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 void jump_label_dec(struct jump_label_key *key)
  76 {
  77         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
  78                 return;
  79
  80         jump_label_update(key, JUMP_LABEL_DISABLE);
  81         jump_label_unlock();
  82 }
  83
  84 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
  85 {
  86         if (entry->code <= (unsigned long)end &&
  87                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
  88                 return 1;
  89
  90         return 0;
  91 }
  92
  93 static int __jump_label_text_reserved(struct jump_entry *iter_start,
  94                 struct jump_entry *iter_stop, void *start, void *end)
  95 {
  96         struct jump_entry *iter;
  97
  98         iter = iter_start;
  99         while (iter < iter_stop) {
 100                 if (addr_conflict(iter, start, end))
 101                         return 1;
 102                 iter++;
 103         }
 104
 105         return 0;
 106 }
 107
 108 /*
 109  * Update code which is definitely not currently executing.
 110  * Architectures which need heavyweight synchronization to modify
 111  * running code can override this to make the non-live update case
 112  * cheaper.
 113  */
 114 void __weak arch_jump_label_transform_static(struct jump_entry *entry,
 115                                             enum jump_label_type type)
 116 {
 117         arch_jump_label_transform(entry, type);
 118 }
 119
 120 static void __jump_label_update(struct jump_label_key *key,
 121                                 struct jump_entry *entry,
 122                                 struct jump_entry *stop, int enable)
 123 {
 124         for (; (entry < stop) &&
 125               (entry->key == (jump_label_t)(unsigned long)key);
 126               entry++) {
 127                 /*
 128                  * entry->code set to 0 invalidates module init text sections
 129                  * kernel_text_address() verifies we are not in core kernel
 130                  * init code, see jump_label_invalidate_module_init().
 131                  */
 132                 if (entry->code && kernel_text_address(entry->code))
 133                         arch_jump_label_transform(entry, enable);
 134         }
 135 }
 136
 137 void __init jump_label_init(void)
 138 {
 139         struct jump_entry *iter_start = __start___jump_table;
 140         struct jump_entry *iter_stop = __stop___jump_table;
 141         struct jump_label_key *key = NULL;
 142         struct jump_entry *iter;
 143
 144         jump_label_lock();
 145         jump_label_sort_entries(iter_start, iter_stop);
 146
 147         for (iter = iter_start; iter < iter_stop; iter++) {
 148                 struct jump_label_key *iterk;
 149
 150                 iterk = (struct jump_label_key *)(unsigned long)iter->key;
 151                 arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
 152                                                  JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
 153                 if (iterk == key)
 154                         continue;
 155
 156                 key = iterk;
 157                 key->entries = iter;
 158 #ifdef CONFIG_MODULES
 159                 key->next = NULL;
 160 #endif
 161         }
 162         jump_label_unlock();
 163 }
 164
 165 #ifdef CONFIG_MODULES
 166
 167 struct jump_label_mod {
 168         struct jump_label_mod *next;
 169         struct jump_entry *entries;
 170         struct module *mod;
 171 };
 172
 173 static int __jump_label_mod_text_reserved(void *start, void *end)
 174 {
 175         struct module *mod;
 176
 177         mod = __module_text_address((unsigned long)start);
 178         if (!mod)
 179                 return 0;
 180
 181         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 182
 183         return __jump_label_text_reserved(mod->jump_entries,
 184                                 mod->jump_entries + mod->num_jump_entries,
 185                                 start, end);
 186 }
 187
 188 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
 189 {
 190         struct jump_label_mod *mod = key->next;
 191
 192         while (mod) {
 193                 struct module *m = mod->mod;
 194
 195                 __jump_label_update(key, mod->entries,
 196                                     m->jump_entries + m->num_jump_entries,
 197                                     enable);
 198                 mod = mod->next;
 199         }
 200 }
 201
 202 /***
 203  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 204  * @mod: module to patch
 205  *
 206  * Allow for run-time selection of the optimal nops. Before the module
 207  * loads patch these with arch_get_jump_label_nop(), which is specified by
 208  * the arch specific jump label code.
