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 jump_label_rate_limit(struct static_key_deferred *key,
 120                 unsigned long rl)
 121 {
 122         STATIC_KEY_CHECK_USE();
 123         key->timeout = rl;
 124         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 125 }
 126 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 127
 128 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 129 {
 130         if (entry->code <= (unsigned long)end &&
 131                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 132                 return 1;
 133
 134         return 0;
 135 }
 136
 137 static int __jump_label_text_reserved(struct jump_entry *iter_start,
 138                 struct jump_entry *iter_stop, void *start, void *end)
 139 {
 140         struct jump_entry *iter;
 141
 142         iter = iter_start;
 143         while (iter < iter_stop) {
 144                 if (addr_conflict(iter, start, end))
 145                         return 1;
 146                 iter++;
 147         }
 148
 149         return 0;
 150 }
 151
 152 /*
 153  * Update code which is definitely not currently executing.
 154  * Architectures which need heavyweight synchronization to modify
 155  * running code can override this to make the non-live update case
 156  * cheaper.
 157  */
 158 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 159                                             enum jump_label_type type)
 160 {
 161         arch_jump_label_transform(entry, type);
 162 }
 163
 164 static void __jump_label_update(struct static_key *key,
 165                                 struct jump_entry *entry,
 166                                 struct jump_entry *stop, int enable)
 167 {
 168         for (; (entry < stop) &&
 169               (entry->key == (jump_label_t)(unsigned long)key);
 170               entry++) {
 171                 /*
 172                  * entry->code set to 0 invalidates module init text sections
 173                  * kernel_text_address() verifies we are not in core kernel
 174                  * init code, see jump_label_invalidate_module_init().
 175                  */
 176                 if (entry->code && kernel_text_address(entry->code))
 177                         arch_jump_label_transform(entry, enable);
 178         }
 179 }
 180
 181 static enum jump_label_type jump_label_type(struct static_key *key)
 182 {
 183         bool true_branch = jump_label_get_branch_default(key);
 184         bool state = static_key_enabled(key);
 185
 186         if ((!true_branch && state) || (true_branch && !state))
 187                 return JUMP_LABEL_ENABLE;
 188
 189         return JUMP_LABEL_DISABLE;
 190 }
 191
 192 void __init jump_label_init(void)
 193 {
 194         struct jump_entry *iter_start = __start___jump_table;
 195         struct jump_entry *iter_stop = __stop___jump_table;
 196         struct static_key *key = NULL;
 197         struct jump_entry *iter;
 198
 199         jump_label_lock();
 200         jump_label_sort_entries(iter_start, iter_stop);
 201
 202         for (iter = iter_start; iter < iter_stop; iter++) {
 203                 struct static_key *iterk;
 204
 205                 iterk = (struct static_key *)(unsigned long)iter->key;
 206                 arch_jump_label_transform_static(iter, jump_label_type(iterk));
 207                 if (iterk == key)
 208                         continue;
 209
 210                 key = iterk;
 211                 /*
 212                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 213                  */
 214                 *((unsigned long *)&key->entries) += (unsigned long)iter;
 215 #ifdef CONFIG_MODULES
 216                 key->next = NULL;
 217 #endif
 218         }
 219         static_key_initialized = true;
 220         jump_label_unlock();
 221 }
 222
 223 #ifdef CONFIG_MODULES
 224
 225 struct static_key_mod {
 226         struct static_key_mod *next;
 227         struct jump_entry *entries;
 228         struct module *mod;
 229 };
 230
 231 static int __jump_label_mod_text_reserved(void *start, void *end)
 232 {
 233         struct module *mod;
 234
 235         mod = __module_text_address((unsigned long)start);
 236         if (!mod)
 237                 return 0;
 238
 239         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 240
 241         return __jump_label_text_reserved(mod->jump_entries,
 242                                 mod->jump_entries + mod->num_jump_entries,
 243                                 start, end);
 244 }
 245
 246 static void __jump_label_mod_update(struct static_key *key, int enable)
 247 {
 248         struct static_key_mod *mod = key->next;
 249
 250         while (mod) {
 251                 struct module *m = mod->mod;
 252
 253                 __jump_label_update(key, mod->entries,
 254                                     m->jump_entries + m->num_jump_entries,
 255                                     enable);
 256                 mod = mod->next;
 257         }
 258 }
 259
 260 /***
 261  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 262  * @mod: module to patch
 263  *
 264  * Allow for run-time selection of the optimal nops. Before the module
 265  * loads patch these with arch_get_jump_label_nop(), which is specified by
 266  * the arch specific jump label code.
