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/static_key.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 static int jump_label_cmp(const void *a, const void *b)
  33 {
  34         const struct jump_entry *jea = a;
  35         const struct jump_entry *jeb = b;
  36
  37         if (jea->key < jeb->key)
  38                 return -1;
  39
  40         if (jea->key > jeb->key)
  41                 return 1;
  42
  43         return 0;
  44 }
  45
  46 static void
  47 jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
  48 {
  49         unsigned long size;
  50
  51         size = (((unsigned long)stop - (unsigned long)start)
  52                                         / sizeof(struct jump_entry));
  53         sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  54 }
  55
  56 static void jump_label_update(struct static_key *key, int enable);
  57
  58 void static_key_slow_inc(struct static_key *key)
  59 {
  60         if (atomic_inc_not_zero(&key->enabled))
  61                 return;
  62
  63         jump_label_lock();
  64         if (atomic_read(&key->enabled) == 0) {
  65                 if (!jump_label_get_branch_default(key))
  66                         jump_label_update(key, JUMP_LABEL_ENABLE);
  67                 else
  68                         jump_label_update(key, JUMP_LABEL_DISABLE);
  69         }
  70         atomic_inc(&key->enabled);
  71         jump_label_unlock();
  72 }
  73 EXPORT_SYMBOL_GPL(static_key_slow_inc);
  74
  75 static void __static_key_slow_dec(struct static_key *key,
  76                 unsigned long rate_limit, struct delayed_work *work)
  77 {
  78         if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
  79                 WARN(atomic_read(&key->enabled) < 0,
  80                      "jump label: negative count!\n");
  81                 return;
  82         }
  83
  84         if (rate_limit) {
  85                 atomic_inc(&key->enabled);
  86                 schedule_delayed_work(work, rate_limit);
  87         } else {
  88                 if (!jump_label_get_branch_default(key))
  89                         jump_label_update(key, JUMP_LABEL_DISABLE);
  90                 else
  91                         jump_label_update(key, JUMP_LABEL_ENABLE);
  92         }
  93         jump_label_unlock();
  94 }
  95
  96 static void jump_label_update_timeout(struct work_struct *work)
  97 {
  98         struct static_key_deferred *key =
  99                 container_of(work, struct static_key_deferred, work.work);
 100         __static_key_slow_dec(&key->key, 0, NULL);
 101 }
 102
 103 void static_key_slow_dec(struct static_key *key)
 104 {
 105         __static_key_slow_dec(key, 0, NULL);
 106 }
 107 EXPORT_SYMBOL_GPL(static_key_slow_dec);
 108
 109 void static_key_slow_dec_deferred(struct static_key_deferred *key)
 110 {
 111         __static_key_slow_dec(&key->key, key->timeout, &key->work);
 112 }
 113 EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 114
 115 void jump_label_rate_limit(struct static_key_deferred *key,
 116                 unsigned long rl)
 117 {
 118         key->timeout = rl;
 119         INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 120 }
 121
 122 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 123 {
 124         if (entry->code <= (unsigned long)end &&
 125                 entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 126                 return 1;
 127
 128         return 0;
 129 }
 130
 131 static int __jump_label_text_reserved(struct jump_entry *iter_start,
 132                 struct jump_entry *iter_stop, void *start, void *end)
 133 {
 134         struct jump_entry *iter;
 135
 136         iter = iter_start;
 137         while (iter < iter_stop) {
 138                 if (addr_conflict(iter, start, end))
 139                         return 1;
 140                 iter++;
 141         }
 142
 143         return 0;
 144 }
 145
 146 /*
 147  * Update code which is definitely not currently executing.
 148  * Architectures which need heavyweight synchronization to modify
 149  * running code can override this to make the non-live update case
 150  * cheaper.
 151  */
 152 void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 153                                             enum jump_label_type type)
 154 {
 155         arch_jump_label_transform(entry, type);
 156 }
 157
 158 static void __jump_label_update(struct static_key *key,
 159                                 struct jump_entry *entry,
 160                                 struct jump_entry *stop, int enable)
 161 {
 162         for (; (entry < stop) &&
 163               (entry->key == (jump_label_t)(unsigned long)key);
 164               entry++) {
 165                 /*
 166                  * entry->code set to 0 invalidates module init text sections
 167                  * kernel_text_address() verifies we are not in core kernel
 168                  * init code, see jump_label_invalidate_module_init().
