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 static int jump_label_cmp(const void *a, const void *b)
  33 {
  34         const struct jump_entry *jea = a;
  35         const struct jump_entry *jeb = b;
  36
  37         if (jea->key < jeb->key)
  38                 return -1;
  39
  40         if (jea->key > jeb->key)
  41                 return 1;
  42
  43         return 0;
  44 }
  45
  46 static void
  47 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
  48 {
  49         unsigned long size;
  50
  51         size = (((unsigned long)stop - (unsigned long)start)
  52                                         / sizeof(struct jump_entry));
  53         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  54 }
  55
  56 static void jump_label_update(struct static_key *key, int enable);
  57
  58 void static_key_slow_inc(struct static_key *key)
  59 {
  60         if (atomic_inc_not_zero(&key->enabled))
  61                 return;
  62
  63         jump_label_lock();
  64         if (atomic_read(&key->enabled) == 0) {
  65                 if (!jump_label_get_branch_default(key))
  66                         jump_label_update(key, JUMP_LABEL_ENABLE);
  67                 else
  68                         jump_label_update(key, JUMP_LABEL_DISABLE);
  69         }
  70         atomic_inc(&key->enabled);
  71         jump_label_unlock();
  72 }
  73 EXPORT_SYMBOL_GPL(static_key_slow_inc);
  74
  75 static void __static_key_slow_dec(struct static_key *key,
  76                 unsigned long rate_limit, struct delayed_work *work)
  77 {
  78         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
  79                 WARN(atomic_read(&key->enabled) < 0,
  80                      "jump label: negative count!\n");
  81                 return;
  82         }
  83
  84         if (rate_limit) {
  85                 atomic_inc(&key->enabled);
  86                 schedule_delayed_work(work, rate_limit);
  87         } else {
  88                 if (!jump_label_get_branch_default(key))
  89                         jump_label_update(key, JUMP_LABEL_DISABLE);
  90                 else
  91                         jump_label_update(key, JUMP_LABEL_ENABLE);
  92         }
  93         jump_label_unlock();
  94 }
  95
  96 static void jump_label_update_timeout(struct work_struct *work)
  97 {
  98         struct static_key_deferred *key =
  99                 container_of(work, struct static_key_deferred, work.work);
 100         __static_key_slow_dec(&key->key, 0, NULL);
 101 }
 102
 103 void static_key_slow_dec(struct static_key *key)
 104 {
 105         __static_key_slow_dec(key, 0, NULL);
 106 }
 107 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 108
 109 void static_key_slow_dec_deferred(struct static_key_deferred *key)
 110 {
 111         __static_key_slow_dec(&key->key, key->timeout, &key->work);
 112 }
 113 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 114
 115 void jump_label_rate_limit(struct static_key_deferred *key,
 116                 unsigned long rl)
 117 {
 118         key->timeout = rl;
 119         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 120 }
 121 EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 122
 123 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 124 {
 125         if (entry->code <= (unsigned long)end &&
 126                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 127                 return 1;
 128
 129         return 0;
 130 }
 131
 132 static int __jump_label_text_reserved(struct jump_entry *iter_start,
 133                 struct jump_entry *iter_stop, void *start, void *end)
 134 {
 135         struct jump_entry *iter;
 136
 137         iter = iter_start;
 138         while (iter < iter_stop) {
 139                 if (addr_conflict(iter, start, end))
 140                         return 1;
 141                 iter++;
 142         }
 143
 144         return 0;
 145 }
 146
 147 /*
 148  * Update code which is definitely not currently executing.
 149  * Architectures which need heavyweight synchronization to modify
 150  * running code can override this to make the non-live update case
 151  * cheaper.
 152  */
 153 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 154                                             enum jump_label_type type)
 155 {
 156         arch_jump_label_transform(entry, type);
 157 }
 158
 159 static void __jump_label_update(struct static_key *key,
 160                                 struct jump_entry *entry,
 161                                 struct jump_entry *stop, int enable)
 162 {
 163         for (; (entry < stop) &&
 164               (entry->key == (jump_label_t)(unsigned long)key);
 165               entry++) {
 166                 /*
 167                  * entry->code set to 0 invalidates module init text sections
 168                  * kernel_text_address() verifies we are not in core kernel
 169                  * init code, see jump_label_invalidate_module_init().
