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

FreeBSD/Linux Kernel Cross Reference
sys/kernel/jump_label.c