 209  */
 210 void jump_label_apply_nops(struct module *mod)
 211 {
 212         struct jump_entry *iter_start = mod->jump_entries;
 213         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 214         struct jump_entry *iter;
 215
 216         /* if the module doesn't have jump label entries, just return */
 217         if (iter_start == iter_stop)
 218                 return;
 219
 220         for (iter = iter_start; iter < iter_stop; iter++)
 221                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 222 }
 223
 224 static int jump_label_add_module(struct module *mod)
 225 {
 226         struct jump_entry *iter_start = mod->jump_entries;
 227         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 228         struct jump_entry *iter;
 229         struct jump_label_key *key = NULL;
 230         struct jump_label_mod *jlm;
 231
 232         /* if the module doesn't have jump label entries, just return */
 233         if (iter_start == iter_stop)
 234                 return 0;
 235
 236         jump_label_sort_entries(iter_start, iter_stop);
 237
 238         for (iter = iter_start; iter < iter_stop; iter++) {
 239                 if (iter->key == (jump_label_t)(unsigned long)key)
 240                         continue;
 241
 242                 key = (struct jump_label_key *)(unsigned long)iter->key;
 243
 244                 if (__module_address(iter->key) == mod) {
 245                         atomic_set(&key->enabled, 0);
 246                         key->entries = iter;
 247                         key->next = NULL;
 248                         continue;
 249                 }
 250
 251                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
 252                 if (!jlm)
 253                         return -ENOMEM;
 254
 255                 jlm->mod = mod;
 256                 jlm->entries = iter;
 257                 jlm->next = key->next;
 258                 key->next = jlm;
 259
 260                 if (jump_label_enabled(key))
 261                         __jump_label_update(key, iter, iter_stop,
 262                                             JUMP_LABEL_ENABLE);
 263         }
 264
 265         return 0;
 266 }
 267
 268 static void jump_label_del_module(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         struct jump_label_key *key = NULL;
 274         struct jump_label_mod *jlm, **prev;
 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                         continue;
 284
 285                 prev = &key->next;
 286                 jlm = key->next;
 287
 288                 while (jlm && jlm->mod != mod) {
 289                         prev = &jlm->next;
 290                         jlm = jlm->next;
 291                 }
 292
 293                 if (jlm) {
 294                         *prev = jlm->next;
 295                         kfree(jlm);
 296                 }
 297         }
 298 }
 299
 300 static void jump_label_invalidate_module_init(struct module *mod)
 301 {
 302         struct jump_entry *iter_start = mod->jump_entries;
 303         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 304         struct jump_entry *iter;
 305
 306         for (iter = iter_start; iter < iter_stop; iter++) {
 307                 if (within_module_init(iter->code, mod))
 308                         iter->code = 0;
 309         }
 310 }
 311
 312 static int
 313 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 314                          void *data)
 315 {
 316         struct module *mod = data;
 317         int ret = 0;
 318
 319         switch (val) {
 320         case MODULE_STATE_COMING:
 321                 jump_label_lock();
 322                 ret = jump_label_add_module(mod);
 323                 if (ret)
 324                         jump_label_del_module(mod);
 325                 jump_label_unlock();
 326                 break;
 327         case MODULE_STATE_GOING:
 328                 jump_label_lock();
 329                 jump_label_del_module(mod);
 330                 jump_label_unlock();
 331                 break;
 332         case MODULE_STATE_LIVE:
 333                 jump_label_lock();
 334                 jump_label_invalidate_module_init(mod);
 335                 jump_label_unlock();
 336                 break;
 337         }
 338
 339         return notifier_from_errno(ret);
 340 }
 341
 342 struct notifier_block jump_label_module_nb = {
 343         .notifier_call = jump_label_module_notify,
 344         .priority = 1, /* higher than tracepoints */
 345 };
 346
 347 static __init int jump_label_init_module(void)
 348 {
 349         return register_module_notifier(&jump_label_module_nb);
 350 }
 351 early_initcall(jump_label_init_module);
 352
 353 #endif /* CONFIG_MODULES */
 354
 355 /***
 356  * jump_label_text_reserved - check if addr range is reserved
 357  * @start: start text addr
 358  * @end: end text addr
 359  *
 360  * checks if the text addr located between @start and @end
 361  * overlaps with any of the jump label patch addresses. Code
 362  * that wants to modify kernel text should first verify that
 363  * it does not overlap with any of the jump label addresses.
 364  * Caller must hold jump_label_mutex.
 365  *
 366  * returns 1 if there is an overlap, 0 otherwise
 367  */
 368 int jump_label_text_reserved(void *start, void *end)
 369 {
 370         int ret = __jump_label_text_reserved(__start___jump_table,
 371                         __stop___jump_table, start, end);
 372
 373         if (ret)
 374                 return ret;
 375
 376 #ifdef CONFIG_MODULES
 377         ret = __jump_label_mod_text_reserved(start, end);
 378 #endif
 379         return ret;
 380 }
 381
 382 static void jump_label_update(struct jump_label_key *key, int enable)
 383 {
 384         struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
 385
 386 #ifdef CONFIG_MODULES
 387         struct module *mod = __module_address((jump_label_t)key);
 388
 389         __jump_label_mod_update(key, enable);
 390
 391         if (mod)
 392                 stop = mod->jump_entries + mod->num_jump_entries;
 393 #endif
 394         /* if there are no users, entry can be NULL */
 395         if (entry)
 396                 __jump_label_update(key, entry, stop, enable);
 397 }
 398
 399 #endif