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 jump_label_rate_limit(struct static_key_deferred *key,
 142                 unsigned long rl)
 143 {
 144         STATIC_KEY_CHECK_USE();
 145         key->timeout = rl;
 146         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 147 }
 148 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 149
 150 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 151 {
 152         if (entry->code <= (unsigned long)end &&
 153                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 154                 return 1;
 155
 156         return 0;
 157 }
 158
 159 static int __jump_label_text_reserved(struct jump_entry *iter_start,
 160                 struct jump_entry *iter_stop, void *start, void *end)
 161 {
 162         struct jump_entry *iter;
 163
 164         iter = iter_start;
 165         while (iter < iter_stop) {
 166                 if (addr_conflict(iter, start, end))
 167                         return 1;
 168                 iter++;
 169         }
 170
 171         return 0;
 172 }
 173
 174 /*
 175  * Update code which is definitely not currently executing.
 176  * Architectures which need heavyweight synchronization to modify
 177  * running code can override this to make the non-live update case
 178  * cheaper.
 179  */
 180 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 181                                             enum jump_label_type type)
 182 {
 183         arch_jump_label_transform(entry, type);
 184 }
 185
 186 static inline struct jump_entry *static_key_entries(struct static_key *key)
 187 {
 188         return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
 189 }
 190
 191 static inline bool static_key_type(struct static_key *key)
 192 {
 193         return (unsigned long)key->entries & JUMP_TYPE_MASK;
 194 }
 195
 196 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
 197 {
 198         return (struct static_key *)((unsigned long)entry->key & ~1UL);
 199 }
 200
 201 static bool jump_entry_branch(struct jump_entry *entry)
 202 {
 203         return (unsigned long)entry->key & 1UL;
 204 }
 205
 206 static enum jump_label_type jump_label_type(struct jump_entry *entry)
 207 {
 208         struct static_key *key = jump_entry_key(entry);
 209         bool enabled = static_key_enabled(key);
 210         bool branch = jump_entry_branch(entry);
 211
 212         /* See the comment in linux/jump_label.h */
 213         return enabled ^ branch;
 214 }
 215
 216 static void __jump_label_update(struct static_key *key,
 217                                 struct jump_entry *entry,
 218                                 struct jump_entry *stop)
 219 {
 220         for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
 221                 /*
 222                  * entry->code set to 0 invalidates module init text sections
 223                  * kernel_text_address() verifies we are not in core kernel
 224                  * init code, see jump_label_invalidate_module_init().
 225                  */
 226                 if (entry->code && kernel_text_address(entry->code))
 227                         arch_jump_label_transform(entry, jump_label_type(entry));
 228         }
 229 }
 230
 231 void __init jump_label_init(void)
 232 {
 233         struct jump_entry *iter_start = __start___jump_table;
 234         struct jump_entry *iter_stop = __stop___jump_table;
 235         struct static_key *key = NULL;
 236         struct jump_entry *iter;
 237
 238         if (static_key_initialized)
 239                 return;
 240
 241         jump_label_lock();
 242         jump_label_sort_entries(iter_start, iter_stop);
 243
 244         for (iter = iter_start; iter < iter_stop; iter++) {
 245                 struct static_key *iterk;
 246
 247                 /* rewrite NOPs */
 248                 if (jump_label_type(iter) == JUMP_LABEL_NOP)
 249                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 250
 251                 iterk = jump_entry_key(iter);
 252                 if (iterk == key)
 253                         continue;
 254
 255                 key = iterk;
 256                 /*
 257                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 258                  */
 259                 *((unsigned long *)&key->entries) += (unsigned long)iter;
 260 #ifdef CONFIG_MODULES
 261                 key->next = NULL;
 262 #endif
 263         }
 264         static_key_initialized = true;
 265         jump_label_unlock();
 266 }
 267
 268 #ifdef CONFIG_MODULES
 269
 270 static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
 271 {
 272         struct static_key *key = jump_entry_key(entry);
 273         bool type = static_key_type(key);
 274         bool branch = jump_entry_branch(entry);
 275
 276         /* See the comment in linux/jump_label.h */
 277         return type ^ branch;
 278 }
 279
 280 struct static_key_mod {
 281         struct static_key_mod *next;
 282         struct jump_entry *entries;
 283         struct module *mod;
 284 };
 285
 286 static int __jump_label_mod_text_reserved(void *start, void *end)
 287 {
 288         struct module *mod;
 289
 290         mod = __module_text_address((unsigned long)start);
 291         if (!mod)
 292                 return 0;
 293
 294         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 295
 296         return __jump_label_text_reserved(mod->jump_entries,
 297                                 mod->jump_entries + mod->num_jump_entries,
 298                                 start, end);
 299 }
 300
 301 static void __jump_label_mod_update(struct static_key *key)
 302 {
 303         struct static_key_mod *mod;
 304
 305         for (mod = key->next; mod; mod = mod->next) {
 306                 struct module *m = mod->mod;
 307
 308                 __jump_label_update(key, mod->entries,
 309                                     m->jump_entries + m->num_jump_entries);
 310         }
 311 }
 312
 313 /***
 314  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 315  * @mod: module to patch
 316  *
 317  * Allow for run-time selection of the optimal nops. Before the module
 318  * loads patch these with arch_get_jump_label_nop(), which is specified by
 319  * the arch specific jump label code.