 170                  */
 171                 if (entry->code && kernel_text_address(entry->code))
 172                         arch_jump_label_transform(entry, enable);
 173         }
 174 }
 175
 176 static enum jump_label_type jump_label_type(struct static_key *key)
 177 {
 178         bool true_branch = jump_label_get_branch_default(key);
 179         bool state = static_key_enabled(key);
 180
 181         if ((!true_branch && state) || (true_branch && !state))
 182                 return JUMP_LABEL_ENABLE;
 183
 184         return JUMP_LABEL_DISABLE;
 185 }
 186
 187 void __init jump_label_init(void)
 188 {
 189         struct jump_entry *iter_start = __start___jump_table;
 190         struct jump_entry *iter_stop = __stop___jump_table;
 191         struct static_key *key = NULL;
 192         struct jump_entry *iter;
 193
 194         jump_label_lock();
 195         jump_label_sort_entries(iter_start, iter_stop);
 196
 197         for (iter = iter_start; iter < iter_stop; iter++) {
 198                 struct static_key *iterk;
 199
 200                 iterk = (struct static_key *)(unsigned long)iter->key;
 201                 arch_jump_label_transform_static(iter, jump_label_type(iterk));
 202                 if (iterk == key)
 203                         continue;
 204
 205                 key = iterk;
 206                 /*
 207                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 208                  */
 209                 *((unsigned long *)&key->entries) += (unsigned long)iter;
 210 #ifdef CONFIG_MODULES
 211                 key->next = NULL;
 212 #endif
 213         }
 214         jump_label_unlock();
 215 }
 216
 217 #ifdef CONFIG_MODULES
 218
 219 struct static_key_mod {
 220         struct static_key_mod *next;
 221         struct jump_entry *entries;
 222         struct module *mod;
 223 };
 224
 225 static int __jump_label_mod_text_reserved(void *start, void *end)
 226 {
 227         struct module *mod;
 228
 229         mod = __module_text_address((unsigned long)start);
 230         if (!mod)
 231                 return 0;
 232
 233         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 234
 235         return __jump_label_text_reserved(mod->jump_entries,
 236                                 mod->jump_entries + mod->num_jump_entries,
 237                                 start, end);
 238 }
 239
 240 static void __jump_label_mod_update(struct static_key *key, int enable)
 241 {
 242         struct static_key_mod *mod = key->next;
 243
 244         while (mod) {
 245                 struct module *m = mod->mod;
 246
 247                 __jump_label_update(key, mod->entries,
 248                                     m->jump_entries + m->num_jump_entries,
 249                                     enable);
 250                 mod = mod->next;
 251         }
 252 }
 253
 254 /***
 255  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 256  * @mod: module to patch
 257  *
 258  * Allow for run-time selection of the optimal nops. Before the module
 259  * loads patch these with arch_get_jump_label_nop(), which is specified by
 260  * the arch specific jump label code.
 261  */
 262 void jump_label_apply_nops(struct module *mod)
 263 {
 264         struct jump_entry *iter_start = mod->jump_entries;
 265         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 266         struct jump_entry *iter;
 267
 268         /* if the module doesn't have jump label entries, just return */
 269         if (iter_start == iter_stop)
 270                 return;
 271
 272         for (iter = iter_start; iter < iter_stop; iter++) {
 273                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 274         }
 275 }
 276
 277 static int jump_label_add_module(struct module *mod)
 278 {
 279         struct jump_entry *iter_start = mod->jump_entries;
 280         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 281         struct jump_entry *iter;
 282         struct static_key *key = NULL;
 283         struct static_key_mod *jlm;
 284
 285         /* if the module doesn't have jump label entries, just return */
 286         if (iter_start == iter_stop)
 287                 return 0;
 288
 289         jump_label_sort_entries(iter_start, iter_stop);
 290
 291         for (iter = iter_start; iter < iter_stop; iter++) {
 292                 struct static_key *iterk;
 293
 294                 iterk = (struct static_key *)(unsigned long)iter->key;
 295                 if (iterk == key)
 296                         continue;
 297
 298                 key = iterk;
 299                 if (__module_address(iter->key) == mod) {
 300                         /*
 301                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 302                          */
 303                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 304                         key->next = NULL;
 305                         continue;
 306                 }
 307                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 308                 if (!jlm)
