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