jump_label.c

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/*
 * jump label support
 *
 * Copyright (C) 2009 Jason Baron <[email protected]>
 * Copyright (C) 2011 Peter Zijlstra <[email protected]>
 *
 */
#include <linux/memory.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/err.h>
#include <linux/static_key.h>

#ifdef HAVE_JUMP_LABEL

/* mutex to protect coming/going of the the jump_label table */
static DEFINE_MUTEX(jump_label_mutex);

void jump_label_lock(void)
{
    mutex_lock(&jump_label_mutex);
}

void jump_label_unlock(void)
{
    mutex_unlock(&jump_label_mutex);
}

static int jump_label_cmp(const void *a, const void *b)
{
    const struct jump_entry *jea = a;
    const struct jump_entry *jeb = b;

    if (jea->key < jeb->key)
        return -1;

    if (jea->key > jeb->key)
        return 1;

    return 0;
}

static void
jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
{
    unsigned long size;

    size = (((unsigned long)stop - (unsigned long)start)
                    / sizeof(struct jump_entry));
    sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
}

static void jump_label_update(struct static_key *key, int enable);

void static_key_slow_inc(struct static_key *key)
{
    if (atomic_inc_not_zero(&key->enabled))
        return;

    jump_label_lock();
    if (atomic_read(&key->enabled) == 0) {
        if (!jump_label_get_branch_default(key))
            jump_label_update(key, JUMP_LABEL_ENABLE);
        else
            jump_label_update(key, JUMP_LABEL_DISABLE);
    }
    atomic_inc(&key->enabled);
    jump_label_unlock();
}
EXPORT_SYMBOL_GPL(static_key_slow_inc);

static void __static_key_slow_dec(struct static_key *key,
        unsigned long rate_limit, struct delayed_work *work)
{
    if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) {
        WARN(atomic_read(&key->enabled) < 0,
             "jump label: negative count!\n");
        return;
    }

    if (rate_limit) {
        atomic_inc(&key->enabled);
        schedule_delayed_work(work, rate_limit);
    } else {
        if (!jump_label_get_branch_default(key))
            jump_label_update(key, JUMP_LABEL_DISABLE);
        else
            jump_label_update(key, JUMP_LABEL_ENABLE);
    }
    jump_label_unlock();
}

static void jump_label_update_timeout(struct work_struct *work)
{
    struct static_key_deferred *key =
        container_of(work, struct static_key_deferred, work.work);
    __static_key_slow_dec(&key->key, 0, NULL);
}

void static_key_slow_dec(struct static_key *key)
{
    __static_key_slow_dec(key, 0, NULL);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec);

void static_key_slow_dec_deferred(struct static_key_deferred *key)
{
    __static_key_slow_dec(&key->key, key->timeout, &key->work);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);

void jump_label_rate_limit(struct static_key_deferred *key,
        unsigned long rl)
{
    key->timeout = rl;
    INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
}
EXPORT_SYMBOL_GPL(jump_label_rate_limit);

static int addr_conflict(struct jump_entry *entry, void *start, void *end)
{
    if (entry->code <= (unsigned long)end &&
        entry->code + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
        return 1;

    return 0;
}

static int __jump_label_text_reserved(struct jump_entry *iter_start,
        struct jump_entry *iter_stop, void *start, void *end)
{
    struct jump_entry *iter;

    iter = iter_start;
    while (iter < iter_stop) {
        if (addr_conflict(iter, start, end))
            return 1;
        iter++;
    }

    return 0;
}

/* 
 * Update code which is definitely not currently executing.
 * Architectures which need heavyweight synchronization to modify
 * running code can override this to make the non-live update case
 * cheaper.
 */
void __weak __init_or_module arch_jump_label_transform_static(struct jump_entry *entry,
                        enum jump_label_type type)
{
    arch_jump_label_transform(entry, type); 
}

