kernel/jump_label.c

   1 /*
   2  * jump label support
   3  *
   4  * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
   5  * Copyright (C) 2011 Peter Zijlstra
   6  *
   7  */
   8 #include <linux/memory.h>
   9 #include <linux/uaccess.h>
  10 #include <linux/module.h>
  11 #include <linux/list.h>
  12 #include <linux/slab.h>
  13 #include <linux/sort.h>
  14 #include <linux/err.h>
  15 #include <linux/static_key.h>
  16 #include <linux/jump_label_ratelimit.h>
  17 #include <linux/bug.h>
  18
  19 #ifdef HAVE_JUMP_LABEL
  20
  21 /* mutex to protect coming/going of the the jump_label table */
  22 static DEFINE_MUTEX(jump_label_mutex);
  23
  24 void jump_label_lock(void)
  25 {
  26         mutex_lock(&jump_label_mutex);
  27 }
  28
  29 void jump_label_unlock(void)
  30 {
  31         mutex_unlock(&jump_label_mutex);
  32 }
  33
  34 static int jump_label_cmp(const void *a, const void *b)
  35 {
  36         const struct jump_entry *jea = a;
  37         const struct jump_entry *jeb = b;
  38
  39         if (jea->key < jeb->key)
  40                 return -1;
  41
  42         if (jea->key > jeb->key)
  43                 return 1;
  44
  45         return 0;
  46 }
  47
  48 static void
  49 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
  50 {
  51         unsigned long size;
  52
  53         size = (((unsigned long)stop - (unsigned long)start)
  54                                         / sizeof(struct jump_entry));
  55         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  56 }
  57
  58 static void jump_label_update(struct static_key *key);
  59
  60 /*
  61  * There are similar definitions for the !HAVE_JUMP_LABEL case in jump_label.h.
  62  * The use of 'atomic_read()' requires atomic.h and its problematic for some
  63  * kernel headers such as kernel.h and others. Since static_key_count() is not
  64  * used in the branch statements as it is for the !HAVE_JUMP_LABEL case its ok
  65  * to have it be a function here. Similarly, for 'static_key_enable()' and
  66  * 'static_key_disable()', which require bug.h. This should allow jump_label.h
  67  * to be included from most/all places for HAVE_JUMP_LABEL.
  68  */
  69 int static_key_count(struct static_key *key)
  70 {
  71         /*
  72          * -1 means the first static_key_slow_inc() is in progress.
  73          *  static_key_enabled() must return true, so return 1 here.
  74          */
  75         int n = atomic_read(&key->enabled);
  76
  77         return n >= 0 ? n : 1;
  78 }
  79 EXPORT_SYMBOL_GPL(static_key_count);
  80
  81 void static_key_enable(struct static_key *key)
  82 {
  83         int count = static_key_count(key);
  84
  85         WARN_ON_ONCE(count < 0 || count > 1);
  86
  87         if (!count)
  88                 static_key_slow_inc(key);
  89 }
  90 EXPORT_SYMBOL_GPL(static_key_enable);
  91
  92 void static_key_disable(struct static_key *key)
  93 {
  94         int count = static_key_count(key);
  95
  96         WARN_ON_ONCE(count < 0 || count > 1);
  97
  98         if (count)
  99                 static_key_slow_dec(key);
 100 }
 101 EXPORT_SYMBOL_GPL(static_key_disable);
 102
 103 void static_key_slow_inc(struct static_key *key)
 104 {
 105         int v, v1;
 106
 107         STATIC_KEY_CHECK_USE();
 108
 109         /*
 110          * Careful if we get concurrent static_key_slow_inc() calls;
 111          * later calls must wait for the first one to _finish_ the
 112          * jump_label_update() process.  At the same time, however,
 113          * the jump_label_update() call below wants to see
 114          * static_key_enabled(&key) for jumps to be updated properly.
