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 static_key_deferred_flush(struct static_key_deferred *key)
 186 {
 187         STATIC_KEY_CHECK_USE();
 188         flush_delayed_work(&key->work);
 189 }
 190 EXPORT_SYMBOL_GPL(static_key_deferred_flush);
 191
 192 void jump_label_rate_limit(struct static_key_deferred *key,
 193                 unsigned long rl)
 194 {
 195         STATIC_KEY_CHECK_USE();
 196         key->timeout = rl;
 197         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 198 }
 199 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 200
 201 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 202 {
 203         if (entry->code <= (unsigned long)end &&
 204                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 205                 return 1;
 206
 207         return 0;
 208 }
 209
 210 static int __jump_label_text_reserved(struct jump_entry *iter_start,
 211                 struct jump_entry *iter_stop, void *start, void *end)
 212 {
 213         struct jump_entry *iter;
 214
 215         iter = iter_start;
 216         while (iter < iter_stop) {
 217                 if (addr_conflict(iter, start, end))
 218                         return 1;
 219                 iter++;
 220         }
 221
 222         return 0;
 223 }
 224
 225 /*
 226  * Update code which is definitely not currently executing.
 227  * Architectures which need heavyweight synchronization to modify
 228  * running code can override this to make the non-live update case
 229  * cheaper.
 230  */
 231 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 232                                             enum jump_label_type type)
 233 {
 234         arch_jump_label_transform(entry, type);
 235 }
 236
 237 static inline struct jump_entry *static_key_entries(struct static_key *key)
 238 {
 239         return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
 240 }
 241
 242 static inline bool static_key_type(struct static_key *key)
 243 {
 244         return (unsigned long)key->entries & JUMP_TYPE_MASK;
 245 }
 246
 247 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
 248 {
 249         return (struct static_key *)((unsigned long)entry->key & ~1UL);
 250 }
 251
 252 static bool jump_entry_branch(struct jump_entry *entry)
 253 {
 254         return (unsigned long)entry->key & 1UL;
 255 }
 256
 257 static enum jump_label_type jump_label_type(struct jump_entry *entry)
 258 {
 259         struct static_key *key = jump_entry_key(entry);
 260         bool enabled = static_key_enabled(key);
 261         bool branch = jump_entry_branch(entry);
 262
 263         /* See the comment in linux/jump_label.h */
 264         return enabled ^ branch;
 265 }
 266
 267 static void __jump_label_update(struct static_key *key,
 268                                 struct jump_entry *entry,
 269                                 struct jump_entry *stop)
 270 {
 271         for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
 272                 /*
 273                  * entry->code set to 0 invalidates module init text sections
 274                  * kernel_text_address() verifies we are not in core kernel
 275                  * init code, see jump_label_invalidate_module_init().
 276                  */
 277                 if (entry->code && kernel_text_address(entry->code))
 278                         arch_jump_label_transform(entry, jump_label_type(entry));
 279         }
 280 }
 281
 282 void __init jump_label_init(void)
 283 {
 284         struct jump_entry *iter_start = __start___jump_table;
 285         struct jump_entry *iter_stop = __stop___jump_table;
 286         struct static_key *key = NULL;
 287         struct jump_entry *iter;
 288
 289         /*
 290          * Since we are initializing the static_key.enabled field with
 291          * with the 'raw' int values (to avoid pulling in atomic.h) in
 292          * jump_label.h, let's make sure that is safe. There are only two
 293          * cases to check since we initialize to 0 or 1.
