linux/kernel/jump_label.c
<<
>>
Prefs
   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 */
  20static DEFINE_MUTEX(jump_label_mutex);
  21
  22void jump_label_lock(void)
  23{
  24        mutex_lock(&jump_label_mutex);
  25}
  26
  27void jump_label_unlock(void)
  28{
  29        mutex_unlock(&jump_label_mutex);
  30}
  31
  32static 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
  46static void
  47jump_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
  56static void jump_label_update(struct static_key *key, int enable);
  57
  58void 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}
  73EXPORT_SYMBOL_GPL(static_key_slow_inc);
  74
  75static 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
  96static 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
 103void static_key_slow_dec(struct static_key *key)
 104{
 105        __static_key_slow_dec(key, 0, NULL);
 106}
 107EXPORT_SYMBOL_GPL(static_key_slow_dec);
 108
 109void static_key_slow_dec_deferred(struct static_key_deferred *key)
 110{
 111        __static_key_slow_dec(&key->key, key->timeout, &key->work);
 112}
 113EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 114
 115void 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
 122static 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
 131static 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 */
 152void __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
 158static 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
 175static 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
 186void __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
 218struct static_key_mod {
 219        struct static_key_mod *next;
 220        struct jump_entry *entries;
 221        struct module *mod;
 222};
 223
 224static 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
 239static 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 */
 261void 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
 276static 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
 321static 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
 353static 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
 365static int
 366jump_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
 395struct notifier_block jump_label_module_nb = {
 396        .notifier_call = jump_label_module_notify,
 397        .priority = 1, /* higher than tracepoints */
 398};
 399
 400static __init int jump_label_init_module(void)
 401{
 402        return register_module_notifier(&jump_label_module_nb);
 403}
 404early_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 */
 421int 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
 435static 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
 454
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.