x86/doc: Remove obvious weirdnesses from the x86 MM layout documentation

[linux/fpc-iii.git] / kernel / jump_label.c

/*
 * jump label support
 *
 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
 * Copyright (C) 2011 Peter Zijlstra
 *
 */
#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>
#include <linux/jump_label_ratelimit.h>
#include <linux/bug.h>
#include <linux/cpu.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);

/*
 * There are similar definitions for the !HAVE_JUMP_LABEL case in jump_label.h.
 * The use of 'atomic_read()' requires atomic.h and its problematic for some
 * kernel headers such as kernel.h and others. Since static_key_count() is not
 * used in the branch statements as it is for the !HAVE_JUMP_LABEL case its ok
 * to have it be a function here. Similarly, for 'static_key_enable()' and
 * 'static_key_disable()', which require bug.h. This should allow jump_label.h
 * to be included from most/all places for HAVE_JUMP_LABEL.
 */
int static_key_count(struct static_key *key)
{
        /*
         * -1 means the first static_key_slow_inc() is in progress.
         *  static_key_enabled() must return true, so return 1 here.
         */
        int n = atomic_read(&key->enabled);

        return n >= 0 ? n : 1;
}
EXPORT_SYMBOL_GPL(static_key_count);

static void static_key_slow_inc_cpuslocked(struct static_key *key)
{
        int v, v1;

        STATIC_KEY_CHECK_USE();

        /*
         * Careful if we get concurrent static_key_slow_inc() calls;
         * later calls must wait for the first one to _finish_ the
         * jump_label_update() process.  At the same time, however,
         * the jump_label_update() call below wants to see
         * static_key_enabled(&key) for jumps to be updated properly.
         *
         * So give a special meaning to negative key->enabled: it sends
         * static_key_slow_inc() down the slow path, and it is non-zero
         * so it counts as "enabled" in jump_label_update().  Note that
         * atomic_inc_unless_negative() checks >= 0, so roll our own.
         */
        for (v = atomic_read(&key->enabled); v > 0; v = v1) {
                v1 = atomic_cmpxchg(&key->enabled, v, v + 1);
                if (likely(v1 == v))
                        return;
        }

        jump_label_lock();
        if (atomic_read(&key->enabled) == 0) {
                atomic_set(&key->enabled, -1);
                jump_label_update(key);
                /*
                 * Ensure that if the above cmpxchg loop observes our positive
                 * value, it must also observe all the text changes.
                 */
                atomic_set_release(&key->enabled, 1);
        } else {
                atomic_inc(&key->enabled);
        }
        jump_label_unlock();
}

void static_key_slow_inc(struct static_key *key)
{
        cpus_read_lock();
        static_key_slow_inc_cpuslocked(key);
        cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(static_key_slow_inc);

void static_key_enable_cpuslocked(struct static_key *key)
{
        STATIC_KEY_CHECK_USE();

        if (atomic_read(&key->enabled) > 0) {
                WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
                return;
        }

        jump_label_lock();
        if (atomic_read(&key->enabled) == 0) {
                atomic_set(&key->enabled, -1);
                jump_label_update(key);
                /*
                 * See static_key_slow_inc().
                 */
                atomic_set_release(&key->enabled, 1);
        }
        jump_label_unlock();
}
EXPORT_SYMBOL_GPL(static_key_enable_cpuslocked);

void static_key_enable(struct static_key *key)
{
        cpus_read_lock();
        static_key_enable_cpuslocked(key);
        cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(static_key_enable);

void static_key_disable_cpuslocked(struct static_key *key)
{
        STATIC_KEY_CHECK_USE();

        if (atomic_read(&key->enabled) != 1) {
                WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
                return;
        }

        jump_label_lock();
        if (atomic_cmpxchg(&key->enabled, 1, 0))
                jump_label_update(key);
        jump_label_unlock();
}
EXPORT_SYMBOL_GPL(static_key_disable_cpuslocked);

void static_key_disable(struct static_key *key)
{
        cpus_read_lock();
        static_key_disable_cpuslocked(key);
        cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(static_key_disable);

static void static_key_slow_dec_cpuslocked(struct static_key *key,
                                           unsigned long rate_limit,
                                           struct delayed_work *work)
{
        /*
         * The negative count check is valid even when a negative
         * key->enabled is in use by static_key_slow_inc(); a
         * __static_key_slow_dec() before the first static_key_slow_inc()
         * returns is unbalanced, because all other static_key_slow_inc()
         * instances block while the update is in progress.
         */
        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 {
                jump_label_update(key);
        }
        jump_label_unlock();
}

static void __static_key_slow_dec(struct static_key *key,
                                  unsigned long rate_limit,
                                  struct delayed_work *work)
{
        cpus_read_lock();
        static_key_slow_dec_cpuslocked(key, rate_limit, work);
        cpus_read_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_CHECK_USE();
        __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_CHECK_USE();
        __static_key_slow_dec(&key->key, key->timeout, &key->work);
}
EXPORT_SYMBOL_GPL(static_key_slow_dec_deferred);

