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 void __init 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
 164 #ifdef CONFIG_MODULES
 165
 166 struct jump_label_mod {
 167         struct jump_label_mod *next;
 168         struct jump_entry *entries;
 169         struct module *mod;
 170 };
 171
 172 static int __jump_label_mod_text_reserved(void *start, void *end)
 173 {
 174         struct module *mod;
 175
 176         mod = __module_text_address((unsigned long)start);
 177         if (!mod)
 178                 return 0;
 179
 180         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 181
 182         return __jump_label_text_reserved(mod->jump_entries,
 183                                 mod->jump_entries + mod->num_jump_entries,
 184                                 start, end);
 185 }
 186
 187 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
 188 {
 189         struct jump_label_mod *mod = key->next;
 190
 191         while (mod) {
 192                 struct module *m = mod->mod;
 193
 194                 __jump_label_update(key, mod->entries,
 195                                     m->jump_entries + m->num_jump_entries,
 196                                     enable);
 197                 mod = mod->next;
 198         }
 199 }
 200
 201 /***
 202  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 203  * @mod: module to patch
 204  *
 205  * Allow for run-time selection of the optimal nops. Before the module
 206  * loads patch these with arch_get_jump_label_nop(), which is specified by
 207  * the arch specific jump label code.
 208  */
 209 void jump_label_apply_nops(struct module *mod)
 210 {
 211         struct jump_entry *iter_start = mod->jump_entries;
 212         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 213         struct jump_entry *iter;
 214
 215         /* if the module doesn't have jump label entries, just return */
 216         if (iter_start == iter_stop)
 217                 return;
 218
 219         for (iter = iter_start; iter < iter_stop; iter++)
 220                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 221 }
 222
 223 static int jump_label_add_module(struct module *mod)
 224 {
 225         struct jump_entry *iter_start = mod->jump_entries;
 226         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 227         struct jump_entry *iter;
 228         struct jump_label_key *key = NULL;
 229         struct jump_label_mod *jlm;
 230
 231         /* if the module doesn't have jump label entries, just return */
 232         if (iter_start == iter_stop)
 233                 return 0;
 234
 235         jump_label_sort_entries(iter_start, iter_stop);
 236
 237         for (iter = iter_start; iter < iter_stop; iter++) {
 238                 if (iter->key == (jump_label_t)(unsigned long)key)
 239                         continue;
 240
 241                 key = (struct jump_label_key *)(unsigned long)iter->key;
 242
 243                 if (__module_address(iter->key) == mod) {
 244                         atomic_set(&key->enabled, 0);
 245                         key->entries = iter;
 246                         key->next = NULL;
 247                         continue;
 248                 }
 249
 250                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
 251                 if (!jlm)
 252                         return -ENOMEM;
 253
 254                 jlm->mod = mod;
 255                 jlm->entries = iter;
 256                 jlm->next = key->next;
 257                 key->next = jlm;
 258
 259                 if (jump_label_enabled(key))
 260                         __jump_label_update(key, iter, iter_stop,
 261                                             JUMP_LABEL_ENABLE);
 262         }
 263
 264         return 0;
 265 }
 266
 267 static void jump_label_del_module(struct module *mod)
 268 {
 269         struct jump_entry *iter_start = mod->jump_entries;
 270         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 271         struct jump_entry *iter;
 272         struct jump_label_key *key = NULL;
 273         struct jump_label_mod *jlm, **prev;
 274
 275         for (iter = iter_start; iter < iter_stop; iter++) {
 276                 if (iter->key == (jump_label_t)(unsigned long)key)
 277                         continue;
 278
 279                 key = (struct jump_label_key *)(unsigned long)iter->key;
 280
 281                 if (__module_address(iter->key) == mod)
 282                         continue;
 283
 284                 prev = &key->next;
 285                 jlm = key->next;
 286
 287                 while (jlm && jlm->mod != mod) {
 288                         prev = &jlm->next;
 289                         jlm = jlm->next;
 290                 }
 291
 292                 if (jlm) {
 293                         *prev = jlm->next;
 294                         kfree(jlm);
 295                 }
 296         }
 297 }
 298
 299 static void jump_label_invalidate_module_init(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
 305         for (iter = iter_start; iter < iter_stop; iter++) {
 306                 if (within_module_init(iter->code, mod))
 307                         iter->code = 0;
 308         }
 309 }
 310
 311 static int
 312 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 313                          void *data)
 314 {
 315         struct module *mod = data;
 316         int ret = 0;
 317
 318         switch (val) {
 319         case MODULE_STATE_COMING:
 320                 jump_label_lock();
 321                 ret = jump_label_add_module(mod);
 322                 if (ret)
 323                         jump_label_del_module(mod);
 324                 jump_label_unlock();
 325                 break;
 326         case MODULE_STATE_GOING:
 327                 jump_label_lock();
 328                 jump_label_del_module(mod);
 329                 jump_label_unlock();
 330                 break;
 331         case MODULE_STATE_LIVE:
 332                 jump_label_lock();
 333                 jump_label_invalidate_module_init(mod);
 334                 jump_label_unlock();
 335                 break;
 336         }
 337
 338         return notifier_from_errno(ret);
 339 }
 340
 341 struct notifier_block jump_label_module_nb = {
 342         .notifier_call = jump_label_module_notify,
 343         .priority = 1, /* higher than tracepoints */
 344 };
 345
 346 static __init int jump_label_init_module(void)
 347 {
 348         return register_module_notifier(&jump_label_module_nb);
 349 }
 350 early_initcall(jump_label_init_module);
 351
 352 #endif /* CONFIG_MODULES */
 353
 354 /***
 355  * jump_label_text_reserved - check if addr range is reserved
 356  * @start: start text addr
 357  * @end: end text addr
 358  *
 359  * checks if the text addr located between @start and @end
 360  * overlaps with any of the jump label patch addresses. Code
 361  * that wants to modify kernel text should first verify that
 362  * it does not overlap with any of the jump label addresses.
 363  * Caller must hold jump_label_mutex.
 364  *
 365  * returns 1 if there is an overlap, 0 otherwise
 366  */
 367 int jump_label_text_reserved(void *start, void *end)
 368 {
 369         int ret = __jump_label_text_reserved(__start___jump_table,
 370                         __stop___jump_table, start, end);
 371
 372         if (ret)
 373                 return ret;
 374
 375 #ifdef CONFIG_MODULES
 376         ret = __jump_label_mod_text_reserved(start, end);
 377 #endif
 378         return ret;
 379 }
 380
 381 static void jump_label_update(struct jump_label_key *key, int enable)
 382 {
 383         struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
 384
 385 #ifdef CONFIG_MODULES
 386         struct module *mod = __module_address((jump_label_t)key);
 387
 388         __jump_label_mod_update(key, enable);
 389
 390         if (mod)
 391                 stop = mod->jump_entries + mod->num_jump_entries;
 392 #endif
 393         /* if there are no users, entry can be NULL */
 394         if (entry)
 395                 __jump_label_update(key, entry, stop, enable);
 396 }
 397
 398 #endif