 169                  */
 170                 if (entry->code && kernel_text_address(entry->code))
 171                         arch_jump_label_transform(entry, enable);
 172         }
 173 }
 174
 175 static enum jump_label_type jump_label_type(struct static_key *key)
 176 {
 177         bool true_branch = jump_label_get_branch_default(key);
 178         bool state = static_key_enabled(key);
 179
 180         if ((!true_branch && state) || (true_branch && !state))
 181                 return JUMP_LABEL_ENABLE;
 182
 183         return JUMP_LABEL_DISABLE;
 184 }
 185
 186 void __init jump_label_init(void)
 187 {
 188         struct jump_entry *iter_start = __start___jump_table;
 189         struct jump_entry *iter_stop = __stop___jump_table;
 190         struct static_key *key = NULL;
 191         struct jump_entry *iter;
 192
 193         jump_label_lock();
 194         jump_label_sort_entries(iter_start, iter_stop);
 195
 196         for (iter = iter_start; iter < iter_stop; iter++) {
 197                 struct static_key *iterk;
 198
 199                 iterk = (struct static_key *)(unsigned long)iter->key;
 200                 arch_jump_label_transform_static(iter, jump_label_type(iterk));
 201                 if (iterk == key)
 202                         continue;
 203
 204                 key = iterk;
 205                 /*
 206                  * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 207                  */
 208                 *((unsigned long *)&key->entries) += (unsigned long)iter;
 209 #ifdef CONFIG_MODULES
 210                 key->next = NULL;
 211 #endif
 212         }
 213         jump_label_unlock();
 214 }
 215
 216 #ifdef CONFIG_MODULES
 217
 218 struct static_key_mod {
 219         struct static_key_mod *next;
 220         struct jump_entry *entries;
 221         struct module *mod;
 222 };
 223
 224 static int __jump_label_mod_text_reserved(void *start, void *end)
 225 {
 226         struct module *mod;
 227
 228         mod = __module_text_address((unsigned long)start);
 229         if (!mod)
 230                 return 0;
 231
 232         WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 233
 234         return __jump_label_text_reserved(mod->jump_entries,
 235                                 mod->jump_entries + mod->num_jump_entries,
 236                                 start, end);
 237 }
 238
 239 static void __jump_label_mod_update(struct static_key *key, int enable)
 240 {
 241         struct static_key_mod *mod = key->next;
 242
 243         while (mod) {
 244                 struct module *m = mod->mod;
 245
 246                 __jump_label_update(key, mod->entries,
 247                                     m->jump_entries + m->num_jump_entries,
 248                                     enable);
 249                 mod = mod->next;
 250         }
 251 }
 252
 253 /***
 254  * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 255  * @mod: module to patch
 256  *
 257  * Allow for run-time selection of the optimal nops. Before the module
 258  * loads patch these with arch_get_jump_label_nop(), which is specified by
 259  * the arch specific jump label code.
 260  */
 261 void jump_label_apply_nops(struct module *mod)
 262 {
 263         struct jump_entry *iter_start = mod->jump_entries;
 264         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 265         struct jump_entry *iter;
 266
 267         /* if the module doesn't have jump label entries, just return */
 268         if (iter_start == iter_stop)
 269                 return;
 270
 271         for (iter = iter_start; iter < iter_stop; iter++) {
 272                 arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
 273         }
 274 }
 275
 276 static int jump_label_add_module(struct module *mod)
 277 {
 278         struct jump_entry *iter_start = mod->jump_entries;
 279         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 280         struct jump_entry *iter;
 281         struct static_key *key = NULL;
 282         struct static_key_mod *jlm;
 283
 284         /* if the module doesn't have jump label entries, just return */
 285         if (iter_start == iter_stop)
 286                 return 0;
 287
 288         jump_label_sort_entries(iter_start, iter_stop);
 289
 290         for (iter = iter_start; iter < iter_stop; iter++) {
 291                 struct static_key *iterk;
 292
 293                 iterk = (struct static_key *)(unsigned long)iter->key;
 294                 if (iterk == key)
 295                         continue;
 296
 297                 key = iterk;
 298                 if (__module_address(iter->key) == mod) {
 299                         /*
 300                          * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 301                          */
 302                         *((unsigned long *)&key->entries) += (unsigned long)iter;
 303                         key->next = NULL;
 304                         continue;
 305                 }