 115          *
 116          * So give a special meaning to negative key->enabled: it sends
 117          * static_key_slow_inc() down the slow path, and it is non-zero
 118          * so it counts as "enabled" in jump_label_update().  Note that
 119          * atomic_inc_unless_negative() checks >= 0, so roll our own.
 120          */
 121         for (v = atomic_read(&key->enabled); v > 0; v = v1) {
 122                 v1 = atomic_cmpxchg(&key->enabled, v, v + 1);
 123                 if (likely(v1 == v))
 124                         return;
 125         }
 126
 127         jump_label_lock();
 128         if (atomic_read(&key->enabled) == 0) {
 129                 atomic_set(&key->enabled, -1);
 130                 jump_label_update(key);
 131                 atomic_set(&key->enabled, 1);
 132         } else {
 133                 atomic_inc(&key->enabled);
 134         }
 135         jump_label_unlock();
 136 }
 137 EXPORT_SYMBOL_GPL(static_key_slow_inc);
 138
 139 static void __static_key_slow_dec(struct static_key *key,
 140                 unsigned long rate_limit, struct delayed_work *work)
 141 {
 142         /*
 143          * The negative count check is valid even when a negative
 144          * key->enabled is in use by static_key_slow_inc(); a
 145          * __static_key_slow_dec() before the first static_key_slow_inc()
 146          * returns is unbalanced, because all other static_key_slow_inc()
 147          * instances block while the update is in progress.
 148          */
 149         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
 150                 WARN(atomic_read(&key->enabled) < 0,
 151                      "jump label: negative count!\n");
 152                 return;
 153         }
 154
 155         if (rate_limit) {
 156                 atomic_inc(&key->enabled);
 157                 schedule_delayed_work(work, rate_limit);
 158         } else {
 159                 jump_label_update(key);
 160         }
 161         jump_label_unlock();
 162 }
 163
 164 static void jump_label_update_timeout(struct work_struct *work)
 165 {
 166         struct static_key_deferred *key =
 167                 container_of(work, struct static_key_deferred, work.work);
 168         __static_key_slow_dec(&key->key, 0, NULL);
 169 }
 170
 171 void static_key_slow_dec(struct static_key *key)
 172 {
 173         STATIC_KEY_CHECK_USE();
 174         __static_key_slow_dec(key, 0, NULL);
 175 }
 176 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 177
 178 void static_key_slow_dec_deferred(struct static_key_deferred *key)
 179 {
 180         STATIC_KEY_CHECK_USE();
 181         __static_key_slow_dec(&key->key, key->timeout, &key->work);
 182 }
 183 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 184
 185 void jump_label_rate_limit(struct static_key_deferred *key,
 186                 unsigned long rl)
 187 {
 188         STATIC_KEY_CHECK_USE();
 189         key->timeout = rl;
 190         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 191 }
 192 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 193
 194 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 195 {
 196         if (entry->code <= (unsigned long)end &&
 197                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 198                 return 1;
 199
 200         return 0;
 201 }
 202
 203 static int __jump_label_text_reserved(struct jump_entry *iter_start,
 204                 struct jump_entry *iter_stop, void *start, void *end)
 205 {
 206         struct jump_entry *iter;
 207
 208         iter = iter_start;
 209         while (iter < iter_stop) {
 210                 if (addr_conflict(iter, start, end))
 211                         return 1;
 212                 iter++;
 213         }
 214
 215         return 0;
 216 }
 217
 218 /*
 219  * Update code which is definitely not currently executing.
 220  * Architectures which need heavyweight synchronization to modify
 221  * running code can override this to make the non-live update case
 222  * cheaper.
