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