static void __jump_label_update(struct static_key *key,
                struct jump_entry *entry,
                struct jump_entry *stop, int enable)
{
    for (; (entry < stop) &&
          (entry->key == (jump_label_t)(unsigned long)key);
          entry++) {
        /*
         * entry->code set to 0 invalidates module init text sections
         * kernel_text_address() verifies we are not in core kernel
         * init code, see jump_label_invalidate_module_init().
         */
        if (entry->code && kernel_text_address(entry->code))
            arch_jump_label_transform(entry, enable);
    }
}

static enum jump_label_type jump_label_type(struct static_key *key)
{
    bool true_branch = jump_label_get_branch_default(key);
    bool state = static_key_enabled(key);

    if ((!true_branch && state) || (true_branch && !state))
        return JUMP_LABEL_ENABLE;

    return JUMP_LABEL_DISABLE;
}

void __init jump_label_init(void)
{
    struct jump_entry *iter_start = __start___jump_table;
    struct jump_entry *iter_stop = __stop___jump_table;
    struct static_key *key = NULL;
    struct jump_entry *iter;

    jump_label_lock();
    jump_label_sort_entries(iter_start, iter_stop);

    for (iter = iter_start; iter < iter_stop; iter++) {
        struct static_key *iterk;

        iterk = (struct static_key *)(unsigned long)iter->key;
        arch_jump_label_transform_static(iter, jump_label_type(iterk));
        if (iterk == key)
            continue;

        key = iterk;
        /*
         * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
         */
        *((unsigned long *)&key->entries) += (unsigned long)iter;
#ifdef CONFIG_MODULES
        key->next = NULL;
#endif
    }
    jump_label_unlock();
}

#ifdef CONFIG_MODULES

struct static_key_mod {
    struct static_key_mod *next;
    struct jump_entry *entries;
    struct module *mod;
};

static int __jump_label_mod_text_reserved(void *start, void *end)
{
    struct module *mod;

    mod = __module_text_address((unsigned long)start);
    if (!mod)
        return 0;

    WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);

    return __jump_label_text_reserved(mod->jump_entries,
                mod->jump_entries + mod->num_jump_entries,
                start, end);
}

static void __jump_label_mod_update(struct static_key *key, int enable)
{
    struct static_key_mod *mod = key->next;

    while (mod) {
        struct module *m = mod->mod;

        __jump_label_update(key, mod->entries,
                    m->jump_entries + m->num_jump_entries,
                    enable);
        mod = mod->next;
    }
}

/***
 * apply_jump_label_nops - patch module jump labels with arch_get_jump_label_nop()
 * @mod: module to patch
 *
 * Allow for run-time selection of the optimal nops. Before the module
 * loads patch these with arch_get_jump_label_nop(), which is specified by
 * the arch specific jump label code.
 */
void jump_label_apply_nops(struct module *mod)
{
    struct jump_entry *iter_start = mod->jump_entries;
    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
    struct jump_entry *iter;

    /* if the module doesn't have jump label entries, just return */
    if (iter_start == iter_stop)
        return;

    for (iter = iter_start; iter < iter_stop; iter++) {
        arch_jump_label_transform_static(iter, JUMP_LABEL_DISABLE);
    }
}

static int jump_label_add_module(struct module *mod)
{
    struct jump_entry *iter_start = mod->jump_entries;
    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
    struct jump_entry *iter;
    struct static_key *key = NULL;
    struct static_key_mod *jlm;

    /* if the module doesn't have jump label entries, just return */
    if (iter_start == iter_stop)
        return 0;

    jump_label_sort_entries(iter_start, iter_stop);

    for (iter = iter_start; iter < iter_stop; iter++) {
        struct static_key *iterk;

        iterk = (struct static_key *)(unsigned long)iter->key;
        if (iterk == key)
            continue;

