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 __init int init_jump_label(void)
 181 {
 182         int ret;
 183         struct jump_entry *iter_start = __start___jump_table;
 184         struct jump_entry *iter_stop = __stop___jump_table;
 185         struct jump_entry *iter;
 186
 187         mutex_lock(&jump_label_mutex);
 188         ret = build_jump_label_hashtable(__start___jump_table,
 189                                          __stop___jump_table);
 190         iter = iter_start;
 191         while (iter < iter_stop) {
 192                 arch_jump_label_text_poke_early(iter->code);
 193                 iter++;
 194         }
 195         mutex_unlock(&jump_label_mutex);
 196         return ret;
 197 }
 198 early_initcall(init_jump_label);
 199
 200 #ifdef CONFIG_MODULES
 201
 202 static struct jump_label_module_entry *
 203 add_jump_label_module_entry(struct jump_label_entry *entry,
 204                             struct jump_entry *iter_begin,
 205                             int count, struct module *mod)
 206 {
 207         struct jump_label_module_entry *e;
 208
 209         e = kmalloc(sizeof(struct jump_label_module_entry), GFP_KERNEL);
 210         if (!e)
 211                 return ERR_PTR(-ENOMEM);
 212         e->mod = mod;
 213         e->nr_entries = count;
 214         e->table = iter_begin;
 215         hlist_add_head(&e->hlist, &entry->modules);
 216         return e;
 217 }
 218
 219 static int add_jump_label_module(struct module *mod)
 220 {
 221         struct jump_entry *iter, *iter_begin;
 222         struct jump_label_entry *entry;
 223         struct jump_label_module_entry *module_entry;
 224         int count;
 225
 226         /* if the module doesn't have jump label entries, just return */
 227         if (!mod->num_jump_entries)
 228                 return 0;
 229
 230         sort_jump_label_entries(mod->jump_entries,
 231                                 mod->jump_entries + mod->num_jump_entries);
 232         iter = mod->jump_entries;
 233         while (iter < mod->jump_entries + mod->num_jump_entries) {
 234                 entry = get_jump_label_entry(iter->key);
 235                 iter_begin = iter;
 236                 count = 0;
 237                 while ((iter < mod->jump_entries + mod->num_jump_entries) &&
 238                         (iter->key == iter_begin->key)) {
 239                                 iter++;
 240                                 count++;
 241                 }
 242                 if (!entry) {
 243                         entry = add_jump_label_entry(iter_begin->key, 0, NULL);
 244                         if (IS_ERR(entry))
 245                                 return PTR_ERR(entry);
 246                 }
 247                 module_entry = add_jump_label_module_entry(entry, iter_begin,
 248                                                            count, mod);
 249                 if (IS_ERR(module_entry))
 250                         return PTR_ERR(module_entry);
 251         }
 252         return 0;
 253 }
 254
 255 static void remove_jump_label_module(struct module *mod)
 256 {
 257         struct hlist_head *head;
 258         struct hlist_node *node, *node_next, *module_node, *module_node_next;
 259         struct jump_label_entry *e;
 260         struct jump_label_module_entry *e_module;
 261         int i;
 262
 263         /* if the module doesn't have jump label entries, just return */
 264         if (!mod->num_jump_entries)
 265                 return;
 266
 267         for (i = 0; i < JUMP_LABEL_TABLE_SIZE; i++) {
 268                 head = &jump_label_table[i];
 269                 hlist_for_each_entry_safe(e, node, node_next, head, hlist) {
 270                         hlist_for_each_entry_safe(e_module, module_node,
 271                                                   module_node_next,
 272                                                   &(e->modules), hlist) {
 273                                 if (e_module->mod == mod) {
 274                                         hlist_del(&e_module->hlist);
 275                                         kfree(e_module);
 276                                 }
 277                         }
 278                         if (hlist_empty(&e->modules) && (e->nr_entries == 0)) {
 279                                 hlist_del(&e->hlist);
 280                                 kfree(e);
 281                         }
 282                 }
 283         }
 284 }
 285
 286 static int
 287 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 288                          void *data)
 289 {
 290         struct module *mod = data;
 291         int ret = 0;
 292
 293         switch (val) {
 294         case MODULE_STATE_COMING:
 295                 mutex_lock(&jump_label_mutex);
 296                 ret = add_jump_label_module(mod);
 297                 if (ret)
 298                         remove_jump_label_module(mod);
 299                 mutex_unlock(&jump_label_mutex);
 300                 break;
 301         case MODULE_STATE_GOING:
 302                 mutex_lock(&jump_label_mutex);
 303                 remove_jump_label_module(mod);
 304                 mutex_unlock(&jump_label_mutex);
 305                 break;
 306         }
 307         return ret;
 308 }
 309
 310 /***
 311  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 312  * @mod: module to patch
 313  *
 314  * Allow for run-time selection of the optimal nops. Before the module
 315  * loads patch these with arch_get_jump_label_nop(), which is specified by
 316  * the arch specific jump label code.
 317  */
 318 void jump_label_apply_nops(struct module *mod)
 319 {
 320         struct jump_entry *iter;
 321
 322         /* if the module doesn't have jump label entries, just return */
 323         if (!mod->num_jump_entries)
 324                 return;
 325
 326         iter = mod->jump_entries;
 327         while (iter < mod->jump_entries + mod->num_jump_entries) {
 328                 arch_jump_label_text_poke_early(iter->code);
 329                 iter++;
 330         }
 331 }
 332
 333 struct notifier_block jump_label_module_nb = {
 334         .notifier_call = jump_label_module_notify,
 335         .priority = 0,
 336 };
 337
 338 static __init int init_jump_label_module(void)
 339 {
 340         return register_module_notifier(&jump_label_module_nb);
 341 }
 342 early_initcall(init_jump_label_module);
 343
 344 #endif /* CONFIG_MODULES */
 345
 346 #endif