linux/kernel/jump_label.c
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   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#include <linux/jump_label_ratelimit.h>
  17
  18#ifdef HAVE_JUMP_LABEL
  19
  20/* mutex to protect coming/going of the the jump_label table */
  21static DEFINE_MUTEX(jump_label_mutex);
  22
  23void jump_label_lock(void)
  24{
  25        mutex_lock(&jump_label_mutex);
  26}
  27
  28void jump_label_unlock(void)
  29{
  30        mutex_unlock(&jump_label_mutex);
  31}
  32
  33static int jump_label_cmp(const void *a, const void *b)
  34{
  35        const struct jump_entry *jea = a;
  36        const struct jump_entry *jeb = b;
  37
  38        if (jea->key < jeb->key)
  39                return -1;
  40
  41        if (jea->key > jeb->key)
  42                return 1;
  43
  44        return 0;
  45}
  46
  47static void
  48jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
  49{
  50        unsigned long size;
  51
  52        size = (((unsigned long)stop - (unsigned long)start)
  53                                        / sizeof(struct jump_entry));
  54        sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
  55}
  56
  57static void jump_label_update(struct static_key *key);
  58
  59void static_key_slow_inc(struct static_key *key)
  60{
  61        STATIC_KEY_CHECK_USE();
  62        if (atomic_inc_not_zero(&key->enabled))
  63                return;
  64
  65        jump_label_lock();
  66        if (atomic_inc_return(&key->enabled) == 1)
  67                jump_label_update(key);
  68        jump_label_unlock();
  69}
  70EXPORT_SYMBOL_GPL(static_key_slow_inc);
  71
  72static void __static_key_slow_dec(struct static_key *key,
  73                unsigned long rate_limit, struct delayed_work *work)
  74{
  75        if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
  76                WARN(atomic_read(&key->enabled) < 0,
  77                     "jump label: negative count!\n");
  78                return;
  79        }
  80
  81        if (rate_limit) {
  82                atomic_inc(&key->enabled);
  83                schedule_delayed_work(work, rate_limit);
  84        } else {
  85                jump_label_update(key);
  86        }
  87        jump_label_unlock();
  88}
  89
  90static void jump_label_update_timeout(struct work_struct *work)
  91{
  92        struct static_key_deferred *key =
  93                container_of(work, struct static_key_deferred, work.work);
  94        __static_key_slow_dec(&key->key, 0, NULL);
  95}
  96
  97void static_key_slow_dec(struct static_key *key)
  98{
  99        STATIC_KEY_CHECK_USE();
 100        __static_key_slow_dec(key, 0, NULL);
 101}
 102EXPORT_SYMBOL_GPL(static_key_slow_dec);
 103
 104void static_key_slow_dec_deferred(struct static_key_deferred *key)
 105{
 106        STATIC_KEY_CHECK_USE();
 107        __static_key_slow_dec(&key->key, key->timeout, &key->work);
 108}
 109EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);
 110
 111void jump_label_rate_limit(struct static_key_deferred *key,
 112                unsigned long rl)
 113{
 114        STATIC_KEY_CHECK_USE();
 115        key->timeout = rl;
 116        INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
 117}
 118EXPORT_SYMBOL_GPL(jump_label_rate_limit);
 119
 120static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 121{
 122        if (entry->code <= (unsigned long)end &&
 123                entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
 124                return 1;
 125
 126        return 0;
 127}
 128
 129static int __jump_label_text_reserved(struct jump_entry *iter_start,
 130                struct jump_entry *iter_stop, void *start, void *end)
 131{
 132        struct jump_entry *iter;
 133
 134        iter = iter_start;
 135        while (iter < iter_stop) {
 136                if (addr_conflict(iter, start, end))
 137                        return 1;
 138                iter++;
 139        }
 140
 141        return 0;
 142}
 143
 144/*
 145 * Update code which is definitely not currently executing.
 146 * Architectures which need heavyweight synchronization to modify
 147 * running code can override this to make the non-live update case
 148 * cheaper.
