kernel/jump_label.c

   1 /*
   2  * jump label support
   3  *
   4  * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
   5  *
   6  */
   7 #include <linux/jump_label.h>
   8 #include <linux/memory.h>
   9 #include <linux/uaccess.h>
  10 #include <linux/module.h>
  11 #include <linux/list.h>
  12 #include <linux/jhash.h>
  13 #include <linux/slab.h>
  14 #include <linux/sort.h>
  15 #include <linux/err.h>
  16
  17 #ifdef HAVE_JUMP_LABEL
  18
  19 #define JUMP_LABEL_HASH_BITS 6
  20 #define JUMP_LABEL_TABLE_SIZE (1 << JUMP_LABEL_HASH_BITS)
  21 static struct hlist_head jump_label_table[JUMP_LABEL_TABLE_SIZE];
  22
  23 /* mutex to protect coming/going of the the jump_label table */
  24 static DEFINE_MUTEX(jump_label_mutex);
  25
  26 struct jump_label_entry {
  27         struct hlist_node hlist;
  28         struct jump_entry *table;
  29         int nr_entries;
  30         /* hang modules off here */
  31         struct hlist_head modules;
  32         unsigned long key;
  33 };
  34
  35 struct jump_label_module_entry {
  36         struct hlist_node hlist;
  37         struct jump_entry *table;
  38         int nr_entries;
  39         struct module *mod;
  40 };
  41
  42 void jump_label_lock(void)
  43 {
  44         mutex_lock(&jump_label_mutex);
  45 }
  46
  47 void jump_label_unlock(void)
  48 {
  49         mutex_unlock(&jump_label_mutex);
  50 }
  51
  52 static int jump_label_cmp(const void *a, const void *b)
  53 {
  54         const struct jump_entry *jea = a;
  55         const struct jump_entry *jeb = b;
  56
  57         if (jea->key < jeb->key)
  58                 return -1;
  59
  60         if (jea->key > jeb->key)
  61                 return 1;
  62
  63         return 0;
  64 }
  65
  66 static void
  67 sort_jump_label_entries(struct jump_entry *start, struct jump_entry *stop)
  68 {
  69         unsigned long size;
  70
  71         size = (((unsigned long)stop - (unsigned long)start)
  72                                         / sizeof(struct jump_entry));
  73         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  74 }
  75
  76 static struct jump_label_entry *get_jump_label_entry(jump_label_t key)
  77 {
  78         struct hlist_head *head;
  79         struct hlist_node *node;
  80         struct jump_label_entry *e;
  81         u32 hash = jhash((void *)&key, sizeof(jump_label_t), 0);
  82
  83         head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
  84         hlist_for_each_entry(e, node, head, hlist) {
  85                 if (key == e->key)
  86                         return e;
  87         }
  88         return NULL;
  89 }
  90
  91 static struct jump_label_entry *
  92 add_jump_label_entry(jump_label_t key, int nr_entries, struct jump_entry *table)
  93 {
  94         struct hlist_head *head;
  95         struct jump_label_entry *e;
  96         u32 hash;
  97
  98         e = get_jump_label_entry(key);
  99         if (e)
 100                 return ERR_PTR(-EEXIST);
 101
 102         e = kmalloc(sizeof(struct jump_label_entry), GFP_KERNEL);
 103         if (!e)
 104                 return ERR_PTR(-ENOMEM);
 105
 106         hash = jhash((void *)&key, sizeof(jump_label_t), 0);
 107         head = &jump_label_table[hash & (JUMP_LABEL_TABLE_SIZE - 1)];
 108         e->key = key;
 109         e->table = table;
 110         e->nr_entries = nr_entries;
 111         INIT_HLIST_HEAD(&(e->modules));
 112         hlist_add_head(&e->hlist, head);
 113         return e;
 114 }
 115
 116 static int
 117 build_jump_label_hashtable(struct jump_entry *start, struct jump_entry *stop)
 118 {
 119         struct jump_entry *iter, *iter_begin;
 120         struct jump_label_entry *entry;
 121         int count;
 122
 123         sort_jump_label_entries(start, stop);
 124         iter = start;
 125         while (iter < stop) {
 126                 entry = get_jump_label_entry(iter->key);
 127                 if (!entry) {
 128                         iter_begin = iter;
 129                         count = 0;
 130                         while ((iter < stop) &&
 131                                 (iter->key == iter_begin->key)) {
 132                                 iter++;
 133                                 count++;
 134                         }
 135                         entry = add_jump_label_entry(iter_begin->key,
 136                                                         count, iter_begin);