 223  */
 224 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 225                                             enum jump_label_type type)
 226 {
 227         arch_jump_label_transform(entry, type);
 228 }
 229
 230 static inline struct jump_entry *static_key_entries(struct static_key *key)
 231 {
 232         return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
 233 }
 234
 235 static inline bool static_key_type(struct static_key *key)
 236 {
 237         return (unsigned long)key->entries & JUMP_TYPE_MASK;
 238 }
 239
 240 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
 241 {
 242         return (struct static_key *)((unsigned long)entry->key & ~1UL);
 243 }
 244
 245 static bool jump_entry_branch(struct jump_entry *entry)
 246 {
 247         return (unsigned long)entry->key & 1UL;
 248 }
 249
 250 static enum jump_label_type jump_label_type(struct jump_entry *entry)
 251 {
 252         struct static_key *key = jump_entry_key(entry);
 253         bool enabled = static_key_enabled(key);
 254         bool branch = jump_entry_branch(entry);
 255
 256         /* See the comment in linux/jump_label.h */
 257         return enabled ^ branch;
 258 }
 259
 260 static void __jump_label_update(struct static_key *key,
 261                                 struct jump_entry *entry,
 262                                 struct jump_entry *stop)
 263 {
 264         for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
 265                 /*
 266                  * entry->code set to 0 invalidates module init text sections
 267                  * kernel_text_address() verifies we are not in core kernel
 268                  * init code, see jump_label_invalidate_module_init().
 269                  */
 270                 if (entry->code && kernel_text_address(entry->code))
 271                         arch_jump_label_transform(entry, jump_label_type(entry));
 272         }
 273 }
 274
 275 void __init jump_label_init(void)
 276 {
 277         struct jump_entry *iter_start = __start___jump_table;
 278         struct jump_entry *iter_stop = __stop___jump_table;
 279         struct static_key *key = NULL;
 280         struct jump_entry *iter;
 281
 282         /*
 283          * Since we are initializing the static_key.enabled field with
 284          * with the 'raw' int values (to avoid pulling in atomic.h) in
 285          * jump_label.h, let's make sure that is safe. There are only two
 286          * cases to check since we initialize to 0 or 1.
 287          */
 288         BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
 289         BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);
 290
 291         jump_label_lock();
 292         jump_label_sort_entries(iter_start, iter_stop);
 293
 294         for (iter = iter_start; iter < iter_stop; iter++) {
 295                 struct static_key *iterk;
 296
 297                 /* rewrite NOPs */
 298                 if (jump_label_type(iter) == JUMP_LABEL_NOP)
 299                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 300
 301                 iterk = jump_entry_key(iter);
 302                 if (iterk == key)
 303                         continue;
 304
 305                 key = iterk;
 306                 /*
 307                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 308                  */
 309                 *((unsigned long *)&key->entries) += (unsigned long)iter;
 310 #ifdef CONFIG_MODULES
 311                 key->next = NULL;
 312 #endif
 313         }
 314         static_key_initialized = true;
 315         jump_label_unlock();
 316 }
 317
 318 #ifdef CONFIG_MODULES
 319
 320 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
 321 {
 322         struct static_key *key = jump_entry_key(entry);
 323         bool type = static_key_type(key);
 324         bool branch = jump_entry_branch(entry);
 325
 326         /* See the comment in linux/jump_label.h */
 327         return type ^ branch;
 328 }
 329
 330 struct static_key_mod {
 331         struct static_key_mod *next;
 332         struct jump_entry *entries;
 333         struct module *mod;
 334 };
 335
 336 static int __jump_label_mod_text_reserved(void *start, void *end)
 337 {
 338         struct module *mod;
 339
 340         preempt_disable();
 341         mod = __module_text_address((unsigned long)start);
 342         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 343         preempt_enable();
 344
 345         if (!mod)
 346                 return 0;
 347
 348
 349         return __jump_label_text_reserved(mod->jump_entries,
 350                                 mod->jump_entries + mod->num_jump_entries,
 351                                 start, end);
 352 }
 353
 354 static void __jump_label_mod_update(struct static_key *key)
 355 {
 356         struct static_key_mod *mod;
 357
 358         for (mod = key->next; mod; mod = mod->next) {
 359                 struct module *m = mod->mod;
 360
 361                 __jump_label_update(key, mod->entries,
 362                                     m->jump_entries + m->num_jump_entries);
 363         }
 364 }
 365
 366 /***
 367  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 368  * @mod: module to patch
 369  *
 370  * Allow for run-time selection of the optimal nops. Before the module
 371  * loads patch these with arch_get_jump_label_nop(), which is specified by
 372  * the arch specific jump label code.
