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 #ifdef CONFIG_SYSCTL 57 static struct ctl_table loadpin_sysctl_table[] = { 58 { 59 .procname = "enforce", 60 .data = &enforce, 61 .maxlen = sizeof(int), 62 .mode = 0644, 63 .proc_handler = proc_dointvec_minmax, 64 .extra1 = SYSCTL_ONE, 65 .extra2 = SYSCTL_ONE, 66 }, 67 }; 68 69 static void set_sysctl(bool is_writable) 70 { 71 /* 72 * If load pinning is not enforced via a read-only block 73 * device, allow sysctl to change modes for testing. 74 */ 75 if (is_writable) 76 loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO; 77 else 78 loadpin_sysctl_table[0].extra1 = SYSCTL_ONE; 79 } 80 #else 81 static inline void set_sysctl(bool is_writable) { } 82 #endif 83 84 static void report_writable(struct super_block *mnt_sb, bool writable) 85 { 86 if (mnt_sb->s_bdev) { 87 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev, 88 MAJOR(mnt_sb->s_bdev->bd_dev), 89 MINOR(mnt_sb->s_bdev->bd_dev), 90 writable ? "writable" : "read-only"); 91 } else 92 pr_info("mnt_sb lacks block device, treating as: writable\n"); 93 94 if (!writable) 95 pr_info("load pinning engaged.\n"); 96 } 97 98 /* 99 * This must be called after early kernel init, since then the rootdev 100 * is available. 101 */ 102 static bool sb_is_writable(struct super_block *mnt_sb) 103 { 104 bool writable = true; 105 106 if (mnt_sb->s_bdev) 107 writable = !bdev_read_only(mnt_sb->s_bdev); 108 109 return writable; 110 } 111 112 static void loadpin_sb_free_security(struct super_block *mnt_sb) 113 { 114 /* 115 * When unmounting the filesystem we were using for load 116 * pinning, we acknowledge the superblock release, but make sure 117 * no other modules or firmware can be loaded when we are in 118 * enforcing mode. Otherwise, allow the root to be reestablished. 119 */ 120 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 121 if (enforce) { 122 pinned_root = ERR_PTR(-EIO); 123 pr_info("umount pinned fs: refusing further loads\n"); 124 } else { 125 pinned_root = NULL; 126 } 127 } 128 } 129 130 static int loadpin_check(struct file *file, enum kernel_read_file_id id) 131 { 132 struct super_block *load_root; 133 const char *origin = kernel_read_file_id_str(id); 134 bool first_root_pin = false; 135 bool load_root_writable; 136 137 /* If the file id is excluded, ignore the pinning. */ 138 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && 139 ignore_read_file_id[id]) { 140 report_load(origin, file, "pinning-excluded"); 141 return 0; 142 } 143 144 /* This handles the older init_module API that has a NULL file. */ 145 if (!file) { 146 if (!enforce) { 147 report_load(origin, NULL, "old-api-pinning-ignored"); 148 return 0; 149 } 150 151 report_load(origin, NULL, "old-api-denied"); 152 return -EPERM; 153 } 154 155 load_root = file->f_path.mnt->mnt_sb; 156 load_root_writable = sb_is_writable(load_root); 157 158 /* First loaded module/firmware defines the root for all others. */ 159 spin_lock(&pinned_root_spinlock); 160 /* 161 * pinned_root is only NULL at startup or when the pinned root has 162 * been unmounted while we are not in enforcing mode. Otherwise, it 163 * is either a valid reference, or an ERR_PTR. 164 */ 165 if (!pinned_root) { 166 pinned_root = load_root; 167 first_root_pin = true; 168 } 169 spin_unlock(&pinned_root_spinlock); 170 171 if (first_root_pin) { 172 report_writable(pinned_root, load_root_writable); 173 set_sysctl(load_root_writable); 174 report_load(origin, file, "pinned"); 175 } 176 177 if (IS_ERR_OR_NULL(pinned_root) || 178 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) { 179 if (unlikely(!enforce)) { 180 report_load(origin, file, "pinning-ignored"); 181 return 0; 182 } 183 184 report_load(origin, file, "denied"); 185 return -EPERM; 186 } 187 188 return 0; 189 } 190 191 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, 192 bool contents) 193 { 194 /* 195 * LoadPin only cares about the _origin_ of a file, not its 196 * contents, so we can ignore the "are full contents available" 197 * argument here. 198 */ 199 return loadpin_check(file, id); 200 } 201 202 static int loadpin_load_data(enum kernel_load_data_id id, bool contents) 203 { 204 /* 205 * LoadPin only cares about the _origin_ of a file, not its 206 * contents, so a NULL file is passed, and we can ignore the 207 * state of "contents". 208 */ 209 return loadpin_check(NULL, (enum kernel_read_file_id) id); 210 } 211 212 static const struct lsm_id loadpin_lsmid = { 213 .name = "loadpin", 214 .id = LSM_ID_LOADPIN, 215 }; 216 217 static struct security_hook_list loadpin_hooks[] __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), 221 }; 222 223 static void __init parse_exclude(void) 224 { 225 int i, j; 226 char *cur; 227 228 /* 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. 