 137                         if (IS_ERR(entry))
 138                                 return PTR_ERR(entry);
 139                  } else {
 140                         WARN_ONCE(1, KERN_ERR "build_jump_hashtable: unexpected entry!\n");
 141                         return -1;
 142                 }
 143         }
 144         return 0;
 145 }
 146
 147 /***
 148  * jump_label_update - update jump label text
 149  * @key -  key value associated with a a jump label
 150  * @type - enum set to JUMP_LABEL_ENABLE or JUMP_LABEL_DISABLE
 151  *
 152  * Will enable/disable the jump for jump label @key, depending on the
 153  * value of @type.
 154  *
 155  */
 156
 157 void jump_label_update(unsigned long key, enum jump_label_type type)
 158 {
 159         struct jump_entry *iter;
 160         struct jump_label_entry *entry;
 161         struct hlist_node *module_node;
 162         struct jump_label_module_entry *e_module;
 163         int count;
 164
 165         jump_label_lock();
 166         entry = get_jump_label_entry((jump_label_t)key);
 167         if (entry) {
 168                 count = entry->nr_entries;
 169                 iter = entry->table;
 170                 while (count--) {
 171                         if (kernel_text_address(iter->code))
 172                                 arch_jump_label_transform(iter, type);
 173                         iter++;
 174                 }
 175                 /* eanble/disable jump labels in modules */
 176                 hlist_for_each_entry(e_module, module_node, &(entry->modules),
 177                                                         hlist) {
 178                         count = e_module->nr_entries;
 179                         iter = e_module->table;
 180                         while (count--) {
 181                                 if (iter->key &&
 182                                                 kernel_text_address(iter->code))
 183                                         arch_jump_label_transform(iter, type);
 184                                 iter++;
 185                         }
 186                 }
 187         }
 188         jump_label_unlock();
 189 }
 190
 191 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 192 {
 193         if (entry->code <= (unsigned long)end &&
 194                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 195                 return 1;
 196
 197         return 0;
 198 }
 199
 200 #ifdef CONFIG_MODULES
 201
 202 static int module_conflict(void *start, void *end)
 203 {
 204         struct hlist_head *head;
 205         struct hlist_node *node, *node_next, *module_node, *module_node_next;
 206         struct jump_label_entry *e;
 207         struct jump_label_module_entry *e_module;
 208         struct jump_entry *iter;
 209         int i, count;
 210         int conflict = 0;
 211
 212         for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
 213                 head = &jump_label_table[i];
 214                 hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
 215                         hlist_for_each_entry_safe(e_module, module_node,
 216                                                         module_node_next,
 217                                                         &(e->modules), hlist) {
 218                                 count = e_module->nr_entries;
 219                                 iter = e_module->table;
 220                                 while (count--) {
 221                                         if (addr_conflict(iter, start, end)) {
 222                                                 conflict = 1;
 223                                                 goto out;
 224                                         }
 225                                         iter++;
 226                                 }
 227                         }
 228                 }
 229         }
 230 out:
 231         return conflict;
 232 }
 233
 234 #endif
 235
 236 /***
 237  * jump_label_text_reserved - check if addr range is reserved
 238  * @start: start text addr
 239  * @end: end text addr
 240  *
 241  * checks if the text addr located between @start and @end
 242  * overlaps with any of the jump label patch addresses. Code
 243  * that wants to modify kernel text should first verify that
 244  * it does not overlap with any of the jump label addresses.