 320  */
 321 void jump_label_apply_nops(struct module *mod)
 322 {
 323         struct jump_entry *iter_start = mod->jump_entries;
 324         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 325         struct jump_entry *iter;
 326
 327         /* if the module doesn't have jump label entries, just return */
 328         if (iter_start == iter_stop)
 329                 return;
 330
 331         for (iter = iter_start; iter < iter_stop; iter++) {
 332                 /* Only write NOPs for arch_branch_static(). */
 333                 if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
 334                         arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 335         }
 336 }
 337
 338 static int jump_label_add_module(struct module *mod)
 339 {
 340         struct jump_entry *iter_start = mod->jump_entries;
 341         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 342         struct jump_entry *iter;
 343         struct static_key *key = NULL;
 344         struct static_key_mod *jlm;
 345
 346         /* if the module doesn't have jump label entries, just return */
 347         if (iter_start == iter_stop)
 348                 return 0;
 349
 350         jump_label_sort_entries(iter_start, iter_stop);
 351
 352         for (iter = iter_start; iter < iter_stop; iter++) {
 353                 struct static_key *iterk;
 354
 355                 iterk = jump_entry_key(iter);
 356                 if (iterk == key)
 357                         continue;
 358
 359                 key = iterk;
 360                 if (within_module(iter->key, mod)) {
 361                         /*
 362                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 363                          */
 364                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 365                         key->next = NULL;
 366                         continue;
 367                 }
 368                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 369                 if (!jlm)
 370                         return -ENOMEM;
 371                 jlm->mod = mod;
 372                 jlm->entries = iter;
 373                 jlm->next = key->next;
 374                 key->next = jlm;
 375
 376                 /* Only update if we've changed from our initial state */
 377                 if (jump_label_type(iter) != jump_label_init_type(iter))
 378                         __jump_label_update(key, iter, iter_stop);
 379         }
 380
 381         return 0;
 382 }
 383
 384 static void jump_label_del_module(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         struct static_key *key = NULL;
 390         struct static_key_mod *jlm, **prev;
 391
 392         for (iter = iter_start; iter < iter_stop; iter++) {
 393                 if (jump_entry_key(iter) == key)
 394                         continue;
 395
 396                 key = jump_entry_key(iter);
 397
 398                 if (within_module(iter->key, mod))
 399                         continue;
 400
 401                 prev = &key->next;
 402                 jlm = key->next;
 403
 404                 while (jlm && jlm->mod != mod) {
 405                         prev = &jlm->next;
 406                         jlm = jlm->next;
 407                 }
 408
 409                 if (jlm) {
 410                         *prev = jlm->next;
 411                         kfree(jlm);
 412                 }
 413         }
 414 }
 415
 416 static void jump_label_invalidate_module_init(struct module *mod)
 417 {
 418         struct jump_entry *iter_start = mod->jump_entries;
 419         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 420         struct jump_entry *iter;
 421
 422         for (iter = iter_start; iter < iter_stop; iter++) {
 423                 if (within_module_init(iter->code, mod))
 424                         iter->code = 0;
 425         }
 426 }
 427
 428 static int
 429 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 430                          void *data)
 431 {
 432         struct module *mod = data;
 433         int ret = 0;
 434
 435         switch (val) {
 436         case MODULE_STATE_COMING:
 437                 jump_label_lock();