 294          */
 295         BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
 296         BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);
 297
 298         if (static_key_initialized)
 299                 return;
 300
 301         jump_label_lock();
 302         jump_label_sort_entries(iter_start, iter_stop);
 303
 304         for (iter = iter_start; iter < iter_stop; iter++) {
 305                 struct static_key *iterk;
 306
 307                 /* rewrite NOPs */
 308                 if (jump_label_type(iter) == JUMP_LABEL_NOP)
 309                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 310
 311                 iterk = jump_entry_key(iter);
 312                 if (iterk == key)
 313                         continue;
 314
 315                 key = iterk;
 316                 /*
 317                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 318                  */
 319                 *((unsigned long *)&key->entries) += (unsigned long)iter;
 320 #ifdef CONFIG_MODULES
 321                 key->next = NULL;
 322 #endif
 323         }
 324         static_key_initialized = true;
 325         jump_label_unlock();
 326 }
 327
 328 #ifdef CONFIG_MODULES
 329
 330 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
 331 {
 332         struct static_key *key = jump_entry_key(entry);
 333         bool type = static_key_type(key);
 334         bool branch = jump_entry_branch(entry);
 335
 336         /* See the comment in linux/jump_label.h */
 337         return type ^ branch;
 338 }
 339
 340 struct static_key_mod {
 341         struct static_key_mod *next;
 342         struct jump_entry *entries;
 343         struct module *mod;
 344 };
 345
 346 static int __jump_label_mod_text_reserved(void *start, void *end)
 347 {
 348         struct module *mod;
 349
 350         preempt_disable();
 351         mod = __module_text_address((unsigned long)start);
 352         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 353         preempt_enable();
 354
 355         if (!mod)
 356                 return 0;
 357
 358
 359         return __jump_label_text_reserved(mod->jump_entries,
 360                                 mod->jump_entries + mod->num_jump_entries,
 361                                 start, end);
 362 }
 363
 364 static void __jump_label_mod_update(struct static_key *key)
 365 {
 366         struct static_key_mod *mod;
 367
 368         for (mod = key->next; mod; mod = mod->next) {
 369                 struct module *m = mod->mod;
 370
 371                 __jump_label_update(key, mod->entries,
 372                                     m->jump_entries + m->num_jump_entries);
 373         }
 374 }
 375
 376 /***
 377  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 378  * @mod: module to patch
 379  *
 380  * Allow for run-time selection of the optimal nops. Before the module
 381  * loads patch these with arch_get_jump_label_nop(), which is specified by
 382  * the arch specific jump label code.
 383  */
 384 void jump_label_apply_nops(struct module *mod)
 385 {
 386         struct jump_entry *iter_start = mod->jump_entries;
 387         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 388         struct jump_entry *iter;
 389
 390         /* if the module doesn't have jump label entries, just return */
 391         if (iter_start == iter_stop)
 392                 return;
 393
 394         for (iter = iter_start; iter < iter_stop; iter++) {
 395                 /* Only write NOPs for arch_branch_static(). */
 396                 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
 397                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 398         }
 399 }
 400
 401 static int jump_label_add_module(struct module *mod)
 402 {
 403         struct jump_entry *iter_start = mod->jump_entries;
 404         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 405         struct jump_entry *iter;
 406         struct static_key *key = NULL;
 407         struct static_key_mod *jlm;
 408
 409         /* if the module doesn't have jump label entries, just return */
 410         if (iter_start == iter_stop)
 411                 return 0;
 412
 413         jump_label_sort_entries(iter_start, iter_stop);
 414
 415         for (iter = iter_start; iter < iter_stop; iter++) {
 416                 struct static_key *iterk;
 417
 418                 iterk = jump_entry_key(iter);
 419                 if (iterk == key)
 420                         continue;
 421
 422                 key = iterk;
 423                 if (within_module(iter->key, mod)) {
 424                         /*
 425                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 426                          */
 427                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 428                         key->next = NULL;
 429                         continue;
 430                 }
 431                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 432                 if (!jlm)
 433                         return -ENOMEM;
 434                 jlm->mod = mod;
 435                 jlm->entries = iter;
 436                 jlm->next = key->next;
 437                 key->next = jlm;
 438
 439                 /* Only update if we've changed from our initial state */
 440                 if (jump_label_type(iter) != jump_label_init_type(iter))
 441                         __jump_label_update(key, iter, iter_stop);
 442         }
 443
 444         return 0;
 445 }
 446
 447 static void jump_label_del_module(struct module *mod)
 448 {
 449         struct jump_entry *iter_start = mod->jump_entries;
 450         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 451         struct jump_entry *iter;