 149 */
 150void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
 151                                            enum jump_label_type type)
 152{
 153        arch_jump_label_transform(entry, type);
 154}
 155
 156static inline struct jump_entry *static_key_entries(struct static_key *key)
 157{
 158        return (struct jump_entry *)((unsigned long)key->entries & ~JUMP_TYPE_MASK);
 159}
 160
 161static inline bool static_key_type(struct static_key *key)
 162{
 163        return (unsigned long)key->entries & JUMP_TYPE_MASK;
 164}
 165
 166static inline struct static_key *jump_entry_key(struct jump_entry *entry)
 167{
 168        return (struct static_key *)((unsigned long)entry->key & ~1UL);
 169}
 170
 171static bool jump_entry_branch(struct jump_entry *entry)
 172{
 173        return (unsigned long)entry->key & 1UL;
 174}
 175
 176static enum jump_label_type jump_label_type(struct jump_entry *entry)
 177{
 178        struct static_key *key = jump_entry_key(entry);
 179        bool enabled = static_key_enabled(key);
 180        bool branch = jump_entry_branch(entry);
 181
 182        /* See the comment in linux/jump_label.h */
 183        return enabled ^ branch;
 184}
 185
 186static void __jump_label_update(struct static_key *key,
 187                                struct jump_entry *entry,
 188                                struct jump_entry *stop)
 189{
 190        for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
 191                /*
 192                 * entry->code set to 0 invalidates module init text sections
 193                 * kernel_text_address() verifies we are not in core kernel
 194                 * init code, see jump_label_invalidate_module_init().
 195                 */
 196                if (entry->code && kernel_text_address(entry->code))
 197                        arch_jump_label_transform(entry, jump_label_type(entry));
 198        }
 199}
 200
 201void __init jump_label_init(void)
 202{
 203        struct jump_entry *iter_start = __start___jump_table;
 204        struct jump_entry *iter_stop = __stop___jump_table;
 205        struct static_key *key = NULL;
 206        struct jump_entry *iter;
 207
 208        jump_label_lock();
 209        jump_label_sort_entries(iter_start, iter_stop);
 210
 211        for (iter = iter_start; iter < iter_stop; iter++) {
 212                struct static_key *iterk;
 213
 214                /* rewrite NOPs */
 215                if (jump_label_type(iter) == JUMP_LABEL_NOP)
 216                        arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 217
 218                iterk = jump_entry_key(iter);
 219                if (iterk == key)
 220                        continue;
 221
 222                key = iterk;
 223                /*
 224                 * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 225                 */
 226                *((unsigned long *)&key->entries) += (unsigned long)iter;
 227#ifdef CONFIG_MODULES
 228                key->next = NULL;
 229#endif
 230        }
 231        static_key_initialized = true;
 232        jump_label_unlock();
 233}
 234
 235#ifdef CONFIG_MODULES
 236
 237static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
 238{
 239        struct static_key *key = jump_entry_key(entry);
 240        bool type = static_key_type(key);
 241        bool branch = jump_entry_branch(entry);
 242
 243        /* See the comment in linux/jump_label.h */
 244        return type ^ branch;
 245}
 246
 247struct static_key_mod {
 248        struct static_key_mod *next;
 249        struct jump_entry *entries;
 250        struct module *mod;
 251};
 252
 253static int __jump_label_mod_text_reserved(void *start, void *end)
 254{
 255        struct module *mod;
 256
 257        mod = __module_text_address((unsigned long)start);
 258        if (!mod)
 259                return 0;
 260
 261        WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
 262
 263        return __jump_label_text_reserved(mod->jump_entries,
 264                                mod->jump_entries + mod->num_jump_entries,
 265                                start, end);
 266}
 267
 268static void __jump_label_mod_update(struct static_key *key)
 269{
 270        struct static_key_mod *mod;
 271
 272        for (mod = key->next; mod; mod = mod->next) {
 273                struct module *m = mod->mod;
 274
 275                __jump_label_update(key, mod->entries,
 276                                    m->jump_entries + m->num_jump_entries);
 277        }
 278}
 279
 280/***
 281 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 282 * @mod: module to patch
 283 *
 284 * Allow for run-time selection of the optimal nops. Before the module
 285 * loads patch these with arch_get_jump_label_nop(), which is specified by
 286 * the arch specific jump label code.
