security/loadpin/loadpin.c

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