 267  */
 268 void jump_label_apply_nops(struct module *mod)
 269 {
 270         struct jump_entry *iter_start = mod->jump_entries;
 271         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 272         struct jump_entry *iter;
 273
 274         /* if the module doesn't have jump label entries, just return */
 275         if (iter_start == iter_stop)
 276                 return;
 277
 278         for (iter = iter_start; iter < iter_stop; iter++) {
 279                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 280         }
 281 }
 282
 283 static int jump_label_add_module(struct module *mod)
 284 {
 285         struct jump_entry *iter_start = mod->jump_entries;
 286         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 287         struct jump_entry *iter;
 288         struct static_key *key = NULL;
 289         struct static_key_mod *jlm;
 290
 291         /* if the module doesn't have jump label entries, just return */
 292         if (iter_start == iter_stop)
 293                 return 0;
 294
 295         jump_label_sort_entries(iter_start, iter_stop);
 296
 297         for (iter = iter_start; iter < iter_stop; iter++) {
 298                 struct static_key *iterk;
 299
 300                 iterk = (struct static_key *)(unsigned long)iter->key;
 301                 if (iterk == key)
 302                         continue;
 303
 304                 key = iterk;
 305                 if (within_module(iter->key, mod)) {
 306                         /*
 307                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 308                          */
 309                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 310                         key->next = NULL;
 311                         continue;
 312                 }
 313                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 314                 if (!jlm)
 315                         return -ENOMEM;
 316                 jlm->mod = mod;
 317                 jlm->entries = iter;
 318                 jlm->next = key->next;
 319                 key->next = jlm;
 320
 321                 if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 322                         __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 323         }
 324
 325         return 0;
 326 }
 327
 328 static void jump_label_del_module(struct module *mod)
 329 {
 330         struct jump_entry *iter_start = mod->jump_entries;
 331         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 332         struct jump_entry *iter;
 333         struct static_key *key = NULL;
 334         struct static_key_mod *jlm, **prev;
 335
 336         for (iter = iter_start; iter < iter_stop; iter++) {
 337                 if (iter->key == (jump_label_t)(unsigned long)key)
 338                         continue;
 339
 340                 key = (struct static_key *)(unsigned long)iter->key;
 341
 342                 if (within_module(iter->key, mod))
 343                         continue;
 344
 345                 prev = &key->next;
 346                 jlm = key->next;
 347
 348                 while (jlm && jlm->mod != mod) {
 349                         prev = &jlm->next;
 350                         jlm = jlm->next;
 351                 }
 352
 353                 if (jlm) {
 354                         *prev = jlm->next;
 355                         kfree(jlm);
 356                 }
 357         }
 358 }
 359
 360 static void jump_label_invalidate_module_init(struct module *mod)
 361 {
 362         struct jump_entry *iter_start = mod->jump_entries;
 363         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 364         struct jump_entry *iter;
 365
 366         for (iter = iter_start; iter < iter_stop; iter++) {
 367                 if (within_module_init(iter->code, mod))
 368                         iter->code = 0;
 369         }
 370 }
 371
 372 static int
 373 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 374                          void *data)
 375 {
 376         struct module *mod = data;
 377         int ret = 0;
 378
 379         switch (val) {
 380         case MODULE_STATE_COMING:
 381                 jump_label_lock();
 382                 ret = jump_label_add_module(mod);
 383                 if (ret)
 384                         jump_label_del_module(mod);
 385                 jump_label_unlock();
 386                 break;
 387         case MODULE_STATE_GOING:
 388                 jump_label_lock();
 389                 jump_label_del_module(mod);
 390                 jump_label_unlock();
 391                 break;
 392         case MODULE_STATE_LIVE:
 393                 jump_label_lock();
 394                 jump_label_invalidate_module_init(mod);
 395                 jump_label_unlock();
 396                 break;
 397         }
 398
 399         return notifier_from_errno(ret);
 400 }
 401
 402 struct notifier_block jump_label_module_nb = {
 403         .notifier_call = jump_label_module_notify,
 404         .priority = 1, /* higher than tracepoints */
 405 };
 406
 407 static __init int jump_label_init_module(void)
 408 {
 409         return register_module_notifier(&jump_label_module_nb);
 410 }
 411 early_initcall(jump_label_init_module);
 412
 413 #endif /* CONFIG_MODULES */
 414
 415 /***
 416  * jump_label_text_reserved - check if addr range is reserved
 417  * @start: start text addr
 418  * @end: end text addr
 419  *
 420  * checks if the text addr located between @start and @end
 421  * overlaps with any of the jump label patch addresses. Code
 422  * that wants to modify kernel text should first verify that
 423  * it does not overlap with any of the jump label addresses.
 424  * Caller must hold jump_label_mutex.
 425  *
 426  * returns 1 if there is an overlap, 0 otherwise
 427  */
 428 int jump_label_text_reserved(void *start, void *end)
 429 {
 430         int ret = __jump_label_text_reserved(__start___jump_table,
 431                         __stop___jump_table, start, end);
 432
 433         if (ret)
 434                 return ret;
 435
 436 #ifdef CONFIG_MODULES
 437         ret = __jump_label_mod_text_reserved(start, end);
 438 #endif
 439         return ret;
 440 }
 441
 442 static void jump_label_update(struct static_key *key, int enable)
 443 {
 444         struct jump_entry *stop = __stop___jump_table;
 445         struct jump_entry *entry = jump_label_get_entries(key);
 446 #ifdef CONFIG_MODULES
 447         struct module *mod;
 448
 449         __jump_label_mod_update(key, enable);
 450
 451         preempt_disable();
 452         mod = __module_address((unsigned long)key);
 453         if (mod)
 454                 stop = mod->jump_entries + mod->num_jump_entries;
 455         preempt_enable();
 456 #endif
 457         /* if there are no users, entry can be NULL */
 458         if (entry)
 459                 __jump_label_update(key, entry, stop, enable);
 460 }
 461
 462 #endif