 373  */
 374 void jump_label_apply_nops(struct module *mod)
 375 {
 376         struct jump_entry *iter_start = mod->jump_entries;
 377         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 378         struct jump_entry *iter;
 379
 380         /* if the module doesn't have jump label entries, just return */
 381         if (iter_start == iter_stop)
 382                 return;
 383
 384         for (iter = iter_start; iter < iter_stop; iter++) {
 385                 /* Only write NOPs for arch_branch_static(). */
 386                 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
 387                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 388         }
 389 }
 390
 391 static int jump_label_add_module(struct module *mod)
 392 {
 393         struct jump_entry *iter_start = mod->jump_entries;
 394         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 395         struct jump_entry *iter;
 396         struct static_key *key = NULL;
 397         struct static_key_mod *jlm;
 398
 399         /* if the module doesn't have jump label entries, just return */
 400         if (iter_start == iter_stop)
 401                 return 0;
 402
 403         jump_label_sort_entries(iter_start, iter_stop);
 404
 405         for (iter = iter_start; iter < iter_stop; iter++) {
 406                 struct static_key *iterk;
 407
 408                 iterk = jump_entry_key(iter);
 409                 if (iterk == key)
 410                         continue;
 411
 412                 key = iterk;
 413                 if (within_module(iter->key, mod)) {
 414                         /*
 415                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 416                          */
 417                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 418                         key->next = NULL;
 419                         continue;
 420                 }
 421                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 422                 if (!jlm)
 423                         return -ENOMEM;
 424                 jlm->mod = mod;
 425                 jlm->entries = iter;
 426                 jlm->next = key->next;
 427                 key->next = jlm;
 428
 429                 /* Only update if we've changed from our initial state */
 430                 if (jump_label_type(iter) != jump_label_init_type(iter))
 431                         __jump_label_update(key, iter, iter_stop);
 432         }
 433
 434         return 0;
 435 }
 436
 437 static void jump_label_del_module(struct module *mod)
 438 {
 439         struct jump_entry *iter_start = mod->jump_entries;
 440         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 441         struct jump_entry *iter;
 442         struct static_key *key = NULL;
 443         struct static_key_mod *jlm, **prev;
 444
 445         for (iter = iter_start; iter < iter_stop; iter++) {
 446                 if (jump_entry_key(iter) == key)
 447                         continue;
 448
 449                 key = jump_entry_key(iter);
 450
 451                 if (within_module(iter->key, mod))
 452                         continue;
 453
 454                 prev = &key->next;
 455                 jlm = key->next;
 456
 457                 while (jlm && jlm->mod != mod) {
 458                         prev = &jlm->next;
 459                         jlm = jlm->next;
 460                 }
 461
 462                 if (jlm) {
 463                         *prev = jlm->next;
 464                         kfree(jlm);
 465                 }
 466         }
 467 }
 468
 469 static void jump_label_invalidate_module_init(struct module *mod)
 470 {
 471         struct jump_entry *iter_start = mod->jump_entries;
 472         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 473         struct jump_entry *iter;
 474
 475         for (iter = iter_start; iter < iter_stop; iter++) {
 476                 if (within_module_init(iter->code, mod))
 477                         iter->code = 0;
 478         }
 479 }
 480
 481 static int
 482 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 483                          void *data)
 484 {
 485         struct module *mod = data;
 486         int ret = 0;
 487
 488         switch (val) {
 489         case MODULE_STATE_COMING:
 490                 jump_label_lock();
 491                 ret = jump_label_add_module(mod);
 492                 if (ret)
 493                         jump_label_del_module(mod);
 494                 jump_label_unlock();
 495                 break;
 496         case MODULE_STATE_GOING:
 497                 jump_label_lock();
 498                 jump_label_del_module(mod);
 499                 jump_label_unlock();
 500                 break;
 501         case MODULE_STATE_LIVE:
 502                 jump_label_lock();
 503                 jump_label_invalidate_module_init(mod);
 504                 jump_label_unlock();
 505                 break;
 506         }
 507
 508         return notifier_from_errno(ret);
 509 }
 510
 511 static struct notifier_block jump_label_module_nb = {
 512         .notifier_call = jump_label_module_notify,
 513         .priority = 1, /* higher than tracepoints */
 514 };
 515
 516 static __init int jump_label_init_module(void)
 517 {
 518         return register_module_notifier(&jump_label_module_nb);
 519 }
 520 early_initcall(jump_label_init_module);
 521
 522 #endif /* CONFIG_MODULES */
 523
 524 /***
 525  * jump_label_text_reserved - check if addr range is reserved
 526  * @start: start text addr
 527  * @end: end text addr
 528  *
 529  * checks if the text addr located between @start and @end
 530  * overlaps with any of the jump label patch addresses. Code
 531  * that wants to modify kernel text should first verify that
 532  * it does not overlap with any of the jump label addresses.