232 */ 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)); 237 238 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { 239 cur = exclude_read_files[i]; 240 if (!cur) 241 break; 242 if (*cur == '\0') 243 continue; 244 245 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; 250 /* 251 * Can not break, because one read_file_str 252 * may map to more than on read_file_id. 253 */ 254 } 255 } 256 } 257 } 258 259 static int __init loadpin_init(void) 260 { 261 pr_info("ready to pin (currently %senforcing)\n", 262 enforce ? "" : "not "); 263 parse_exclude(); 264 #ifdef CONFIG_SYSCTL 265 if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table)) 266 pr_notice("sysctl registration failed!\n"); 267 #endif 268 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), 269 &loadpin_lsmid); 270 271 return 0; 272 } 273 274 #ifdef CONFIG_SECURITY_LOADPIN_VERITY 275 276 enum loadpin_securityfs_interface_index { 277 LOADPIN_DM_VERITY, 278 }; 279 280 static int read_trusted_verity_root_digests(unsigned int fd) 281 { 282 void *data; 283 int rc; 284 char *p, *d; 285 286 if (deny_reading_verity_digests) 287 return -EPERM; 288 289 /* The list of trusted root digests can only be set up once */ 290 if (!list_empty(&dm_verity_loadpin_trusted_root_digests)) 291 return -EPERM; 292 293 CLASS(fd, f)(fd); 294 if (fd_empty(f)) 295 return -EINVAL; 296 297 data = kzalloc(SZ_4K, GFP_KERNEL); 298 if (!data) { 299 rc = -ENOMEM; 300 goto err; 301 } 302 303 rc = kernel_read_file(fd_file(f), 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY); 304 if (rc < 0) 305 goto err; 306 307 p = data; 308 p[rc] = '\0'; 309 p = strim(p); 310 311 p = strim(data); 312 while ((d = strsep(&p, "\n")) != NULL) { 313 int len; 314 struct dm_verity_loadpin_trusted_root_digest *trd; 315 316 if (d == data) { 317 /* first line, validate header */ 318 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) { 319 rc = -EPROTO; 320 goto err; 321 } 322 323 continue; 324 } 325 326 len = strlen(d); 327 328 if (len % 2) { 329 rc = -EPROTO; 330 goto err; 331 } 332 333 len /= 2; 334 335 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL); 336 if (!trd) { 337 rc = -ENOMEM; 338 goto err; 339 } 340 trd->len = len; 341 342 if (hex2bin(trd->data, d, len)) { 343 kfree(trd); 344 rc = -EPROTO; 345 goto err; 346 } 347 348 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests); 349 } 350 351 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) { 352 rc = -EPROTO; 353 goto err; 354 } 355 356 kfree(data); 357 358 return 0; 359 360 err: 361 kfree(data); 362 363 /* any failure in loading/parsing invalidates the entire list */ 364 { 365 struct dm_verity_loadpin_trusted_root_digest *trd, *tmp; 366 367 list_for_each_entry_safe(trd, tmp, &dm_verity_loadpin_trusted_root_digests, node) { 368 list_del(&trd->node); 369 kfree(trd); 370 } 371 } 372 373 /* disallow further attempts after reading a corrupt/invalid file */ 374 deny_reading_verity_digests = true; 375 376 return rc; 377 } 378 379 /******************************** securityfs ********************************/ 380 381 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) 382 { 383 void __user *uarg = (void __user *)arg; 384 unsigned int fd; 385 386 switch (cmd) { 387 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS: 388 if (copy_from_user(&fd, uarg, sizeof(fd))) 389 return -EFAULT; 390 391 return read_trusted_verity_root_digests(fd); 392 393 default: 394 return -EINVAL; 395 } 396 } 397 398 static const struct file_operations loadpin_dm_verity_ops = { 399 .unlocked_ioctl = dm_verity_ioctl, 400 .compat_ioctl = compat_ptr_ioctl, 401 }; 402 403 /** 404 * init_loadpin_securityfs - create the securityfs directory for LoadPin 405 * 406 * We can not put this method normally under the loadpin_init() code path since 407 * the security subsystem gets initialized before the vfs caches. 408 * 409 * Returns 0 if the securityfs directory creation was successful. 410 */ 411 static int __init init_loadpin_securityfs(void) 412 { 413 struct dentry *loadpin_dir, *dentry; 414 415 loadpin_dir = securityfs_create_dir("loadpin", NULL); 416 if (IS_ERR(loadpin_dir)) { 417 pr_err("LoadPin: could not create securityfs dir: %ld\n", 418 PTR_ERR(loadpin_dir)); 419 return PTR_ERR(loadpin_dir); 420 } 421 422 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir, 423 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops); 424 if (IS_ERR(dentry)) { 425 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n", 426 PTR_ERR(dentry)); 427 return PTR_ERR(dentry); 428 } 429 430 return 0; 431 } 432 433 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */ 434 435 DEFINE_LSM(loadpin) = { 436 .id = &loadpin_lsmid, 437 .init = loadpin_init, 438 #ifdef CONFIG_SECURITY_LOADPIN_VERITY 439 .initcall_fs = init_loadpin_securityfs, 440 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */ 441 }; 442 443 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 444 module_param(enforce, int, 0); 445 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 446 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); 447 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); 448