEL); 293 if (!data) { 294 rc = -ENOMEM; 295 goto err; 296 } 297 298 rc = kernel_read_file(fd_file(f), 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY); 299 if (rc < 0) 300 goto err; 301 302 p = data; 303 p[rc] = '\0'; 304 p = strim(p); 305 306 p = strim(data); 307 while ((d = strsep(&p, "\n")) != NULL) { 308 int len; 309 struct dm_verity_loadpin_trusted_root_digest *trd; 310 311 if (d == data) { 312 /* first line, validate header */ 313 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) { 314 rc = -EPROTO; 315 goto err; 316 } 317 318 continue; 319 } 320 321 len = strlen(d); 322 323 if (len % 2) { 324 rc = -EPROTO; 325 goto err; 326 } 327 328 len /= 2; 329 330 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL); 331 if (!trd) { 332 rc = -ENOMEM; 333 goto err; 334 } 335 trd->len = len; 336 337 if (hex2bin(trd->data, d, len)) { 338 kfree(trd); 339 rc = -EPROTO; 340 goto err; 341 } 342 343 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests); 344 } 345 346 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) { 347 rc = -EPROTO; 348 goto err; 349 } 350 351 kfree(data); 352 353 return 0; 354 355 err: 356 kfree(data); 357 358 /* any failure in loading/parsing invalidates the entire list */ 359 { 360 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp; 361 362 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) { 363 list_del(&trd->node); 364 kfree(trd); 365 } 366 } 367 368 /* disallow further attempts after reading a corrupt/invalid file */ 369 deny_reading_verity_digests = true; 370 371 return rc; 372 } 373 374 /******************************** securityfs ********************************/ 375 376 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) 377 { 378 void __user *uarg = (void __user *)arg; 379 unsigned int fd; 380 381 switch (cmd) { 382 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS: 383 if (copy_from_user(&fd, uarg, sizeof(fd))) 384 return -EFAULT; 385 386 return read_trusted_verity_root_digests(fd); 387 388 default: 389 return -EINVAL; 390 } 391 } 392 393 static const struct file_operations loadpin_dm_verity_ops = { 394 .unlocked_ioctl = dm_verity_ioctl, 395 .compat_ioctl = compat_ptr_ioctl, 396 }; 397 398 /** 399 * init_loadpin_securityfs - create the securityfs directory for LoadPin 400 * 401 * We can not put this method normally under the loadpin_init() code path since 402 * the security subsystem gets initialized before the vfs caches. 403 * 404 * Returns 0 if the securityfs directory creation was successful. 405 */ 406 static int __init init_loadpin_securityfs(void) 407 { 408 struct dentry *loadpin_dir, *dentry; 409 410 loadpin_dir = securityfs_create_dir("loadpin", NULL); 411 if (IS_ERR(loadpin_dir)) { 412 pr_err("LoadPin: could not create securityfs dir: %ld\n", 413 PTR_ERR(loadpin_dir)); 414 return PTR_ERR(loadpin_dir); 415 } 416 417 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir, 418 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops); 419 if (IS_ERR(dentry)) { 420 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n", 421 PTR_ERR(dentry)); 422 return PTR_ERR(dentry); 423 } 424 425 return 0; 426 } 427 428 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */ 429 430 DEFINE_LSM(loadpin) = { 431 .id = &loadpin_lsmid, 432 .init = loadpin_init, 433 #ifdef CONFIG_SECURITY_LOADPIN_VERITY 434 .initcall_fs = init_loadpin_securityfs, 435 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */ 436 }; 437 438 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 439 module_param(enforce, int, 0); 440 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 441 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); 442 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); 443