 245  * Caller must hold jump_label_mutex.
 246  *
 247  * returns 1 if there is an overlap, 0 otherwise
 248  */
 249 int jump_label_text_reserved(void *start, void *end)
 250 {
 251         struct jump_entry *iter;
 252         struct jump_entry *iter_start = __start___jump_table;
 253         struct jump_entry *iter_stop = __start___jump_table;
 254         int conflict = 0;
 255
 256         iter = iter_start;
 257         while (iter < iter_stop) {
 258                 if (addr_conflict(iter, start, end)) {
 259                         conflict = 1;
 260                         goto out;
 261                 }
 262                 iter++;
 263         }
 264
 265         /* now check modules */
 266 #ifdef CONFIG_MODULES
 267         conflict = module_conflict(start, end);
 268 #endif
 269 out:
 270         return conflict;
 271 }
 272
 273 static __init int init_jump_label(void)
 274 {
 275         int ret;
 276         struct jump_entry *iter_start = __start___jump_table;
 277         struct jump_entry *iter_stop = __stop___jump_table;
 278         struct jump_entry *iter;
 279
 280         jump_label_lock();
 281         ret = build_jump_label_hashtable(__start___jump_table,
 282                                          __stop___jump_table);
 283         iter = iter_start;
 284         while (iter < iter_stop) {
 285                 arch_jump_label_text_poke_early(iter->code);
 286                 iter++;
 287         }
 288         jump_label_unlock();
 289         return ret;
 290 }
 291 early_initcall(init_jump_label);
 292
 293 #ifdef CONFIG_MODULES
 294
 295 static struct jump_label_module_entry *
 296 add_jump_label_module_entry(struct jump_label_entry *entry,
 297                             struct jump_entry *iter_begin,
 298                             int count, struct module *mod)
 299 {
 300         struct jump_label_module_entry *e;
 301
 302         e = kmalloc(sizeof(struct jump_label_module_entry), GFP_KERNEL);
 303         if (!e)
 304                 return ERR_PTR(-ENOMEM);
 305         e->mod = mod;
 306         e->nr_entries = count;
 307         e->table = iter_begin;
 308         hlist_add_head(&e->hlist, &entry->modules);
 309         return e;
 310 }
 311
 312 static int add_jump_label_module(struct module *mod)
 313 {
 314         struct jump_entry *iter, *iter_begin;
 315         struct jump_label_entry *entry;
 316         struct jump_label_module_entry *module_entry;
 317         int count;
 318
 319         /* if the module doesn't have jump label entries, just return */
 320         if (!mod->num_jump_entries)
 321                 return 0;
 322
 323         sort_jump_label_entries(mod->jump_entries,
 324                                 mod->jump_entries + mod->num_jump_entries);
 325         iter = mod->jump_entries;
 326         while (iter < mod->jump_entries + mod->num_jump_entries) {
 327                 entry = get_jump_label_entry(iter->key);
 328                 iter_begin = iter;
 329                 count = 0;
 330                 while ((iter < mod->jump_entries + mod->num_jump_entries) &&
 331                         (iter->key == iter_begin->key)) {
 332                                 iter++;
 333                                 count++;
 334                 }
 335                 if (!entry) {
 336                         entry = add_jump_label_entry(iter_begin->key, 0, NULL);
 337                         if (IS_ERR(entry))
 338                                 return PTR_ERR(entry);
 339                 }
 340                 module_entry = add_jump_label_module_entry(entry, iter_begin,
 341                                                            count, mod);
 342                 if (IS_ERR(module_entry))
 343                         return PTR_ERR(module_entry);
 344         }
 345         return 0;
 346 }
 347
 348 static void remove_jump_label_module(struct module *mod)
 349 {
 350         struct hlist_head *head;
 351         struct hlist_node *node, *node_next, *module_node, *module_node_next;
 352         struct jump_label_entry *e;
 353         struct jump_label_module_entry *e_module;
 354         int i;
 355
 356         /* if the module doesn't have jump label entries, just return */
 357         if (!mod->num_jump_entries)
 358                 return;
 359
 360         for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
 361                 head = &jump_label_table[i];
 362                 hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
