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_read(&key->enabled) == 0)
  70                 jump_label_update(key, JUMP_LABEL_ENABLE);
  71         atomic_inc(&key->enabled);
  72         jump_label_unlock();
  73 }
  74
  75 void jump_label_dec(struct jump_label_key *key)
  76 {
  77         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
  78                 return;
  79
  80         jump_label_update(key, JUMP_LABEL_DISABLE);
  81         jump_label_unlock();
  82 }
  83
  84 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
  85 {
  86         if (entry->code <= (unsigned long)end &&
  87                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
  88                 return 1;
  89
  90         return 0;
  91 }
  92
  93 static int __jump_label_text_reserved(struct jump_entry *iter_start,
  94                 struct jump_entry *iter_stop, void *start, void *end)
  95 {
  96         struct jump_entry *iter;
  97
  98         iter = iter_start;
  99         while (iter < iter_stop) {
 100                 if (addr_conflict(iter, start, end))
 101                         return 1;
 102                 iter++;
 103         }
 104
 105         return 0;
 106 }
 107
 108 static void __jump_label_update(struct jump_label_key *key,
 109                                 struct jump_entry *entry,
 110                                 struct jump_entry *stop, int enable)
 111 {
 112         for (; (entry < stop) &&
 113               (entry->key == (jump_label_t)(unsigned long)key);
 114               entry++) {
 115                 /*
 116                  * entry->code set to 0 invalidates module init text sections
 117                  * kernel_text_address() verifies we are not in core kernel
 118                  * init code, see jump_label_invalidate_module_init().
 119                  */
 120                 if (entry->code && kernel_text_address(entry->code))
 121                         arch_jump_label_transform(entry, enable);
 122         }
 123 }
 124
 125 /*
 126  * Not all archs need this.
 127  */
 128 void __weak arch_jump_label_text_poke_early(jump_label_t addr)
 129 {
 130 }
 131
 132 static __init int jump_label_init(void)
 133 {
 134         struct jump_entry *iter_start = __start___jump_table;
 135         struct jump_entry *iter_stop = __stop___jump_table;
 136         struct jump_label_key *key = NULL;
 137         struct jump_entry *iter;
 138
 139         jump_label_lock();
 140         jump_label_sort_entries(iter_start, iter_stop);
 141
 142         for (iter = iter_start; iter < iter_stop; iter++) {
 143                 arch_jump_label_text_poke_early(iter->code);
 144                 if (iter->key == (jump_label_t)(unsigned long)key)
 145                         continue;
 146
 147                 key = (struct jump_label_key *)(unsigned long)iter->key;
 148                 atomic_set(&key->enabled, 0);
 149                 key->entries = iter;
 150 #ifdef CONFIG_MODULES
 151                 key->next = NULL;
 152 #endif
 153         }
 154         jump_label_unlock();
 155
 156         return 0;
 157 }
 158 early_initcall(jump_label_init);
 159
 160 #ifdef CONFIG_MODULES
 161
 162 struct jump_label_mod {
 163         struct jump_label_mod *next;
 164         struct jump_entry *entries;
 165         struct module *mod;
 166 };
 167
 168 static int __jump_label_mod_text_reserved(void *start, void *end)
 169 {
 170         struct module *mod;
 171
 172         mod = __module_text_address((unsigned long)start);
 173         if (!mod)
 174                 return 0;
 175
 176         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 177
 178         return __jump_label_text_reserved(mod->jump_entries,
 179                                 mod->jump_entries + mod->num_jump_entries,
 180                                 start, end);
 181 }
 182
 183 static void __jump_label_mod_update(struct jump_label_key *key, int enable)
 184 {
 185         struct jump_label_mod *mod = key->next;
 186
 187         while (mod) {
 188                 struct module *m = mod->mod;
 189
 190                 __jump_label_update(key, mod->entries,
 191                                     m->jump_entries + m->num_jump_entries,
 192                                     enable);
 193                 mod = mod->next;
 194         }
 195 }
 196
 197 /***
 198  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 199  * @mod: module to patch
 200  *
 201  * Allow for run-time selection of the optimal nops. Before the module
 202  * loads patch these with arch_get_jump_label_nop(), which is specified by
 203  * the arch specific jump label code.