        key = iterk;
        if (__module_address(iter->key) == mod) {
            /*
             * Set key->entries to iter, but preserve JUMP_LABEL_TRUE_BRANCH.
             */
            *((unsigned long *)&key->entries) += (unsigned long)iter;
            key->next = NULL;
            continue;
        }
        jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
        if (!jlm)
            return -ENOMEM;
        jlm->mod = mod;
        jlm->entries = iter;
        jlm->next = key->next;
        key->next = jlm;

        if (jump_label_type(key) == JUMP_LABEL_ENABLE)
            __jump_label_update(key, iter, iter_stop, JUMP_LABEL_ENABLE);
    }

    return 0;
}

static void jump_label_del_module(struct module *mod)
{
    struct jump_entry *iter_start = mod->jump_entries;
    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
    struct jump_entry *iter;
    struct static_key *key = NULL;
    struct static_key_mod *jlm, **prev;

    for (iter = iter_start; iter < iter_stop; iter++) {
        if (iter->key == (jump_label_t)(unsigned long)key)
            continue;

        key = (struct static_key *)(unsigned long)iter->key;

        if (__module_address(iter->key) == mod)
            continue;

        prev = &key->next;
        jlm = key->next;

        while (jlm && jlm->mod != mod) {
            prev = &jlm->next;
            jlm = jlm->next;
        }

        if (jlm) {
            *prev = jlm->next;
            kfree(jlm);
        }
    }
}

static void jump_label_invalidate_module_init(struct module *mod)
{
    struct jump_entry *iter_start = mod->jump_entries;
    struct jump_entry *iter_stop = iter_start + mod->num_jump_entries;
    struct jump_entry *iter;

    for (iter = iter_start; iter < iter_stop; iter++) {
        if (within_module_init(iter->code, mod))
            iter->code = 0;
    }
}

static int
jump_label_module_notify(struct notifier_block *self, unsigned long val,
             void *data)
{
    struct module *mod = data;
    int ret = 0;

    switch (val) {
    case MODULE_STATE_COMING:
        jump_label_lock();
        ret = jump_label_add_module(mod);
        if (ret)
            jump_label_del_module(mod);
        jump_label_unlock();
        break;
    case MODULE_STATE_GOING:
        jump_label_lock();
        jump_label_del_module(mod);
        jump_label_unlock();
        break;
    case MODULE_STATE_LIVE:
        jump_label_lock();
        jump_label_invalidate_module_init(mod);
        jump_label_unlock();
        break;
    }

    return notifier_from_errno(ret);
}

struct notifier_block jump_label_module_nb = {
    .notifier_call = jump_label_module_notify,
    .priority = 1, /* higher than tracepoints */
};

static __init int jump_label_init_module(void)
{
    return register_module_notifier(&jump_label_module_nb);
}
early_initcall(jump_label_init_module);

#endif /* CONFIG_MODULES */

/***
 * jump_label_text_reserved - check if addr range is reserved
 * @start: start text addr
 * @end: end text addr
 *
 * checks if the text addr located between @start and @end
 * overlaps with any of the jump label patch addresses. Code
 * that wants to modify kernel text should first verify that
 * it does not overlap with any of the jump label addresses.
 * Caller must hold jump_label_mutex.
 *
 * returns 1 if there is an overlap, 0 otherwise
 */
int jump_label_text_reserved(void *start, void *end)
{
    int ret = __jump_label_text_reserved(__start___jump_table,
            __stop___jump_table, start, end);

    if (ret)
        return ret;

#ifdef CONFIG_MODULES
    ret = __jump_label_mod_text_reserved(start, end);
#endif
    return ret;
}

static void jump_label_update(struct static_key *key, int enable)
{
    struct jump_entry *stop = __stop___jump_table;
    struct jump_entry *entry = jump_label_get_entries(key);

#ifdef CONFIG_MODULES
    struct module *mod = __module_address((unsigned long)key);

    __jump_label_mod_update(key, enable);

    if (mod)
        stop = mod->jump_entries + mod->num_jump_entries;
#endif
    /* if there are no users, entry can be NULL */
    if (entry)
        __jump_label_update(key, entry, stop, enable);
}

#endif