jump_label.c

/*
 * jump label support
 *
 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
 * Copyright (C) 2011 Peter Zijlstra <pzijlstr@redhat.com>
 *
 */
#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/jump_label.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);
}

bool jump_label_enabled(struct jump_label_key *key)
{
	return !!atomic_read(&key->enabled);
}

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 jump_label_key *key, int enable);

void jump_label_inc(struct jump_label_key *key)
{
	if (atomic_inc_not_zero(&key->enabled))
		return;

	jump_label_lock();
	if (atomic_add_return(1, &key->enabled) == 1)
		jump_label_update(key, JUMP_LABEL_ENABLE);
	jump_label_unlock();
}

void jump_label_dec(struct jump_label_key *key)
{
	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
		return;

	jump_label_update(key, JUMP_LABEL_DISABLE);
	jump_label_unlock();
}

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;
}

static void __jump_label_update(struct jump_label_key *key,
		struct jump_entry *entry, int enable)
{
	for (; 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);
	}
}

/*
 * Not all archs need this.
 */
void __weak arch_jump_label_text_poke_early(jump_label_t addr)
{
}

static __init int jump_label_init(void)
{
	struct jump_entry *iter_start = __start___jump_table;
	struct jump_entry *iter_stop = __stop___jump_table;
	struct jump_label_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++) {
		arch_jump_label_text_poke_early(iter->code);
		if (iter->key == (jump_label_t)(unsigned long)key)
			continue;

		key = (struct jump_label_key *)(unsigned long)iter->key;
		atomic_set(&key->enabled, 0);
		key->entries = iter;
#ifdef CONFIG_MODULES
		key->next = NULL;
#endif
	}
	jump_label_unlock();

	return 0;
}
early_initcall(jump_label_init);

#ifdef CONFIG_MODULES

struct jump_label_mod {
	struct jump_label_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 jump_label_key *key, int enable)
{
	struct jump_label_mod *mod = key->next;

	while (mod) {
		__jump_label_update(key, mod->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_text_poke_early(iter->code);
}

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 jump_label_key *key = NULL;
	struct jump_label_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++) {
		if (iter->key == (jump_label_t)(unsigned long)key)
			continue;

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

		if (__module_address(iter->key) == mod) {
			atomic_set(&key->enabled, 0);
			key->entries = iter;
			key->next = NULL;
			continue;
		}

		jlm = kzalloc(sizeof(struct jump_label_mod), GFP_KERNEL);
		if (!jlm)
			return -ENOMEM;

		jlm->mod = mod;
		jlm->entries = iter;
		jlm->next = key->next;
		key->next = jlm;

		if (jump_label_enabled(key))
			__jump_label_update(key, iter, 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 jump_label_key *key = NULL;
	struct jump_label_mod *jlm, **prev;

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

		key = (struct jump_label_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 jump_label_key *key, int enable)
{
	struct jump_entry *entry = key->entries;

	/* if there are no users, entry can be NULL */
	if (entry)
		__jump_label_update(key, entry, enable);

#ifdef CONFIG_MODULES
	__jump_label_mod_update(key, enable);
#endif
}

#endif