 204  */
 205 void jump_label_apply_nops(struct module *mod)
 206 {
 207         struct jump_entry *iter_start = mod->jump_entries;
 208         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 209         struct jump_entry *iter;
 210
 211         /* if the module doesn't have jump label entries, just return */
 212         if (iter_start == iter_stop)
 213                 return;
 214
 215         for (iter = iter_start; iter < iter_stop; iter++)
 216                 arch_jump_label_text_poke_early(iter->code);
 217 }
 218
 219 static int jump_label_add_module(struct module *mod)
 220 {
 221         struct jump_entry *iter_start = mod->jump_entries;
 222         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 223         struct jump_entry *iter;
 224         struct jump_label_key *key = NULL;
 225         struct jump_label_mod *jlm;
 226
 227         /* if the module doesn't have jump label entries, just return */
 228         if (iter_start == iter_stop)
 229                 return 0;
 230
 231         jump_label_sort_entries(iter_start, iter_stop);
 232
 233         for (iter = iter_start; iter < iter_stop; iter++) {
 234                 if (iter->key == (jump_label_t)(unsigned long)key)
 235                         continue;
 236
 237                 key = (struct jump_label_key *)(unsigned long)iter->key;
 238
 239                 if (__module_address(iter->key) == mod) {
 240                         atomic_set(&key->enabled, 0);
 241                         key->entries = iter;
 242                         key->next = NULL;
 243                         continue;
 244                 }
 245
 246                 jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
 247                 if (!jlm)
 248                         return -ENOMEM;
 249
 250                 jlm->mod = mod;
 251                 jlm->entries = iter;
 252                 jlm->next = key->next;
 253                 key->next = jlm;
 254
 255                 if (jump_label_enabled(key))
 256                         __jump_label_update(key, iter, iter_stop,
 257                                             JUMP_LABEL_ENABLE);
 258         }
 259
 260         return 0;
 261 }
 262
 263 static void jump_label_del_module(struct module *mod)
 264 {
 265         struct jump_entry *iter_start = mod->jump_entries;
 266         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 267         struct jump_entry *iter;
 268         struct jump_label_key *key = NULL;
 269         struct jump_label_mod *jlm, **prev;
 270
 271         for (iter = iter_start; iter < iter_stop; iter++) {
 272                 if (iter->key == (jump_label_t)(unsigned long)key)
 273                         continue;
 274
 275                 key = (struct jump_label_key *)(unsigned long)iter->key;
 276
 277                 if (__module_address(iter->key) == mod)
 278                         continue;
 279
 280                 prev = &key->next;
 281                 jlm = key->next;
 282
 283                 while (jlm && jlm->mod != mod) {
 284                         prev = &jlm->next;
 285                         jlm = jlm->next;
 286                 }
 287
 288                 if (jlm) {
 289                         *prev = jlm->next;
 290                         kfree(jlm);
 291                 }
 292         }
 293 }
 294
 295 static void jump_label_invalidate_module_init(struct module *mod)
 296 {
 297         struct jump_entry *iter_start = mod->jump_entries;
 298         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 299         struct jump_entry *iter;
 300
 301         for (iter = iter_start; iter < iter_stop; iter++) {
 302                 if (within_module_init(iter->code, mod))
 303                         iter->code = 0;
 304         }
 305 }
 306
 307 static int
 308 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 309                          void *data)
 310 {
 311         struct module *mod = data;
 312         int ret = 0;
 313
 314         switch (val) {
 315         case MODULE_STATE_COMING:
 316                 jump_label_lock();
 317                 ret = jump_label_add_module(mod);
 318                 if (ret)
 319                         jump_label_del_module(mod);
 320                 jump_label_unlock();
 321                 break;
 322         case MODULE_STATE_GOING:
 323                 jump_label_lock();
 324                 jump_label_del_module(mod);
 325                 jump_label_unlock();
 326                 break;
 327         case MODULE_STATE_LIVE:
 328                 jump_label_lock();
 329                 jump_label_invalidate_module_init(mod);
 330                 jump_label_unlock();
 331                 break;
 332         }
 333
 334         return notifier_from_errno(ret);
 335 }
 336
 337 struct notifier_block jump_label_module_nb = {
 338         .notifier_call = jump_label_module_notify,
 339         .priority = 1, /* higher than tracepoints */
 340 };
 341
 342 static __init int jump_label_init_module(void)
 343 {
 344         return register_module_notifier(&jump_label_module_nb);
 345 }
 346 early_initcall(jump_label_init_module);
 347
 348 #endif /* CONFIG_MODULES */
 349
 350 /***
 351  * jump_label_text_reserved - check if addr range is reserved
 352  * @start: start text addr
 353  * @end: end text addr
 354  *
 355  * checks if the text addr located between @start and @end
 356  * overlaps with any of the jump label patch addresses. Code
 357  * that wants to modify kernel text should first verify that
 358  * it does not overlap with any of the jump label addresses.
 359  * Caller must hold jump_label_mutex.
 360  *
 361  * returns 1 if there is an overlap, 0 otherwise
 362  */
 363 int jump_label_text_reserved(void *start, void *end)
 364 {
 365         int ret = __jump_label_text_reserved(__start___jump_table,
 366                         __stop___jump_table, start, end);
 367
 368         if (ret)
 369                 return ret;
 370
 371 #ifdef CONFIG_MODULES
 372         ret = __jump_label_mod_text_reserved(start, end);
 373 #endif
 374         return ret;
 375 }
 376
 377 static void jump_label_update(struct jump_label_key *key, int enable)
 378 {
 379         struct jump_entry *entry = key->entries, *stop = __stop___jump_table;
 380
 381 #ifdef CONFIG_MODULES
 382         struct module *mod = __module_address((jump_label_t)key);
 383
 384         __jump_label_mod_update(key, enable);
 385
 386         if (mod)
 387                 stop = mod->jump_entries + mod->num_jump_entries;
 388 #endif
 389         /* if there are no users, entry can be NULL */
 390         if (entry)
 391                 __jump_label_update(key, entry, stop, enable);
 392 }
 393
 394 #endif