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 static struct ctl_table loadpin_sysctl_table[] = { 56 { 57 .procname = "enforce", 58 .data = &enforce, 59 .maxlen = sizeof(int), 60 .mode = 0644, 61 .proc_handler = proc_dointvec_minmax, 62 .extra1 = SYSCTL_ONE, 63 .extra2 = SYSCTL_ONE, 64 }, 65 { } 66 }; 67 68 static void set_sysctl(bool is_writable) 69 { 70 /* 71 * If load pinning is not enforced via a read-only block 72 * device, allow sysctl to change modes for testing. 73 */ 74 if (is_writable) 75 loadpin_sysctl_table[0].extra1 = SYSCTL_ZERO; 76 else 77 loadpin_sysctl_table[0].extra1 = SYSCTL_ONE; 78 } 79 #else 80 static inline void set_sysctl(bool is_writable) { } 81 #endif 82 83 static void report_writable(struct super_block *mnt_sb, bool writable) 84 { 85 if (mnt_sb->s_bdev) { 86 pr_info("%pg (%u:%u): %s\n", mnt_sb->s_bdev, 87 MAJOR(mnt_sb->s_bdev->bd_dev), 88 MINOR(mnt_sb->s_bdev->bd_dev), 89 writable ? "writable" : "read-only"); 90 } else 91 pr_info("mnt_sb lacks block device, treating as: writable\n"); 92 93 if (!writable) 94 pr_info("load pinning engaged.\n"); 95 } 96 97 /* 98 * This must be called after early kernel init, since then the rootdev 99 * is available. 100 */ 101 static bool sb_is_writable(struct super_block *mnt_sb) 102 { 103 bool writable = true; 104 105 if (mnt_sb->s_bdev) 106 writable = !bdev_read_only(mnt_sb->s_bdev); 107 108 return writable; 109 } 110 111 static void loadpin_sb_free_security(struct super_block *mnt_sb) 112 { 113 /* 114 * When unmounting the filesystem we were using for load 115 * pinning, we acknowledge the superblock release, but make sure 116 * no other modules or firmware can be loaded when we are in 117 * enforcing mode. Otherwise, allow the root to be reestablished. 118 */ 119 if (!IS_ERR_OR_NULL(pinned_root) && mnt_sb == pinned_root) { 120 if (enforce) { 121 pinned_root = ERR_PTR(-EIO); 122 pr_info("umount pinned fs: refusing further loads\n"); 123 } else { 124 pinned_root = NULL; 125 } 126 } 127 } 128 129 static int loadpin_check(struct file *file, enum kernel_read_file_id id) 130 { 131 struct super_block *load_root; 132 const char *origin = kernel_read_file_id_str(id); 133 bool first_root_pin = false; 134 bool load_root_writable; 135 136 /* If the file id is excluded, ignore the pinning. */ 137 if ((unsigned int)id < ARRAY_SIZE(ignore_read_file_id) && 138 ignore_read_file_id[id]) { 139 report_load(origin, file, "pinning-excluded"); 140 return 0; 141 } 142 143 /* This handles the older init_module API that has a NULL file. */ 144 if (!file) { 145 if (!enforce) { 146 report_load(origin, NULL, "old-api-pinning-ignored"); 147 return 0; 148 } 149 150 report_load(origin, NULL, "old-api-denied"); 151 return -EPERM; 152 } 153 154 load_root = file->f_path.mnt->mnt_sb; 155 load_root_writable = sb_is_writable(load_root); 156 157 /* First loaded module/firmware defines the root for all others. */ 158 spin_lock(&pinned_root_spinlock); 159 /* 160 * pinned_root is only NULL at startup or when the pinned root has 161 * been unmounted while we are not in enforcing mode. Otherwise, it 162 * is either a valid reference, or an ERR_PTR. 163 */ 164 if (!pinned_root) { 165 pinned_root = load_root; 166 first_root_pin = true; 167 } 168 spin_unlock(&pinned_root_spinlock); 169 170 if (first_root_pin) { 171 