 438                 ret = jump_label_add_module(mod);
 439                 if (ret)
 440                         jump_label_del_module(mod);
 441                 jump_label_unlock();
 442                 break;
 443         case MODULE_STATE_GOING:
 444                 jump_label_lock();
 445                 jump_label_del_module(mod);
 446                 jump_label_unlock();
 447                 break;
 448         case MODULE_STATE_LIVE:
 449                 jump_label_lock();
 450                 jump_label_invalidate_module_init(mod);
 451                 jump_label_unlock();
 452                 break;
 453         }
 454
 455         return notifier_from_errno(ret);
 456 }
 457
 458 static struct notifier_block jump_label_module_nb = {
 459         .notifier_call = jump_label_module_notify,
 460         .priority = 1, /* higher than tracepoints */
 461 };
 462
 463 static __init int jump_label_init_module(void)
 464 {
 465         return register_module_notifier(&jump_label_module_nb);
 466 }
 467 early_initcall(jump_label_init_module);
 468
 469 #endif /* CONFIG_MODULES */
 470
 471 /***
 472  * jump_label_text_reserved - check if addr range is reserved
 473  * @start: start text addr
 474  * @end: end text addr
 475  *
 476  * checks if the text addr located between @start and @end
 477  * overlaps with any of the jump label patch addresses. Code
 478  * that wants to modify kernel text should first verify that
 479  * it does not overlap with any of the jump label addresses.
 480  * Caller must hold jump_label_mutex.
 481  *
 482  * returns 1 if there is an overlap, 0 otherwise
 483  */
 484 int jump_label_text_reserved(void *start, void *end)
 485 {
 486         int ret = __jump_label_text_reserved(__start___jump_table,
 487                         __stop___jump_table, start, end);
 488
 489         if (ret)
 490                 return ret;
 491
 492 #ifdef CONFIG_MODULES
 493         ret = __jump_label_mod_text_reserved(start, end);
 494 #endif
 495         return ret;
 496 }
 497
 498 static void jump_label_update(struct static_key *key)
 499 {
 500         struct jump_entry *stop = __stop___jump_table;
 501         struct jump_entry *entry = static_key_entries(key);
 502 #ifdef CONFIG_MODULES
 503         struct module *mod;
 504
 505         __jump_label_mod_update(key);
 506
 507         preempt_disable();
 508         mod = __module_address((unsigned long)key);
 509         if (mod)
 510                 stop = mod->jump_entries + mod->num_jump_entries;
 511         preempt_enable();
 512 #endif
 513         /* if there are no users, entry can be NULL */
 514         if (entry)
 515                 __jump_label_update(key, entry, stop);
 516 }
 517
 518 #ifdef CONFIG_STATIC_KEYS_SELFTEST
 519 static DEFINE_STATIC_KEY_TRUE(sk_true);
 520 static DEFINE_STATIC_KEY_FALSE(sk_false);
 521
 522 static __init int jump_label_test(void)
 523 {
 524         int i;
 525
 526         for (i = 0; i < 2; i++) {
 527                 WARN_ON(static_key_enabled(&sk_true.key) != true);
 528                 WARN_ON(static_key_enabled(&sk_false.key) != false);
 529
 530                 WARN_ON(!static_branch_likely(&sk_true));
 531                 WARN_ON(!static_branch_unlikely(&sk_true));
 532                 WARN_ON(static_branch_likely(&sk_false));
 533                 WARN_ON(static_branch_unlikely(&sk_false));
 534
 535                 static_branch_disable(&sk_true);
 536                 static_branch_enable(&sk_false);
 537
 538                 WARN_ON(static_key_enabled(&sk_true.key) == true);
 539                 WARN_ON(static_key_enabled(&sk_false.key) == false);
 540
 541                 WARN_ON(static_branch_likely(&sk_true));
 542                 WARN_ON(static_branch_unlikely(&sk_true));
 543                 WARN_ON(!static_branch_likely(&sk_false));
 544                 WARN_ON(!static_branch_unlikely(&sk_false));
 545
 546                 static_branch_enable(&sk_true);
 547                 static_branch_disable(&sk_false);
 548         }
 549
 550         return 0;
 551 }
 552 late_initcall(jump_label_test);
 553 #endif /* STATIC_KEYS_SELFTEST */
 554
 555 #endif /* HAVE_JUMP_LABEL */