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