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