 309                         return -ENOMEM;
 310                 jlm->mod = mod;
 311                 jlm->entries = iter;
 312                 jlm->next = key->next;
 313                 key->next = jlm;
 314
 315                 if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 316                         __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 317         }
 318
 319         return 0;
 320 }
 321
 322 static void jump_label_del_module(struct module *mod)
 323 {
 324         struct jump_entry *iter_start = mod->jump_entries;
 325         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 326         struct jump_entry *iter;
 327         struct static_key *key = NULL;
 328         struct static_key_mod *jlm, **prev;
 329
 330         for (iter = iter_start; iter < iter_stop; iter++) {
 331                 if (iter->key == (jump_label_t)(unsigned long)key)
 332                         continue;
 333
 334                 key = (struct static_key *)(unsigned long)iter->key;
 335
 336                 if (__module_address(iter->key) == mod)
 337                         continue;
 338
 339                 prev = &key->next;
 340                 jlm = key->next;
 341
 342                 while (jlm && jlm->mod != mod) {
 343                         prev = &jlm->next;
 344                         jlm = jlm->next;
 345                 }
 346
 347                 if (jlm) {
 348                         *prev = jlm->next;
 349                         kfree(jlm);
 350                 }
 351         }
 352 }
 353
 354 static void jump_label_invalidate_module_init(struct module *mod)
 355 {
 356         struct jump_entry *iter_start = mod->jump_entries;
 357         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 358         struct jump_entry *iter;
 359
 360         for (iter = iter_start; iter < iter_stop; iter++) {
 361                 if (within_module_init(iter->code, mod))
 362                         iter->code = 0;
 363         }
 364 }
 365
 366 static int
 367 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 368                          void *data)
 369 {
 370         struct module *mod = data;
 371         int ret = 0;
 372
 373         switch (val) {
 374         case MODULE_STATE_COMING:
 375                 jump_label_lock();
 376                 ret = jump_label_add_module(mod);
 377                 if (ret)
 378                         jump_label_del_module(mod);
 379                 jump_label_unlock();
 380                 break;
 381         case MODULE_STATE_GOING:
 382                 jump_label_lock();
 383                 jump_label_del_module(mod);
 384                 jump_label_unlock();
 385                 break;
 386         case MODULE_STATE_LIVE:
 387                 jump_label_lock();
 388                 jump_label_invalidate_module_init(mod);
 389                 jump_label_unlock();
 390                 break;
 391         }
 392
 393         return notifier_from_errno(ret);
 394 }
 395
 396 struct notifier_block jump_label_module_nb = {
 397         .notifier_call = jump_label_module_notify,
 398         .priority = 1, /* higher than tracepoints */
 399 };
 400
 401 static __init int jump_label_init_module(void)
 402 {
 403         return register_module_notifier(&jump_label_module_nb);
 404 }
 405 early_initcall(jump_label_init_module);
 406
 407 #endif /* CONFIG_MODULES */
 408
 409 /***
 410  * jump_label_text_reserved - check if addr range is reserved
 411  * @start: start text addr
 412  * @end: end text addr
 413  *
 414  * checks if the text addr located between @start and @end
 415  * overlaps with any of the jump label patch addresses. Code
 416  * that wants to modify kernel text should first verify that
 417  * it does not overlap with any of the jump label addresses.
 418  * Caller must hold jump_label_mutex.
 419  *
 420  * returns 1 if there is an overlap, 0 otherwise
 421  */
 422 int jump_label_text_reserved(void *start, void *end)
 423 {
 424         int ret = __jump_label_text_reserved(__start___jump_table,
 425                         __stop___jump_table, start, end);
 426
 427         if (ret)
 428                 return ret;
 429
 430 #ifdef CONFIG_MODULES
 431         ret = __jump_label_mod_text_reserved(start, end);
 432 #endif
 433         return ret;
 434 }
 435
 436 static void jump_label_update(struct static_key *key, int enable)
 437 {
 438         struct jump_entry *stop = __stop___jump_table;
 439         struct jump_entry *entry = jump_label_get_entries(key);
 440
 441 #ifdef CONFIG_MODULES
 442         struct module *mod = __module_address((unsigned long)key);
 443
 444         __jump_label_mod_update(key, enable);
 445
 446         if (mod)
 447                 stop = mod->jump_entries + mod->num_jump_entries;
 448 #endif
 449         /* if there are no users, entry can be NULL */
 450         if (entry)
 451                 __jump_label_update(key, entry, stop, enable);
 452 }
 453
 454 #endif