 287 */
 288void jump_label_apply_nops(struct module *mod)
 289{
 290        struct jump_entry *iter_start = mod->jump_entries;
 291        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 292        struct jump_entry *iter;
 293
 294        /* if the module doesn't have jump label entries, just return */
 295        if (iter_start == iter_stop)
 296                return;
 297
 298        for (iter = iter_start; iter < iter_stop; iter++) {
 299                /* Only write NOPs for arch_branch_static(). */
 300                if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
 301                        arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
 302        }
 303}
 304
 305static int jump_label_add_module(struct module *mod)
 306{
 307        struct jump_entry *iter_start = mod->jump_entries;
 308        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 309        struct jump_entry *iter;
 310        struct static_key *key = NULL;
 311        struct static_key_mod *jlm;
 312
 313        /* if the module doesn't have jump label entries, just return */
 314        if (iter_start == iter_stop)
 315                return 0;
 316
 317        jump_label_sort_entries(iter_start, iter_stop);
 318
 319        for (iter = iter_start; iter < iter_stop; iter++) {
 320                struct static_key *iterk;
 321
 322                iterk = jump_entry_key(iter);
 323                if (iterk == key)
 324                        continue;
 325
 326                key = iterk;
 327                if (within_module(iter->key, mod)) {
 328                        /*
 329                         * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
 330                         */
 331                        *((unsigned long *)&key->entries) += (unsigned long)iter;
 332                        key->next = NULL;
 333                        continue;
 334                }
 335                jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
 336                if (!jlm)
 337                        return -ENOMEM;
 338                jlm->mod = mod;
 339                jlm->entries = iter;
 340                jlm->next = key->next;
 341                key->next = jlm;
 342
 343                /* Only update if we've changed from our initial state */
 344                if (jump_label_type(iter) != jump_label_init_type(iter))
 345                        __jump_label_update(key, iter, iter_stop);
 346        }
 347
 348        return 0;
 349}
 350
 351static void jump_label_del_module(struct module *mod)
 352{
 353        struct jump_entry *iter_start = mod->jump_entries;
 354        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 355        struct jump_entry *iter;
 356        struct static_key *key = NULL;
 357        struct static_key_mod *jlm, **prev;
 358
 359        for (iter = iter_start; iter < iter_stop; iter++) {
 360                if (jump_entry_key(iter) == key)
 361                        continue;
 362
 363                key = jump_entry_key(iter);
 364
 365                if (within_module(iter->key, mod))
 366                        continue;
 367
 368                prev = &key->next;
 369                jlm = key->next;
 370
 371                while (jlm && jlm->mod != mod) {
 372                        prev = &jlm->next;
 373                        jlm = jlm->next;
 374                }
 375
 376                if (jlm) {
 377                        *prev = jlm->next;
 378                        kfree(jlm);
 379                }
 380        }
 381}
 382
 383static void jump_label_invalidate_module_init(struct module *mod)
 384{
 385        struct jump_entry *iter_start = mod->jump_entries;
 386        struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
 387        struct jump_entry *iter;
 388
 389        for (iter = iter_start; iter < iter_stop; iter++) {
 390                if (within_module_init(iter->code, mod))
 391                        iter->code = 0;
 392        }
 393}
 394
 395static int
 396jump_label_module_notify(struct notifier_block *self, unsigned long val,
 397                         void *data)
 398{
 399        struct module *mod = data;
 400        int ret = 0;
 401
 402        switch (val) {
 403        case MODULE_STATE_COMING:
 404                jump_label_lock();
 405                ret = jump_label_add_module(mod);
 406                if (ret)
 407                        jump_label_del_module(mod);
 408                jump_label_unlock();
 409                break;
 410        case MODULE_STATE_GOING:
 411                jump_label_lock();
 412                jump_label_del_module(mod);
 413                jump_label_unlock();
 414                break;
 415        case MODULE_STATE_LIVE:
 416                jump_label_lock();
 417                jump_label_invalidate_module_init(mod);
 418                jump_label_unlock();
 419                break;
 420        }
 421
 422        return notifier_from_errno(ret);
 423}
 424
 425struct notifier_block jump_label_module_nb = {
 426        .notifier_call = jump_label_module_notify,
 427        .priority = 1, /* higher than tracepoints */
 428};
 429
 430static __init int jump_label_init_module(void)
 431{
 432        return register_module_notifier(&jump_label_module_nb);
 433}
 434early_initcall(jump_label_init_module);
 435
 436#endif /* CONFIG_MODULES */
 437
 438/***
 439 * jump_label_text_reserved - check if addr range is reserved
 440 * @start: start text addr
 441 * @end: end text addr
 442 *
 443 * checks if the text addr located between @start and @end
 444 * overlaps with any of the jump label patch addresses. Code
 445 * that wants to modify kernel text should first verify that
 446 * it does not overlap with any of the jump label addresses.