 363                         hlist_for_each_entry_safe(e_module, module_node,
 364                                                   module_node_next,
 365                                                   &(e->modules), hlist) {
 366                                 if (e_module->mod == mod) {
 367                                         hlist_del(&e_module->hlist);
 368                                         kfree(e_module);
 369                                 }
 370                         }
 371                         if (hlist_empty(&e->modules) && (e->nr_entries == 0)) {
 372                                 hlist_del(&e->hlist);
 373                                 kfree(e);
 374                         }
 375                 }
 376         }
 377 }
 378
 379 static void remove_jump_label_module_init(struct module *mod)
 380 {
 381         struct hlist_head *head;
 382         struct hlist_node *node, *node_next, *module_node, *module_node_next;
 383         struct jump_label_entry *e;
 384         struct jump_label_module_entry *e_module;
 385         struct jump_entry *iter;
 386         int i, count;
 387
 388         /* if the module doesn't have jump label entries, just return */
 389         if (!mod->num_jump_entries)
 390                 return;
 391
 392         for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
 393                 head = &jump_label_table[i];
 394                 hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
 395                         hlist_for_each_entry_safe(e_module, module_node,
 396                                                   module_node_next,
 397                                                   &(e->modules), hlist) {
 398                                 if (e_module->mod != mod)
 399                                         continue;
 400                                 count = e_module->nr_entries;
 401                                 iter = e_module->table;
 402                                 while (count--) {
 403                                         if (within_module_init(iter->code, mod))
 404                                                 iter->key = 0;
 405                                         iter++;
 406                                 }
 407                         }
 408                 }
 409         }
 410 }
 411
 412 static int
 413 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 414                          void *data)
 415 {
 416         struct module *mod = data;
 417         int ret = 0;
 418
 419         switch (val) {
 420         case MODULE_STATE_COMING:
 421                 jump_label_lock();
 422                 ret = add_jump_label_module(mod);
 423                 if (ret)
 424                         remove_jump_label_module(mod);
 425                 jump_label_unlock();
 426                 break;
 427         case MODULE_STATE_GOING:
 428                 jump_label_lock();
 429                 remove_jump_label_module(mod);
 430                 jump_label_unlock();
 431                 break;
 432         case MODULE_STATE_LIVE:
 433                 jump_label_lock();
 434                 remove_jump_label_module_init(mod);
 435                 jump_label_unlock();
 436                 break;
 437         }
 438         return ret;
 439 }
 440
 441 /***
 442  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 443  * @mod: module to patch
 444  *
 445  * Allow for run-time selection of the optimal nops. Before the module
 446  * loads patch these with arch_get_jump_label_nop(), which is specified by
 447  * the arch specific jump label code.
 448  */
 449 void jump_label_apply_nops(struct module *mod)
 450 {
 451         struct jump_entry *iter;
 452
 453         /* if the module doesn't have jump label entries, just return */
 454         if (!mod->num_jump_entries)
 455                 return;
 456
 457         iter = mod->jump_entries;
 458         while (iter < mod->jump_entries + mod->num_jump_entries) {
 459                 arch_jump_label_text_poke_early(iter->code);
 460                 iter++;
 461         }
 462 }
 463
 464 struct notifier_block jump_label_module_nb = {
 465         .notifier_call = jump_label_module_notify,
 466         .priority = 0,
 467 };
 468
 469 static __init int init_jump_label_module(void)
 470 {
 471         return register_module_notifier(&jump_label_module_nb);
 472 }
 473 early_initcall(init_jump_label_module);
 474
 475 #endif /* CONFIG_MODULES */
 476
 477 #endif