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 (kernel_text_address(iter->code))
 172                                         arch_jump_label_transform(iter, type);
 173                                 iter++;
 174                         }
 175                 }
 176         }
 177         mutex_unlock(&jump_label_mutex);
 178 }
 179
 180 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 181 {
 182         if (entry->code <= (unsigned long)end &&
 183                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 184                 return 1;
 185
 186         return 0;
 187 }
 188
 189 #ifdef CONFIG_MODULES
 190
 191 static int module_conflict(void *start, void *end)
 192 {
 193         struct hlist_head *head;
 194         struct hlist_node *node, *node_next, *module_node, *module_node_next;
 195         struct jump_label_entry *e;
 196         struct jump_label_module_entry *e_module;
 197         struct jump_entry *iter;
 198         int i, count;
 199         int conflict = 0;
 200
 201         for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
 202                 head = &jump_label_table[i];
 203                 hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
 204                         hlist_for_each_entry_safe(e_module, module_node,
 205                                                         module_node_next,
 206                                                         &(e->modules), hlist) {
 207                                 count = e_module->nr_entries;
 208                                 iter = e_module->table;
 209                                 while (count--) {
 210                                         if (addr_conflict(iter, start, end)) {
 211                                                 conflict = 1;
 212                                                 goto out;
 213                                         }
 214                                         iter++;
 215                                 }
 216                         }
 217                 }
 218         }
 219 out:
 220         return conflict;
 221 }
 222
 223 #endif
 224
 225 /***
 226  * jump_label_text_reserved - check if addr range is reserved
 227  * @start: start text addr
 228  * @end: end text addr
 229  *
 230  * checks if the text addr located between @start and @end
 231  * overlaps with any of the jump label patch addresses. Code
 232  * that wants to modify kernel text should first verify that
 233  * it does not overlap with any of the jump label addresses.
 234  *
 235  * returns 1 if there is an overlap, 0 otherwise
 236  */
 237 int jump_label_text_reserved(void *start, void *end)
 238 {
 239         struct jump_entry *iter;
 240         struct jump_entry *iter_start = __start___jump_table;
 241         struct jump_entry *iter_stop = __start___jump_table;
 242         int conflict = 0;
 243
 244         mutex_lock(&jump_label_mutex);
 245         iter = iter_start;
 246         while (iter < iter_stop) {
 247                 if (addr_conflict(iter, start, end)) {
 248                         conflict = 1;
 249                         goto out;
 250                 }
 251                 iter++;
 252         }
 253
 254         /* now check modules */
 255 #ifdef CONFIG_MODULES
 256         conflict = module_conflict(start, end);
 257 #endif
 258 out:
 259         mutex_unlock(&jump_label_mutex);
 260         return conflict;
 261 }
 262
 263 static __init int init_jump_label(void)
 264 {
 265         int ret;
 266         struct jump_entry *iter_start = __start___jump_table;
 267         struct jump_entry *iter_stop = __stop___jump_table;
 268         struct jump_entry *iter;
 269
 270         mutex_lock(&jump_label_mutex);
 271         ret = build_jump_label_hashtable(__start___jump_table,
 272                                          __stop___jump_table);
 273         iter = iter_start;
 274         while (iter < iter_stop) {
 275                 arch_jump_label_text_poke_early(iter->code);
 276                 iter++;
 277         }
 278         mutex_unlock(&jump_label_mutex);
 279         return ret;
 280 }
 281 early_initcall(init_jump_label);
 282
 283 #ifdef CONFIG_MODULES
 284
 285 static struct jump_label_module_entry *
 286 add_jump_label_module_entry(struct jump_label_entry *entry,
 287                             struct jump_entry *iter_begin,
 288                             int count, struct module *mod)
 289 {
 290         struct jump_label_module_entry *e;
 291
 292         e = kmalloc(sizeof(struct jump_label_module_entry), GFP_KERNEL);
 293         if (!e)
 294                 return ERR_PTR(-ENOMEM);
 295         e->mod = mod;
 296         e->nr_entries = count;
 297         e->table = iter_begin;
 298         hlist_add_head(&e->hlist, &entry->modules);
 299         return e;
 300 }
 301
 302 static int add_jump_label_module(struct module *mod)
 303 {
 304         struct jump_entry *iter, *iter_begin;