 533  * Caller must hold jump_label_mutex.
 534  *
 535  * returns 1 if there is an overlap, 0 otherwise
 536  */
 537 int jump_label_text_reserved(void *start, void *end)
 538 {
 539         int ret = __jump_label_text_reserved(__start___jump_table,
 540                         __stop___jump_table, start, end);
 541
 542         if (ret)
 543                 return ret;
 544
 545 #ifdef CONFIG_MODULES
 546         ret = __jump_label_mod_text_reserved(start, end);
 547 #endif
 548         return ret;
 549 }
 550
 551 static void jump_label_update(struct static_key *key)
 552 {
 553         struct jump_entry *stop = __stop___jump_table;
 554         struct jump_entry *entry = static_key_entries(key);
 555 #ifdef CONFIG_MODULES
 556         struct module *mod;
 557
 558         __jump_label_mod_update(key);
 559
 560         preempt_disable();
 561         mod = __module_address((unsigned long)key);
 562         if (mod)
 563                 stop = mod->jump_entries + mod->num_jump_entries;
 564         preempt_enable();
 565 #endif
 566         /* if there are no users, entry can be NULL */
 567         if (entry)
 568                 __jump_label_update(key, entry, stop);
 569 }
 570
 571 #ifdef CONFIG_STATIC_KEYS_SELFTEST
 572 static DEFINE_STATIC_KEY_TRUE(sk_true);
 573 static DEFINE_STATIC_KEY_FALSE(sk_false);
 574
 575 static __init int jump_label_test(void)
 576 {
 577         int i;
 578
 579         for (i = 0; i < 2; i++) {
 580                 WARN_ON(static_key_enabled(&sk_true.key) != true);
 581                 WARN_ON(static_key_enabled(&sk_false.key) != false);
 582
 583                 WARN_ON(!static_branch_likely(&sk_true));
 584                 WARN_ON(!static_branch_unlikely(&sk_true));
 585                 WARN_ON(static_branch_likely(&sk_false));
 586                 WARN_ON(static_branch_unlikely(&sk_false));
 587
 588                 static_branch_disable(&sk_true);
 589                 static_branch_enable(&sk_false);
 590
 591                 WARN_ON(static_key_enabled(&sk_true.key) == true);
 592                 WARN_ON(static_key_enabled(&sk_false.key) == false);
 593
 594                 WARN_ON(static_branch_likely(&sk_true));
 595                 WARN_ON(static_branch_unlikely(&sk_true));
 596                 WARN_ON(!static_branch_likely(&sk_false));
 597                 WARN_ON(!static_branch_unlikely(&sk_false));
 598
 599                 static_branch_enable(&sk_true);
 600                 static_branch_disable(&sk_false);
 601         }
 602
 603         return 0;
 604 }
 605 late_initcall(jump_label_test);
 606 #endif /* STATIC_KEYS_SELFTEST */
 607
 608 #endif /* HAVE_JUMP_LABEL */