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