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