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_add_return(1, &key->enabled) == 1)
  70                 jump_label_update(key, JUMP_LABEL_ENABLE);
  71         jump_label_unlock();
  72 }
  73
  74 void jump_label_dec(struct jump_label_key *key)
  75 {
  76         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
  77                 return;
  78
  79         jump_label_update(key, JUMP_LABEL_DISABLE);
  80         jump_label_unlock();
  81 }
  82
  83 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
  84 {
  85         if (entry->code <= (unsigned long)end &&
  86                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
  87                 return 1;
  88
  89         return 0;
  90 }
  91
  92 static int __jump_label_text_reserved(struct jump_entry *iter_start,
  93                 struct jump_entry *iter_stop, void *start, void *end)
  94 {
  95         struct jump_entry *iter;
  96
  97         iter = iter_start;
  98         while (iter < iter_stop) {
  99                 if (addr_conflict(iter, start, end))
 100                         return 1;
 101                 iter++;
 102         }
 103
 104         return 0;
 105 }
 106
 107 /*
 108  * Update code which is definitely not currently executing.
 109  * Architectures which need heavyweight synchronization to modify
 110  * running code can override this to make the non-live update case
 111  * cheaper.
 112  */
 113 void __weak arch_jump_label_transform_static(struct jump_entry *entry,
 114                                             enum jump_label_type type)
 115 {
 116         arch_jump_label_transform(entry, type);
 117 }
 118
 119 static void __jump_label_update(struct jump_label_key *key,
 120                                 struct jump_entry *entry,
 121                                 struct jump_entry *stop, int enable)
 122 {
 123         for (; (entry < stop) &&
 124               (entry->key == (jump_label_t)(unsigned long)key);
 125               entry++) {
 126                 /*
 127                  * entry->code set to 0 invalidates module init text sections
 128                  * kernel_text_address() verifies we are not in core kernel
 129                  * init code, see jump_label_invalidate_module_init().
 130                  */
 131                 if (entry->code && kernel_text_address(entry->code))
 132                         arch_jump_label_transform(entry, enable);
 133         }
 134 }
 135
 136 static __init int jump_label_init(void)
 137 {
 138         struct jump_entry *iter_start = __start___jump_table;
 139         struct jump_entry *iter_stop = __stop___jump_table;
 140         struct jump_label_key *key = NULL;
 141         struct jump_entry *iter;
 142
 143         jump_label_lock();
 144         jump_label_sort_entries(iter_start, iter_stop);
 145
 146         for (iter = iter_start; iter < iter_stop; iter++) {
 147                 struct jump_label_key *iterk;
 148
 149                 iterk = (struct jump_label_key *)(unsigned long)iter->key;
 150                 arch_jump_label_transform_static(iter, jump_label_enabled(iterk) ?
 151                                                  JUMP_LABEL_ENABLE : JUMP_LABEL_DISABLE);
 152                 if (iterk == key)
 153                         continue;
 154
 155                 key = iterk;
 156                 key->entries = iter;
 157 #ifdef CONFIG_MODULES
 158                 key->next = NULL;
 159 #endif
 160         }
 161         jump_label_unlock();
 162
 163         return 0;
 164 }
 165 early_initcall(jump_label_init);
 166
 167 #ifdef CONFIG_MODULES
 168
 169 struct jump_label_mod {
 170         struct jump_label_mod *next;
 171         struct jump_entry *entries;
 172         struct module *mod;
 173 };
 174
 175 static int __jump_label_mod_text_reserved(void *start, void *end)
 176 {
 177         struct module *mod;
 178
 179         mod = __module_text_address((unsigned long)start);
 180         if (!mod)
 181                 return 0;
 182
 183         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 184
 185         return __jump_label_text_reserved(mod->jump_entries,
 186                                 mod->jump_entries + mod->num_jump_entries,
 187                                 start, end);
 188 }
 189
 190 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
 191 {
 192         struct jump_label_mod *mod = key->next;
 193
 194         while (mod) {
 195                 struct module *m = mod->mod;
 196
 197                 __jump_label_update(key, mod->entries,
 198                                     m->jump_entries + m->num_jump_entries,
 199                                     enable);
 200                 mod = mod->next;
 201         }
 202 }
 203
 204 /***
 205  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 206  * @mod: module to patch
 207  *
 208  * Allow for run-time selection of the optimal nops. Before the module
 209  * loads patch these with arch_get_jump_label_nop(), which is specified by
 210  * the arch specific jump label code.
