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