 447 * Caller must hold jump_label_mutex.
 448 *
 449 * returns 1 if there is an overlap, 0 otherwise
 450 */
 451int jump_label_text_reserved(void *start, void *end)
 452{
 453        int ret = __jump_label_text_reserved(__start___jump_table,
 454                        __stop___jump_table, start, end);
 455
 456        if (ret)
 457                return ret;
 458
 459#ifdef CONFIG_MODULES
 460        ret = __jump_label_mod_text_reserved(start, end);
 461#endif
 462        return ret;
 463}
 464
 465static void jump_label_update(struct static_key *key)
 466{
 467        struct jump_entry *stop = __stop___jump_table;
 468        struct jump_entry *entry = static_key_entries(key);
 469#ifdef CONFIG_MODULES
 470        struct module *mod;
 471
 472        __jump_label_mod_update(key);
 473
 474        preempt_disable();
 475        mod = __module_address((unsigned long)key);
 476        if (mod)
 477                stop = mod->jump_entries + mod->num_jump_entries;
 478        preempt_enable();
 479#endif
 480        /* if there are no users, entry can be NULL */
 481        if (entry)
 482                __jump_label_update(key, entry, stop);
 483}
 484
 485#ifdef CONFIG_STATIC_KEYS_SELFTEST
 486static DEFINE_STATIC_KEY_TRUE(sk_true);
 487static DEFINE_STATIC_KEY_FALSE(sk_false);
 488
 489static __init int jump_label_test(void)
 490{
 491        int i;
 492
 493        for (i = 0; i < 2; i++) {
 494                WARN_ON(static_key_enabled(&sk_true.key) != true);
 495                WARN_ON(static_key_enabled(&sk_false.key) != false);
 496
 497                WARN_ON(!static_branch_likely(&sk_true));
 498                WARN_ON(!static_branch_unlikely(&sk_true));
 499                WARN_ON(static_branch_likely(&sk_false));
 500                WARN_ON(static_branch_unlikely(&sk_false));
 501
 502                static_branch_disable(&sk_true);
 503                static_branch_enable(&sk_false);
 504
 505                WARN_ON(static_key_enabled(&sk_true.key) == true);
 506                WARN_ON(static_key_enabled(&sk_false.key) == false);
 507
 508                WARN_ON(static_branch_likely(&sk_true));
 509                WARN_ON(static_branch_unlikely(&sk_true));
 510                WARN_ON(!static_branch_likely(&sk_false));
 511                WARN_ON(!static_branch_unlikely(&sk_false));
 512
 513                static_branch_enable(&sk_true);
 514                static_branch_disable(&sk_false);
 515        }
 516
 517        return 0;
 518}
 519late_initcall(jump_label_test);
 520#endif /* STATIC_KEYS_SELFTEST */
 521
 522#endif /* HAVE_JUMP_LABEL */
 523