 211  */
 212 void jump_label_apply_nops(struct module *mod)
 213 {
 214         struct jump_entry *iter_start = mod->jump_entries;
 215         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 216         struct jump_entry *iter;
 217
 218         /* if the module doesn't have jump label entries, just return */
 219         if (iter_start == iter_stop)
 220                 return;
 221
 222         for (iter = iter_start; iter < iter_stop; iter++)
 223                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 224 }
 225
 226 static int jump_label_add_module(struct module *mod)
 227 {
 228         struct jump_entry *iter_start = mod->jump_entries;
 229         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 230         struct jump_entry *iter;
 231         struct jump_label_key *key = NULL;
 232         struct jump_label_mod *jlm;
 233
 234         /* if the module doesn't have jump label entries, just return */
 235         if (iter_start == iter_stop)
 236                 return 0;
 237
 238         jump_label_sort_entries(iter_start, iter_stop);
 239
 240         for (iter = iter_start; iter < iter_stop; iter++) {
 241                 if (iter->key == (jump_label_t)(unsigned long)key)
 242                         continue;
 243
 244                 key = (struct jump_label_key *)(unsigned long)iter->key;
 245
 246                 if (__module_address(iter->key) == mod) {
 247                         atomic_set(&key->enabled, 0);
 248                         key->entries = iter;
 249                         key->next = NULL;
 250                         continue;
 251                 }
 252
 253                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
 254                 if (!jlm)
 255                         return -ENOMEM;
 256
 257                 jlm->mod = mod;
 258                 jlm->entries = iter;
 259                 jlm->next = key->next;
 260                 key->next = jlm;
 261
 262                 if (jump_label_enabled(key))
 263                         __jump_label_update(key, iter, iter_stop,
 264                                             JUMP_LABEL_ENABLE);
 265         }
 266
 267         return 0;
 268 }
 269
 270 static void jump_label_del_module(struct module *mod)
 271 {
 272         struct jump_entry *iter_start = mod->jump_entries;
 273         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 274         struct jump_entry *iter;
 275         struct jump_label_key *key = NULL;
 276         struct jump_label_mod *jlm, **prev;
 277
 278         for (iter = iter_start; iter < iter_stop; iter++) {
 279                 if (iter->key == (jump_label_t)(unsigned long)key)
 280                         continue;
 281
 282                 key = (struct jump_label_key *)(unsigned long)iter->key;
 283
 284                 if (__module_address(iter->key) == mod)
 285                         continue;
 286
 287                 prev = &key->next;
 288                 jlm = key->next;
 289
 290                 while (jlm && jlm->mod != mod) {
 291                         prev = &jlm->next;
 292                         jlm = jlm->next;
 293                 }
 294
 295                 if (jlm) {
 296                         *prev = jlm->next;
 297                         kfree(jlm);
 298                 }
 299         }
 300 }
 301
 302 static void jump_label_invalidate_module_init(struct module *mod)
 303 {
 304         struct jump_entry *iter_start = mod->jump_entries;
 305         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 306         struct jump_entry *iter;
 307
 308         for (iter = iter_start; iter < iter_stop; iter++) {
 309                 if (within_module_init(iter->code, mod))
 310                         iter->code = 0;
 311         }
 312 }
 313
 314 static int
 315 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 316                          void *data)
 317 {
 318         struct module *mod = data;
 319         int ret = 0;
 320
 321         switch (val) {
 322         case MODULE_STATE_COMING:
 323                 jump_label_lock();
 324                 ret = jump_label_add_module(mod);
 325                 if (ret)
 326                         jump_label_del_module(mod);
 327                 jump_label_unlock();
 328                 break;
 329         case MODULE_STATE_GOING:
 330                 jump_label_lock();
 331                 jump_label_del_module(mod);
 332                 jump_label_unlock();
 333                 break;
 334         case MODULE_STATE_LIVE:
 335                 jump_label_lock();
 336                 jump_label_invalidate_module_init(mod);
 337                 jump_label_unlock();
 338                 break;
 339         }
 340
 341         return notifier_from_errno(ret);
 342 }
 343
 344 struct notifier_block jump_label_module_nb = {
 345         .notifier_call = jump_label_module_notify,
 346         .priority = 1, /* higher than tracepoints */
 347 };
 348
 349 static __init int jump_label_init_module(void)
 350 {
 351         return register_module_notifier(&jump_label_module_nb);
 352 }
 353 early_initcall(jump_label_init_module);
 354
 355 #endif /* CONFIG_MODULES */
 356
 357 /***
 358  * jump_label_text_reserved - check if addr range is reserved
 359  * @start: start text addr
 360  * @end: end text addr
 361  *
 362  * checks if the text addr located between @start and @end
 363  * overlaps with any of the jump label patch addresses. Code
 364  * that wants to modify kernel text should first verify that
 365  * it does not overlap with any of the jump label addresses.
 366  * Caller must hold jump_label_mutex.
 367  *
 368  * returns 1 if there is an overlap, 0 otherwise
 369  */
 370 int jump_label_text_reserved(void *start, void *end)
 371 {
 372         int ret = __jump_label_text_reserved(__start___jump_table,
 373                         __stop___jump_table, start, end);
 374
 375         if (ret)
 376                 return ret;
 377
 378 #ifdef CONFIG_MODULES
 379         ret = __jump_label_mod_text_reserved(start, end);
 380 #endif
 381         return ret;
 382 }
 383
 384 static void jump_label_update(struct jump_label_key *key, int enable)
 385 {
 386         struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
 387
 388 #ifdef CONFIG_MODULES
 389         struct module *mod = __module_address((jump_label_t)key);
 390
 391         __jump_label_mod_update(key, enable);
 392
 393         if (mod)
 394                 stop = mod->jump_entries + mod->num_jump_entries;
 395 #endif
 396         /* if there are no users, entry can be NULL */
 397         if (entry)
 398                 __jump_label_update(key, entry, stop, enable);
 399 }
 400
 401 #endif