report_writable(pinned_root, load_root_writable); 172 set_sysctl(load_root_writable); 173 report_load(origin, file, "pinned"); 174 } 175 176 if (IS_ERR_OR_NULL(pinned_root) || 177 ((load_root != pinned_root) && !dm_verity_loadpin_is_bdev_trusted(load_root->s_bdev))) { 178 if (unlikely(!enforce)) { 179 report_load(origin, file, "pinning-ignored"); 180 return 0; 181 } 182 183 report_load(origin, file, "denied"); 184 return -EPERM; 185 } 186 187 return 0; 188 } 189 190 static int loadpin_read_file(struct file *file, enum kernel_read_file_id id, 191 bool contents) 192 { 193 /* 194 * LoadPin only cares about the _origin_ of a file, not its 195 * contents, so we can ignore the "are full contents available" 196 * argument here. 197 */ 198 return loadpin_check(file, id); 199 } 200 201 static int loadpin_load_data(enum kernel_load_data_id id, bool contents) 202 { 203 /* 204 * LoadPin only cares about the _origin_ of a file, not its 205 * contents, so a NULL file is passed, and we can ignore the 206 * state of "contents". 207 */ 208 return loadpin_check(NULL, (enum kernel_read_file_id) id); 209 } 210 211 static struct security_hook_list loadpin_hooks[] __ro_after_init = { 212 LSM_HOOK_INIT(sb_free_security, loadpin_sb_free_security), 213 LSM_HOOK_INIT(kernel_read_file, loadpin_read_file), 214 LSM_HOOK_INIT(kernel_load_data, loadpin_load_data), 215 }; 216 217 static void __init parse_exclude(void) 218 { 219 int i, j; 220 char *cur; 221 222 /* 223 * Make sure all the arrays stay within expected sizes. This 224 * is slightly weird because kernel_read_file_str[] includes 225 * READING_MAX_ID, which isn't actually meaningful here. 226 */ 227 BUILD_BUG_ON(ARRAY_SIZE(exclude_read_files) != 228 ARRAY_SIZE(ignore_read_file_id)); 229 BUILD_BUG_ON(ARRAY_SIZE(kernel_read_file_str) < 230 ARRAY_SIZE(ignore_read_file_id)); 231 232 for (i = 0; i < ARRAY_SIZE(exclude_read_files); i++) { 233 cur = exclude_read_files[i]; 234 if (!cur) 235 break; 236 if (*cur == '\0') 237 continue; 238 239 for (j = 0; j < ARRAY_SIZE(ignore_read_file_id); j++) { 240 if (strcmp(cur, kernel_read_file_str[j]) == 0) { 241 pr_info("excluding: %s\n", 242 kernel_read_file_str[j]); 243 ignore_read_file_id[j] = 1; 244 /* 245 * Can not break, because one read_file_str 246 * may map to more than on read_file_id. 247 */ 248 } 249 } 250 } 251 } 252 253 static int __init loadpin_init(void) 254 { 255 pr_info("ready to pin (currently %senforcing)\n", 256 enforce ? "" : "not "); 257 parse_exclude(); 258 #ifdef CONFIG_SYSCTL 259 if (!register_sysctl("kernel/loadpin", loadpin_sysctl_table)) 260 pr_notice("sysctl registration failed!\n"); 261 #endif 262 security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin"); 263 264 return 0; 265 } 266 267 DEFINE_LSM(loadpin) = { 268 .name = "loadpin", 269 .init = loadpin_init, 270 }; 271 272 #ifdef CONFIG_SECURITY_LOADPIN_VERITY 273 274 enum loadpin_securityfs_interface_index { 275 LOADPIN_DM_VERITY, 276 }; 277 278 static int read_trusted_verity_root_digests(unsigned int fd) 279 { 280 struct fd f; 281 void *data; 282 int rc; 283 char *p, *d; 284 285 if (deny_reading_verity_digests) 286 return -EPERM; 287 288 /* The list of trusted root digests can only be set up once */ 289 if (!list_empty(&dm_verity_loadpin_trusted_root_digests)) 290 return -EPERM; 291 292 f = fdget(fd); 