 305         struct jump_label_entry *entry;
 306         struct jump_label_module_entry *module_entry;
 307         int count;
 308
 309         /* if the module doesn't have jump label entries, just return */
 310         if (!mod->num_jump_entries)
 311                 return 0;
 312
 313         sort_jump_label_entries(mod->jump_entries,
 314                                 mod->jump_entries + mod->num_jump_entries);
 315         iter = mod->jump_entries;
 316         while (iter < mod->jump_entries + mod->num_jump_entries) {
 317                 entry = get_jump_label_entry(iter->key);
 318                 iter_begin = iter;
 319                 count = 0;
 320                 while ((iter < mod->jump_entries + mod->num_jump_entries) &&
 321                         (iter->key == iter_begin->key)) {
 322                                 iter++;
 323                                 count++;
 324                 }
 325                 if (!entry) {
 326                         entry = add_jump_label_entry(iter_begin->key, 0, NULL);
 327                         if (IS_ERR(entry))
 328                                 return PTR_ERR(entry);
 329                 }
 330                 module_entry = add_jump_label_module_entry(entry, iter_begin,
 331                                                            count, mod);
 332                 if (IS_ERR(module_entry))
 333                         return PTR_ERR(module_entry);
 334         }
 335         return 0;
 336 }
 337
 338 static void remove_jump_label_module(struct module *mod)
 339 {
 340         struct hlist_head *head;
 341         struct hlist_node *node, *node_next, *module_node, *module_node_next;
 342         struct jump_label_entry *e;
 343         struct jump_label_module_entry *e_module;
 344         int i;
 345
 346         /* if the module doesn't have jump label entries, just return */
 347         if (!mod->num_jump_entries)
 348                 return;
 349
 350         for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
 351                 head = &jump_label_table[i];
 352                 hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
 353                         hlist_for_each_entry_safe(e_module, module_node,
 354                                                   module_node_next,
 355                                                   &(e->modules), hlist) {
 356                                 if (e_module->mod == mod) {
 357                                         hlist_del(&e_module->hlist);
 358                                         kfree(e_module);
 359                                 }
 360                         }
 361                         if (hlist_empty(&e->modules) && (e->nr_entries == 0)) {
 362                                 hlist_del(&e->hlist);
 363                                 kfree(e);
 364                         }
 365                 }
 366         }
 367 }
 368
 369 static int
 370 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 371                          void *data)
 372 {
 373         struct module *mod = data;
 374         int ret = 0;
 375
 376         switch (val) {
 377         case MODULE_STATE_COMING:
 378                 mutex_lock(&jump_label_mutex);
 379                 ret = add_jump_label_module(mod);
 380                 if (ret)
 381                         remove_jump_label_module(mod);
 382                 mutex_unlock(&jump_label_mutex);
 383                 break;
 384         case MODULE_STATE_GOING:
 385                 mutex_lock(&jump_label_mutex);
 386                 remove_jump_label_module(mod);
 387                 mutex_unlock(&jump_label_mutex);
 388                 break;
 389         }
 390         return ret;
 391 }
 392
 393 /***
 394  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 395  * @mod: module to patch
 396  *
 397  * Allow for run-time selection of the optimal nops. Before the module
 398  * loads patch these with arch_get_jump_label_nop(), which is specified by
 399  * the arch specific jump label code.
 400  */
 401 void jump_label_apply_nops(struct module *mod)
 402 {
 403         struct jump_entry *iter;
 404
 405         /* if the module doesn't have jump label entries, just return */
 406         if (!mod->num_jump_entries)
 407                 return;
 408
 409         iter = mod->jump_entries;
 410         while (iter < mod->jump_entries + mod->num_jump_entries) {
 411                 arch_jump_label_text_poke_early(iter->code);
 412                 iter++;
 413         }
 414 }
 415
 416 struct notifier_block jump_label_module_nb = {
 417         .notifier_call = jump_label_module_notify,
 418         .priority = 0,
 419 };
 420
 421 static __init int init_jump_label_module(void)
 422 {
 423         return register_module_notifier(&jump_label_module_nb);
 424 }
 425 early_initcall(init_jump_label_module);
 426
 427 #endif /* CONFIG_MODULES */
 428
 429 #endif