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
  17 #ifdef HAVE_JUMP_LABEL
  18
  19 /* mutex to protect coming/going of the the jump_label table */
  20 static DEFINE_MUTEX(jump_label_mutex);
  21
  22 void jump_label_lock(void)
  23 {
  24         mutex_lock(&jump_label_mutex);
  25 }
  26
  27 void jump_label_unlock(void)
  28 {
  29         mutex_unlock(&jump_label_mutex);
  30 }
  31
  32 bool static_key_enabled(struct static_key *key)
  33 {
  34         return (atomic_read(&key->enabled) > 0);
  35 }
  36 EXPORT_SYMBOL_GPL(static_key_enabled);
  37
  38 static int jump_label_cmp(const void *a, const void *b)
  39 {
  40         const struct jump_entry *jea = a;
  41         const struct jump_entry *jeb = b;
  42
  43         if (jea->key < jeb->key)
  44                 return -1;
  45
  46         if (jea->key > jeb->key)
  47                 return 1;
  48
  49         return 0;
  50 }
  51
  52 static void
  53 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
  54 {
  55         unsigned long size;
  56
  57         size = (((unsigned long)stop - (unsigned long)start)
  58                                         / sizeof(struct jump_entry));
  59         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  60 }
  61
  62 static void jump_label_update(struct static_key *key, int enable);
  63
  64 void static_key_slow_inc(struct static_key *key)
  65 {
  66         if (atomic_inc_not_zero(&key->enabled))
  67                 return;
  68
  69         jump_label_lock();
  70         if (atomic_read(&key->enabled) == 0) {
  71                 if (!jump_label_get_branch_default(key))
  72                         jump_label_update(key, JUMP_LABEL_ENABLE);
  73                 else
  74                         jump_label_update(key, JUMP_LABEL_DISABLE);
  75         }
  76         atomic_inc(&key->enabled);
  77         jump_label_unlock();
  78 }
  79 EXPORT_SYMBOL_GPL(static_key_slow_inc);
  80
  81 static void __static_key_slow_dec(struct static_key *key,
  82                 unsigned long rate_limit, struct delayed_work *work)
  83 {
  84         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
  85                 WARN(atomic_read(&key->enabled) < 0,
  86                      "jump label: negative count!\n");
  87                 return;
  88         }
  89
  90         if (rate_limit) {
  91                 atomic_inc(&key->enabled);
  92                 schedule_delayed_work(work, rate_limit);
  93         } else {
  94                 if (!jump_label_get_branch_default(key))
  95                         jump_label_update(key, JUMP_LABEL_DISABLE);
  96                 else
  97                         jump_label_update(key, JUMP_LABEL_ENABLE);
  98         }
  99         jump_label_unlock();
 100 }
 101
 102 static void jump_label_update_timeout(struct work_struct *work)
 103 {
 104         struct static_key_deferred *key =
 105                 container_of(work, struct static_key_deferred, work.work);
 106         __static_key_slow_dec(&key->key, 0, NULL);
 107 }
 108
 109 void static_key_slow_dec(struct static_key *key)
 110 {
 111         __static_key_slow_dec(key, 0, NULL);
 112 }
 113 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 114
 115 void static_key_slow_dec_deferred(struct static_key_deferred *key)
 116 {
 117         __static_key_slow_dec(&key->key, key->timeout, &key->work);
 118 }
 119 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 120
 121 void jump_label_rate_limit(struct static_key_deferred *key,
 122                 unsigned long rl)
 123 {
 124         key->timeout = rl;
 125         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 126 }
 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         jump_label_unlock();
 220 }
 221
 222 #ifdef CONFIG_MODULES
 223
 224 struct static_key_mod {
 225         struct static_key_mod *next;
 226         struct jump_entry *entries;
 227         struct module *mod;
 228 };
 229
 230 static int __jump_label_mod_text_reserved(void *start, void *end)
 231 {
 232         struct module *mod;
 233
 234         mod = __module_text_address((unsigned long)start);
 235         if (!mod)
 236                 return 0;
 237
 238         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 239
 240         return __jump_label_text_reserved(mod->jump_entries,
 241                                 mod->jump_entries + mod->num_jump_entries,
 242                                 start, end);
 243 }
 244
 245 static void __jump_label_mod_update(struct static_key *key, int enable)
 246 {
 247         struct static_key_mod *mod = key->next;
 248
 249         while (mod) {
 250                 struct module *m = mod->mod;
 251
 252                 __jump_label_update(key, mod->entries,
 253                                     m->jump_entries + m->num_jump_entries,
 254                                     enable);
 255                 mod = mod->next;
 256         }
 257 }
 258
 259 /***
 260  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 261  * @mod: module to patch
 262  *
 263  * Allow for run-time selection of the optimal nops. Before the module
 264  * loads patch these with arch_get_jump_label_nop(), which is specified by
 265  * the arch specific jump label code.