 452         struct static_key *key = NULL;
 453         struct static_key_mod *jlm, **prev;
 454
 455         for (iter = iter_start; iter < iter_stop; iter++) {
 456                 if (jump_entry_key(iter) == key)
 457                         continue;
 458
 459                 key = jump_entry_key(iter);
 460
 461                 if (within_module(iter->key, mod))
 462                         continue;
 463
 464                 prev = &key->next;
 465                 jlm = key->next;
 466
 467                 while (jlm && jlm->mod != mod) {
 468                         prev = &jlm->next;
 469                         jlm = jlm->next;
 470                 }
 471
 472                 if (jlm) {
 473                         *prev = jlm->next;
 474                         kfree(jlm);
 475                 }
 476         }
 477 }
 478
 479 static void jump_label_invalidate_module_init(struct module *mod)
 480 {
 481         struct jump_entry *iter_start = mod->jump_entries;
 482         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 483         struct jump_entry *iter;
 484
 485         for (iter = iter_start; iter < iter_stop; iter++) {
 486                 if (within_module_init(iter->code, mod))
 487                         iter->code = 0;
 488         }
 489 }
 490
 491 static int
 492 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 493                          void *data)
 494 {
 495         struct module *mod = data;
 496         int ret = 0;
 497
 498         switch (val) {
 499         case MODULE_STATE_COMING:
 500                 jump_label_lock();
 501                 ret = jump_label_add_module(mod);
 502                 if (ret)
 503                         jump_label_del_module(mod);
 504                 jump_label_unlock();
 505                 break;
 506         case MODULE_STATE_GOING:
 507                 jump_label_lock();
 508                 jump_label_del_module(mod);
 509                 jump_label_unlock();
 510                 break;
 511         case MODULE_STATE_LIVE:
 512                 jump_label_lock();
 513                 jump_label_invalidate_module_init(mod);
 514                 jump_label_unlock();
 515                 break;
 516         }
 517
 518         return notifier_from_errno(ret);
 519 }
 520
 521 static struct notifier_block jump_label_module_nb = {
 522         .notifier_call = jump_label_module_notify,
 523         .priority = 1, /* higher than tracepoints */
 524 };
 525
 526 static __init int jump_label_init_module(void)
 527 {
 528         return register_module_notifier(&jump_label_module_nb);
 529 }
 530 early_initcall(jump_label_init_module);
 531
 532 #endif /* CONFIG_MODULES */
 533
 534 /***
 535  * jump_label_text_reserved - check if addr range is reserved
 536  * @start: start text addr
 537  * @end: end text addr
 538  *
 539  * checks if the text addr located between @start and @end
 540  * overlaps with any of the jump label patch addresses. Code
 541  * that wants to modify kernel text should first verify that
 542  * it does not overlap with any of the jump label addresses.
 543  * Caller must hold jump_label_mutex.
 544  *
 545  * returns 1 if there is an overlap, 0 otherwise
 546  */
 547 int jump_label_text_reserved(void *start, void *end)
 548 {
 549         int ret = __jump_label_text_reserved(__start___jump_table,
 550                         __stop___jump_table, start, end);
 551
 552         if (ret)
 553                 return ret;
 554
 555 #ifdef CONFIG_MODULES
 556         ret = __jump_label_mod_text_reserved(start, end);
 557 #endif
 558         return ret;
 559 }
 560
 561 static void jump_label_update(struct static_key *key)
 562 {
 563         struct jump_entry *stop = __stop___jump_table;
 564         struct jump_entry *entry = static_key_entries(key);
 565 #ifdef CONFIG_MODULES
 566         struct module *mod;
 567
 568         __jump_label_mod_update(key);
 569
 570         preempt_disable();
 571         mod = __module_address((unsigned long)key);
 572         if (mod)
 573                 stop = mod->jump_entries + mod->num_jump_entries;
 574         preempt_enable();
 575 #endif
 576         /* if there are no users, entry can be NULL */
 577         if (entry)
 578                 __jump_label_update(key, entry, stop);
 579 }
 580
 581 #ifdef CONFIG_STATIC_KEYS_SELFTEST
 582 static DEFINE_STATIC_KEY_TRUE(sk_true);
 583 static DEFINE_STATIC_KEY_FALSE(sk_false);
 584
 585 static __init int jump_label_test(void)
 586 {
 587         int i;
 588
 589         for (i = 0; i < 2; i++) {
 590                 WARN_ON(static_key_enabled(&sk_true.key) != true);
 591                 WARN_ON(static_key_enabled(&sk_false.key) != false);
 592
 593                 WARN_ON(!static_branch_likely(&sk_true));
 594                 WARN_ON(!static_branch_unlikely(&sk_true));
 595                 WARN_ON(static_branch_likely(&sk_false));
 596                 WARN_ON(static_branch_unlikely(&sk_false));
 597
 598                 static_branch_disable(&sk_true);
 599                 static_branch_enable(&sk_false);
 600
 601                 WARN_ON(static_key_enabled(&sk_true.key) == true);
 602                 WARN_ON(static_key_enabled(&sk_false.key) == false);
 603
 604                 WARN_ON(static_branch_likely(&sk_true));
 605                 WARN_ON(static_branch_unlikely(&sk_true));
 606                 WARN_ON(!static_branch_likely(&sk_false));
 607                 WARN_ON(!static_branch_unlikely(&sk_false));
 608
 609                 static_branch_enable(&sk_true);
 610                 static_branch_disable(&sk_false);
 611         }
 612
 613         return 0;
 614 }
 615 late_initcall(jump_label_test);
 616 #endif /* STATIC_KEYS_SELFTEST */
 617
 618 #endif /* HAVE_JUMP_LABEL */