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