void static_key_deferred_flush(struct static_key_deferred *key)
{
        STATIC_KEY_CHECK_USE();
        flush_delayed_work(&key->work);
}
EXPORT_SYMBOL_GPL(static_key_deferred_flush);

void jump_label_rate_limit(struct static_key_deferred *key,
                unsigned long rl)
{
        STATIC_KEY_CHECK_USE();
        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 inline struct jump_entry *static_key_entries(struct static_key *key)
{
        WARN_ON_ONCE(key->type & JUMP_TYPE_LINKED);
        return (struct jump_entry *)(key->type & ~JUMP_TYPE_MASK);
}

static inline bool static_key_type(struct static_key *key)
{
        return key->type & JUMP_TYPE_TRUE;
}

static inline bool static_key_linked(struct static_key *key)
{
        return key->type & JUMP_TYPE_LINKED;
}

static inline void static_key_clear_linked(struct static_key *key)
{
        key->type &= ~JUMP_TYPE_LINKED;
}

static inline void static_key_set_linked(struct static_key *key)
{
        key->type |= JUMP_TYPE_LINKED;
}

static inline struct static_key *jump_entry_key(struct jump_entry *entry)
{
        return (struct static_key *)((unsigned long)entry->key & ~1UL);
}

static bool jump_entry_branch(struct jump_entry *entry)
{
        return (unsigned long)entry->key & 1UL;
}

/***
 * A 'struct static_key' uses a union such that it either points directly
 * to a table of 'struct jump_entry' or to a linked list of modules which in
 * turn point to 'struct jump_entry' tables.
 *
 * The two lower bits of the pointer are used to keep track of which pointer
 * type is in use and to store the initial branch direction, we use an access
 * function which preserves these bits.
 */
static void static_key_set_entries(struct static_key *key,
                                   struct jump_entry *entries)
{
        unsigned long type;

        WARN_ON_ONCE((unsigned long)entries & JUMP_TYPE_MASK);
        type = key->type & JUMP_TYPE_MASK;
        key->entries = entries;
        key->type |= type;
}

static enum jump_label_type jump_label_type(struct jump_entry *entry)
{
        struct static_key *key = jump_entry_key(entry);
        bool enabled = static_key_enabled(key);
        bool branch = jump_entry_branch(entry);

        /* See the comment in linux/jump_label.h */
        return enabled ^ branch;
}

static void __jump_label_update(struct static_key *key,
                                struct jump_entry *entry,
                                struct jump_entry *stop)
{
        for (; (entry < stop) && (jump_entry_key(entry) == 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, jump_label_type(entry));
        }
}

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;

        /*
         * Since we are initializing the static_key.enabled field with
         * with the 'raw' int values (to avoid pulling in atomic.h) in
         * jump_label.h, let's make sure that is safe. There are only two
         * cases to check since we initialize to 0 or 1.
         */
        BUILD_BUG_ON((int)ATOMIC_INIT(0) != 0);
        BUILD_BUG_ON((int)ATOMIC_INIT(1) != 1);

        if (static_key_initialized)
                return;

        cpus_read_lock();
        jump_label_lock();
        jump_label_sort_entries(iter_start, iter_stop);

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

                /* rewrite NOPs */
                if (jump_label_type(iter) == JUMP_LABEL_NOP)
                        arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);

                iterk = jump_entry_key(iter);
                if (iterk == key)
                        continue;

                key = iterk;
                static_key_set_entries(key, iter);
        }
        static_key_initialized = true;
        jump_label_unlock();
        cpus_read_unlock();
}

#ifdef CONFIG_MODULES

static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
{
        struct static_key *key = jump_entry_key(entry);
        bool type = static_key_type(key);
        bool branch = jump_entry_branch(entry);

        /* See the comment in linux/jump_label.h */
        return type ^ branch;
}

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

static inline struct static_key_mod *static_key_mod(struct static_key *key)
{
        WARN_ON_ONCE(!(key->type & JUMP_TYPE_LINKED));
        return (struct static_key_mod *)(key->type & ~JUMP_TYPE_MASK);
}

/***
 * key->type and key->next are the same via union.
 * This sets key->next and preserves the type bits.
 *
 * See additional comments above static_key_set_entries().
 */
static void static_key_set_mod(struct static_key *key,
                               struct static_key_mod *mod)
{
        unsigned long type;

        WARN_ON_ONCE((unsigned long)mod & JUMP_TYPE_MASK);
        type = key->type & JUMP_TYPE_MASK;
        key->next = mod;
        key->type |= type;
}

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

        preempt_disable();
        mod = __module_text_address((unsigned long)start);
        WARN_ON_ONCE(__module_text_address((unsigned long)end) != mod);
        preempt_enable();

        if (!mod)
                return 0;