 266  */
 267 void jump_label_apply_nops(struct module *mod)
 268 {
 269         struct jump_entry *iter_start = mod->jump_entries;
 270         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 271         struct jump_entry *iter;
 272
 273         /* if the module doesn't have jump label entries, just return */
 274         if (iter_start == iter_stop)
 275                 return;
 276
 277         for (iter = iter_start; iter < iter_stop; iter++) {
 278                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 279         }
 280 }
 281
 282 static int jump_label_add_module(struct module *mod)
 283 {
 284         struct jump_entry *iter_start = mod->jump_entries;
 285         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 286         struct jump_entry *iter;
 287         struct static_key *key = NULL;
 288         struct static_key_mod *jlm;
 289
 290         /* if the module doesn't have jump label entries, just return */
 291         if (iter_start == iter_stop)
 292                 return 0;
 293
 294         jump_label_sort_entries(iter_start, iter_stop);
 295
 296         for (iter = iter_start; iter < iter_stop; iter++) {
 297                 struct static_key *iterk;
 298
 299                 iterk = (struct static_key *)(unsigned long)iter->key;
 300                 if (iterk == key)
 301                         continue;
 302
 303                 key = iterk;
 304                 if (__module_address(iter->key) == mod) {
 305                         /*
 306                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 307                          */
 308                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 309                         key->next = NULL;
 310                         continue;
 311                 }
 312                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 313                 if (!jlm)
 314                         return -ENOMEM;
 315                 jlm->mod = mod;
 316                 jlm->entries = iter;
 317                 jlm->next = key->next;
 318                 key->next = jlm;
 319
 320                 if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 321                         __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 322         }
 323
 324         return 0;
 325 }
 326
 327 static void jump_label_del_module(struct module *mod)
 328 {
 329         struct jump_entry *iter_start = mod->jump_entries;
 330         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 331         struct jump_entry *iter;
 332         struct static_key *key = NULL;
 333         struct static_key_mod *jlm, **prev;
 334
 335         for (iter = iter_start; iter < iter_stop; iter++) {
 336                 if (iter->key == (jump_label_t)(unsigned long)key)
 337                         continue;
 338
 339                 key = (struct static_key *)(unsigned long)iter->key;
 340
 341                 if (__module_address(iter->key) == mod)
 342                         continue;
 343
 344                 prev = &key->next;
 345                 jlm = key->next;
 346
 347                 while (jlm && jlm->mod != mod) {
 348                         prev = &jlm->next;
 349                         jlm = jlm->next;
 350                 }
 351
 352                 if (jlm) {
 353                         *prev = jlm->next;
 354                         kfree(jlm);
 355                 }
 356         }
 357 }
 358
 359 static void jump_label_invalidate_module_init(struct module *mod)
 360 {
 361         struct jump_entry *iter_start = mod->jump_entries;
 362         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 363         struct jump_entry *iter;
 364
 365         for (iter = iter_start; iter < iter_stop; iter++) {
 366                 if (within_module_init(iter->code, mod))
 367                         iter->code = 0;
 368         }
 369 }
 370
 371 static int
 372 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 373                          void *data)
 374 {
 375         struct module *mod = data;
 376         int ret = 0;
 377
 378         switch (val) {
 379         case MODULE_STATE_COMING:
 380                 jump_label_lock();
 381                 ret = jump_label_add_module(mod);
 382                 if (ret)
 383                         jump_label_del_module(mod);
 384                 jump_label_unlock();
 385                 break;
 386         case MODULE_STATE_GOING:
 387                 jump_label_lock();
 388                 jump_label_del_module(mod);
 389                 jump_label_unlock();
 390                 break;
 391         case MODULE_STATE_LIVE:
 392                 jump_label_lock();
 393                 jump_label_invalidate_module_init(mod);
 394                 jump_label_unlock();
 395                 break;
 396         }
 397
 398         return notifier_from_errno(ret);
 399 }
 400
 401 struct notifier_block jump_label_module_nb = {
 402         .notifier_call = jump_label_module_notify,
 403         .priority = 1, /* higher than tracepoints */
 404 };
 405
 406 static __init int jump_label_init_module(void)
 407 {
 408         return register_module_notifier(&jump_label_module_nb);
 409 }
 410 early_initcall(jump_label_init_module);
 411
 412 #endif /* CONFIG_MODULES */
 413
 414 /***
 415  * jump_label_text_reserved - check if addr range is reserved
 416  * @start: start text addr
 417  * @end: end text addr
 418  *
 419  * checks if the text addr located between @start and @end
 420  * overlaps with any of the jump label patch addresses. Code
 421  * that wants to modify kernel text should first verify that
 422  * it does not overlap with any of the jump label addresses.
 423  * Caller must hold jump_label_mutex.
 424  *
 425  * returns 1 if there is an overlap, 0 otherwise
 426  */
 427 int jump_label_text_reserved(void *start, void *end)
 428 {
 429         int ret = __jump_label_text_reserved(__start___jump_table,
 430                         __stop___jump_table, start, end);
 431
 432         if (ret)
 433                 return ret;
 434
 435 #ifdef CONFIG_MODULES
 436         ret = __jump_label_mod_text_reserved(start, end);
 437 #endif
 438         return ret;
 439 }
 440
 441 static void jump_label_update(struct static_key *key, int enable)
 442 {
 443         struct jump_entry *stop = __stop___jump_table;
 444         struct jump_entry *entry = jump_label_get_entries(key);
 445
 446 #ifdef CONFIG_MODULES
 447         struct module *mod = __module_address((unsigned long)key);
 448
 449         __jump_label_mod_update(key, enable);
 450
 451         if (mod)
 452                 stop = mod->jump_entries + mod->num_jump_entries;
 453 #endif
 454         /* if there are no users, entry can be NULL */
 455         if (entry)
 456                 __jump_label_update(key, entry, stop, enable);
 457 }
 458
 459 #endif