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