        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)
{
        struct static_key_mod *mod;

        for (mod = static_key_mod(key); mod; mod = mod->next) {
                struct jump_entry *stop;
                struct module *m;

                /*
                 * NULL if the static_key is defined in a module
                 * that does not use it
                 */
                if (!mod->entries)
                        continue;

                m = mod->mod;
                if (!m)
                        stop = __stop___jump_table;
                else
                        stop = m->jump_entries + m->num_jump_entries;
                __jump_label_update(key, mod->entries, stop);
        }
}

/***
 * 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++) {
                /* Only write NOPs for arch_branch_static(). */
                if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
                        arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
        }
}

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, *jlm2;

        /* 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 = jump_entry_key(iter);
                if (iterk == key)
                        continue;

                key = iterk;
                if (within_module(iter->key, mod)) {
                        static_key_set_entries(key, iter);
                        continue;
                }
                jlm = kzalloc(sizeof(struct static_key_mod), GFP_KERNEL);
                if (!jlm)
                        return -ENOMEM;
                if (!static_key_linked(key)) {
                        jlm2 = kzalloc(sizeof(struct static_key_mod),
                                       GFP_KERNEL);
                        if (!jlm2) {
                                kfree(jlm);
                                return -ENOMEM;
                        }
                        preempt_disable();
                        jlm2->mod = __module_address((unsigned long)key);
                        preempt_enable();
                        jlm2->entries = static_key_entries(key);
                        jlm2->next = NULL;
                        static_key_set_mod(key, jlm2);
                        static_key_set_linked(key);
                }
                jlm->mod = mod;
                jlm->entries = iter;
                jlm->next = static_key_mod(key);
                static_key_set_mod(key, jlm);
                static_key_set_linked(key);

                /* Only update if we've changed from our initial state */
                if (jump_label_type(iter) != jump_label_init_type(iter))
                        __jump_label_update(key, iter, iter_stop);
        }

        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 (jump_entry_key(iter) == key)
                        continue;

                key = jump_entry_key(iter);

                if (within_module(iter->key, mod))
                        continue;

                /* No memory during module load */
                if (WARN_ON(!static_key_linked(key)))
                        continue;

                prev = &key->next;
                jlm = static_key_mod(key);

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

                /* No memory during module load */
                if (WARN_ON(!jlm))
                        continue;

                if (prev == &key->next)
                        static_key_set_mod(key, jlm->next);
                else
                        *prev = jlm->next;

                kfree(jlm);

                jlm = static_key_mod(key);
                /* if only one etry is left, fold it back into the static_key */
                if (jlm->next == NULL) {
                        static_key_set_entries(key, jlm->entries);
                        static_key_clear_linked(key);
                        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;

        cpus_read_lock();
        jump_label_lock();

        switch (val) {
        case MODULE_STATE_COMING:
                ret = jump_label_add_module(mod);
                if (ret) {
                        WARN(1, "Failed to allocatote memory: jump_label may not work properly.\n");
                        jump_label_del_module(mod);
                }
                break;
        case MODULE_STATE_GOING:
                jump_label_del_module(mod);
                break;
        case MODULE_STATE_LIVE:
                jump_label_invalidate_module_init(mod);
                break;
        }

        jump_label_unlock();
        cpus_read_unlock();

        return notifier_from_errno(ret);
}

static 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)
{
        struct jump_entry *stop = __stop___jump_table;
        struct jump_entry *entry;
#ifdef CONFIG_MODULES
        struct module *mod;

        if (static_key_linked(key)) {
                __jump_label_mod_update(key);
                return;
        }

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

#ifdef CONFIG_STATIC_KEYS_SELFTEST
static DEFINE_STATIC_KEY_TRUE(sk_true);
static DEFINE_STATIC_KEY_FALSE(sk_false);

static __init int jump_label_test(void)
{
        int i;

        for (i = 0; i < 2; i++) {
                WARN_ON(static_key_enabled(&sk_true.key) != true);
                WARN_ON(static_key_enabled(&sk_false.key) != false);

                WARN_ON(!static_branch_likely(&sk_true));
                WARN_ON(!static_branch_unlikely(&sk_true));
                WARN_ON(static_branch_likely(&sk_false));
                WARN_ON(static_branch_unlikely(&sk_false));

                static_branch_disable(&sk_true);
                static_branch_enable(&sk_false);

                WARN_ON(static_key_enabled(&sk_true.key) == true);
                WARN_ON(static_key_enabled(&sk_false.key) == false);

                WARN_ON(static_branch_likely(&sk_true));
                WARN_ON(static_branch_unlikely(&sk_true));
                WARN_ON(!static_branch_likely(&sk_false));
                WARN_ON(!static_branch_unlikely(&sk_false));

                static_branch_enable(&sk_true);
                static_branch_disable(&sk_false);
        }

        return 0;
}
late_initcall(jump_label_test);
#endif /* STATIC_KEYS_SELFTEST */

#endif /* HAVE_JUMP_LABEL */