293 if (!f.file) 294 return -EINVAL; 295 296 data = kzalloc(SZ_4K, GFP_KERNEL); 297 if (!data) { 298 rc = -ENOMEM; 299 goto err; 300 } 301 302 rc = kernel_read_file(f.file, 0, (void **)&data, SZ_4K - 1, NULL, READING_POLICY); 303 if (rc < 0) 304 goto err; 305 306 p = data; 307 p[rc] = '\0'; 308 p = strim(p); 309 310 p = strim(data); 311 while ((d = strsep(&p, "\n")) != NULL) { 312 int len; 313 struct dm_verity_loadpin_trusted_root_digest *trd; 314 315 if (d == data) { 316 /* first line, validate header */ 317 if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) { 318 rc = -EPROTO; 319 goto err; 320 } 321 322 continue; 323 } 324 325 len = strlen(d); 326 327 if (len % 2) { 328 rc = -EPROTO; 329 goto err; 330 } 331 332 len /= 2; 333 334 trd = kzalloc(struct_size(trd, data, len), GFP_KERNEL); 335 if (!trd) { 336 rc = -ENOMEM; 337 goto err; 338 } 339 trd->len = len; 340 341 if (hex2bin(trd->data, d, len)) { 342 kfree(trd); 343 rc = -EPROTO; 344 goto err; 345 } 346 347 list_add_tail(&trd->node, &dm_verity_loadpin_trusted_root_digests); 348 } 349 350 if (list_empty(&dm_verity_loadpin_trusted_root_digests)) { 351 rc = -EPROTO; 352 goto err; 353 } 354 355 kfree(data); 356 fdput(f); 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 fdput(f); 377 378 return rc; 379 } 380 381 /******************************** securityfs ********************************/ 382 383 static long dm_verity_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) 384 { 385 void __user *uarg = (void __user *)arg; 386 unsigned int fd; 387 388 switch (cmd) { 389 case LOADPIN_IOC_SET_TRUSTED_VERITY_DIGESTS: 390 if (copy_from_user(&fd, uarg, sizeof(fd))) 391 return -EFAULT; 392 393 return read_trusted_verity_root_digests(fd); 394 395 default: 396 return -EINVAL; 397 } 398 } 399 400 static const struct file_operations loadpin_dm_verity_ops = { 401 .unlocked_ioctl = dm_verity_ioctl, 402 .compat_ioctl = compat_ptr_ioctl, 403 }; 404 405 /** 406 * init_loadpin_securityfs - create the securityfs directory for LoadPin 407 * 408 * We can not put this method normally under the loadpin_init() code path since 409 * the security subsystem gets initialized before the vfs caches. 410 * 411 * Returns 0 if the securityfs directory creation was successful. 412 */ 413 static int __init init_loadpin_securityfs(void) 414 { 415 struct dentry *loadpin_dir, *dentry; 416 417 loadpin_dir = securityfs_create_dir("loadpin", NULL); 418 if (IS_ERR(loadpin_dir)) { 419 pr_err("LoadPin: could not create securityfs dir: %ld\n", 420 PTR_ERR(loadpin_dir)); 421 return PTR_ERR(loadpin_dir); 422 } 423 424 dentry = securityfs_create_file("dm-verity", 0600, loadpin_dir, 425 (void *)LOADPIN_DM_VERITY, &loadpin_dm_verity_ops); 426 if (IS_ERR(dentry)) { 427 pr_err("LoadPin: could not create securityfs entry 'dm-verity': %ld\n", 428 PTR_ERR(dentry)); 429 return PTR_ERR(dentry); 430 } 431 432 return 0; 433 } 434 435 fs_initcall(init_loadpin_securityfs); 436 437 #endif /* CONFIG_SECURITY_LOADPIN_VERITY */ 438 439 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */ 440 module_param(enforce, int, 0); 441 MODULE_PARM_DESC(enforce, "Enforce module/firmware pinning"); 442 module_param_array_named(exclude, exclude_read_files, charp, NULL, 0); 443 MODULE_PARM_DESC(exclude, "Exclude pinning specific read file types"); 444