/*
 * KASAN quarantine.
 *
 * Author: Alexander Potapenko <glider@google.com>
 * Copyright (C) 2016 Google, Inc.
 *
 * Based on code by Dmitry Chernenkov.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 */

#include <linux/gfp.h>
#include <linux/hash.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/printk.h>
#include <linux/shrinker.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/types.h>

#include "../slab.h"
#include "kasan.h"

/* Data structure and operations for quarantine queues. */

/*
 * Each queue is a signle-linked list, which also stores the total size of
 * objects inside of it.
 */
struct qlist_head {
        struct qlist_node *head;
        struct qlist_node *tail;
        size_t bytes;
};

#define QLIST_INIT { NULL, NULL, 0 }

static bool qlist_empty(struct qlist_head *q)
{
        return !q->head;
}

static void qlist_init(struct qlist_head *q)
{
        q->head = q->tail = NULL;
        q->bytes = 0;
}

static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
                size_t size)
{
        if (unlikely(qlist_empty(q)))
                q->head = qlink;
        else
                q->tail->next = qlink;
        q->tail = qlink;
        qlink->next = NULL;
        q->bytes += size;
}

static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
{
        if (unlikely(qlist_empty(from)))
                return;

        if (qlist_empty(to)) {
                *to = *from;
                qlist_init(from);
                return;
        }

        to->tail->next = from->head;
        to->tail = from->tail;
        to->bytes += from->bytes;

        qlist_init(from);
}

static void qlist_move(struct qlist_head *from, struct qlist_node *last,
                struct qlist_head *to, size_t size)
{
        if (unlikely(last == from->tail)) {
                qlist_move_all(from, to);
                return;
        }
        if (qlist_empty(to))
                to->head = from->head;
        else
                to->tail->next = from->head;
        to->tail = last;
        from->head = last->next;
        last->next = NULL;
        from->bytes -= size;
        to->bytes += size;
}


/*
 * The object quarantine consists of per-cpu queues and a global queue,
 * guarded by quarantine_lock.
 */
static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);

static struct qlist_head global_quarantine;
static DEFINE_SPINLOCK(quarantine_lock);

/* Maximum size of the global queue. */
static unsigned long quarantine_size;

/*
 * The fraction of physical memory the quarantine is allowed to occupy.
 * Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
 * the ratio low to avoid OOM.
 */
#define QUARANTINE_FRACTION 32

#define QUARANTINE_LOW_SIZE (READ_ONCE(quarantine_size) * 3 / 4)
#define QUARANTINE_PERCPU_SIZE (1 << 20)

static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
{
        return virt_to_head_page(qlink)->slab_cache;
}

static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
{
        struct kasan_free_meta *free_info =
                container_of(qlink, struct kasan_free_meta,
                             quarantine_link);

        return ((void *)free_info) - cache->kasan_info.free_meta_offset;
}

static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
{
        void *object = qlink_to_object(qlink, cache);
        unsigned long flags;

        if (IS_ENABLED(CONFIG_SLAB))
                local_irq_save(flags);

        ___cache_free(cache, object, _THIS_IP_);

        if (IS_ENABLED(CONFIG_SLAB))
                local_irq_restore(flags);
}

static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
{
        struct qlist_node *qlink;

        if (unlikely(qlist_empty(q)))
                return;

        qlink = q->head;
        while (qlink) {
                struct kmem_cache *obj_cache =
                        cache ? cache : qlink_to_cache(qlink);
                struct qlist_node *next = qlink->next;

                qlink_free(qlink, obj_cache);
                qlink = next;
        }
        qlist_init(q);
}

void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
{
        unsigned long flags;
        struct qlist_head *q;
        struct qlist_head temp = QLIST_INIT;

        local_irq_save(flags);

        q = this_cpu_ptr(&cpu_quarantine);
        qlist_put(q, &info->quarantine_link, cache->size);
        if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE))
                qlist_move_all(q, &temp);

        local_irq_restore(flags);

        if (unlikely(!qlist_empty(&temp))) {
                spin_lock_irqsave(&quarantine_lock, flags);
                qlist_move_all(&temp, &global_quarantine);
                spin_unlock_irqrestore(&quarantine_lock, flags);
        }
}

void quarantine_reduce(void)
{
        size_t new_quarantine_size, percpu_quarantines;
        unsigned long flags;
        struct qlist_head to_free = QLIST_INIT;
        size_t size_to_free = 0;
        struct qlist_node *last;

        if (likely(READ_ONCE(global_quarantine.bytes) <=
                   READ_ONCE(quarantine_size)))
                return;

        spin_lock_irqsave(&quarantine_lock, flags);

        /*
         * Update quarantine size in case of hotplug. Allocate a fraction of
         * the installed memory to quarantine minus per-cpu queue limits.
         */
        new_quarantine_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
                QUARANTINE_FRACTION;
        percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
        new_quarantine_size = (new_quarantine_size < percpu_quarantines) ?
                0 : new_quarantine_size - percpu_quarantines;
        WRITE_ONCE(quarantine_size, new_quarantine_size);

        last = global_quarantine.head;
        while (last) {
                struct kmem_cache *cache = qlink_to_cache(last);

                size_to_free += cache->size;
                if (!last->next || size_to_free >
                    global_quarantine.bytes - QUARANTINE_LOW_SIZE)
                        break;
                last = last->next;
        }
        qlist_move(&global_quarantine, last, &to_free, size_to_free);

        spin_unlock_irqrestore(&quarantine_lock, flags);

        qlist_free_all(&to_free, NULL);
}

static void qlist_move_cache(struct qlist_head *from,
                                   struct qlist_head *to,
                                   struct kmem_cache *cache)
{
        struct qlist_node *curr;

        if (unlikely(qlist_empty(from)))
                return;

        curr = from->head;
        qlist_init(from);
        while (curr) {
                struct qlist_node *next = curr->next;
                struct kmem_cache *obj_cache = qlink_to_cache(curr);

                if (obj_cache == cache)
                        qlist_put(to, curr, obj_cache->size);
                else
                        qlist_put(from, curr, obj_cache->size);

                curr = next;
        }
}

static void per_cpu_remove_cache(void *arg)
{
        struct kmem_cache *cache = arg;
        struct qlist_head to_free = QLIST_INIT;
        struct qlist_head *q;

        q = this_cpu_ptr(&cpu_quarantine);
        qlist_move_cache(q, &to_free, cache);
        qlist_free_all(&to_free, cache);
}

void quarantine_remove_cache(struct kmem_cache *cache)
{
        unsigned long flags;
        struct qlist_head to_free = QLIST_INIT;

        on_each_cpu(per_cpu_remove_cache, cache, 1);

        spin_lock_irqsave(&quarantine_lock, flags);
        qlist_move_cache(&global_quarantine, &to_free, cache);
        spin_unlock_irqrestore(&quarantine_lock, flags);

        qlist_free_all(&to_free, cache);
}