 306                 jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 307                 if (!jlm)
 308                         return -ENOMEM;
 309                 jlm->mod = mod;
 310                 jlm->entries = iter;
 311                 jlm->next = key->next;
 312                 key->next = jlm;
 313
 314                 if (jump_label_type(key) == JUMP_LABEL_ENABLE)
 315                         __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
 316         }
 317
 318         return 0;
 319 }
 320
 321 static void jump_label_del_module(struct module *mod)
 322 {
 323         struct jump_entry *iter_start = mod->jump_entries;
 324         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 325         struct jump_entry *iter;
 326         struct static_key *key = NULL;
 327         struct static_key_mod *jlm, **prev;
 328
 329         for (iter = iter_start; iter < iter_stop; iter++) {
 330                 if (iter->key == (jump_label_t)(unsigned long)key)
 331                         continue;
 332
 333                 key = (struct static_key *)(unsigned long)iter->key;
 334
 335                 if (__module_address(iter->key) == mod)
 336                         continue;
 337
 338                 prev = &key->next;
 339                 jlm = key->next;
 340
 341                 while (jlm && jlm->mod != mod) {
 342                         prev = &jlm->next;
 343                         jlm = jlm->next;
 344                 }
 345
 346                 if (jlm) {
 347                         *prev = jlm->next;
 348                         kfree(jlm);
 349                 }
 350         }
 351 }
 352
 353 static void jump_label_invalidate_module_init(struct module *mod)
 354 {
 355         struct jump_entry *iter_start = mod->jump_entries;
 356         struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 357         struct jump_entry *iter;
 358
 359         for (iter = iter_start; iter < iter_stop; iter++) {
 360                 if (within_module_init(iter->code, mod))
 361                         iter->code = 0;
 362         }
 363 }
 364
 365 static int
 366 jump_label_module_notify(struct notifier_block *self, unsigned long val,
 367                          void *data)
 368 {
 369         struct module *mod = data;
 370         int ret = 0;
 371
 372         switch (val) {
 373         case MODULE_STATE_COMING:
 374                 jump_label_lock();
 375                 ret = jump_label_add_module(mod);
 376                 if (ret)
 377                         jump_label_del_module(mod);
 378                 jump_label_unlock();
 379                 break;
 380         case MODULE_STATE_GOING:
 381                 jump_label_lock();
 382                 jump_label_del_module(mod);
 383                 jump_label_unlock();
 384                 break;
 385         case MODULE_STATE_LIVE:
 386                 jump_label_lock();
 387                 jump_label_invalidate_module_init(mod);
 388                 jump_label_unlock();
 389                 break;
 390         }
 391
 392         return notifier_from_errno(ret);
 393 }
 394
 395 struct notifier_block jump_label_module_nb = {
 396         .notifier_call = jump_label_module_notify,
 397         .priority = 1, /* higher than tracepoints */
 398 };
 399
 400 static __init int jump_label_init_module(void)
 401 {
 402         return register_module_notifier(&jump_label_module_nb);
 403 }
 404 early_initcall(jump_label_init_module);
 405
 406 #endif /* CONFIG_MODULES */
 407
 408 /***
 409  * jump_label_text_reserved - check if addr range is reserved
 410  * @start: start text addr
 411  * @end: end text addr
 412  *
 413  * checks if the text addr located between @start and @end
 414  * overlaps with any of the jump label patch addresses. Code
 415  * that wants to modify kernel text should first verify that
 416  * it does not overlap with any of the jump label addresses.
 417  * Caller must hold jump_label_mutex.
 418  *
 419  * returns 1 if there is an overlap, 0 otherwise
 420  */
 421 int jump_label_text_reserved(void *start, void *end)
 422 {
 423         int ret = __jump_label_text_reserved(__start___jump_table,
 424                         __stop___jump_table, start, end);
 425
 426         if (ret)
 427                 return ret;
 428
 429 #ifdef CONFIG_MODULES
 430         ret = __jump_label_mod_text_reserved(start, end);
 431 #endif
 432         return ret;
 433 }
 434
 435 static void jump_label_update(struct static_key *key, int enable)
 436 {
 437         struct jump_entry *stop = __stop___jump_table;
 438         struct jump_entry *entry = jump_label_get_entries(key);
 439
 440 #ifdef CONFIG_MODULES
 441         struct module *mod = __module_address((unsigned long)key);
 442
 443         __jump_label_mod_update(key, enable);
 444
 445         if (mod)
 446                 stop = mod->jump_entries + mod->num_jump_entries;
 447 #endif
 448         /* if there are no users, entry can be NULL */
 449         if (entry)
 450                 __jump_label_update(key, entry, stop, enable);
 451 }
 452
 453 #endif