/* mm/ashmem.c
 *
 * Anonymous Shared Memory Subsystem, ashmem
 *
 * Copyright (C) 2008 Google, Inc.
 *
 * Robert Love <rlove@google.com>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * 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.
 */

#define pr_fmt(fmt) "ashmem: " fmt

#include <linux/module.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/falloc.h>
#include <linux/miscdevice.h>
#include <linux/security.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/uaccess.h>
#include <linux/personality.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/shmem_fs.h>
#include "ashmem.h"

#define ASHMEM_NAME_PREFIX "dev/ashmem/"
#define ASHMEM_NAME_PREFIX_LEN (sizeof(ASHMEM_NAME_PREFIX) - 1)
#define ASHMEM_FULL_NAME_LEN (ASHMEM_NAME_LEN + ASHMEM_NAME_PREFIX_LEN)

/*
 * ashmem_area - anonymous shared memory area
 * Lifecycle: From our parent file's open() until its release()
 * Locking: Protected by `ashmem_mutex'
 * Big Note: Mappings do NOT pin this structure; it dies on close()
 */
struct ashmem_area {
        char name[ASHMEM_FULL_NAME_LEN]; /* optional name in /proc/pid/maps */
        struct list_head unpinned_list;  /* list of all ashmem areas */
        struct file *file;               /* the shmem-based backing file */
        size_t size;                     /* size of the mapping, in bytes */
        unsigned long prot_mask;         /* allowed prot bits, as vm_flags */
};

/*
 * ashmem_range - represents an interval of unpinned (evictable) pages
 * Lifecycle: From unpin to pin
 * Locking: Protected by `ashmem_mutex'
 */
struct ashmem_range {
        struct list_head lru;           /* entry in LRU list */
        struct list_head unpinned;      /* entry in its area's unpinned list */
        struct ashmem_area *asma;       /* associated area */
        size_t pgstart;                 /* starting page, inclusive */
        size_t pgend;                   /* ending page, inclusive */
        unsigned int purged;            /* ASHMEM_NOT or ASHMEM_WAS_PURGED */
};

/* LRU list of unpinned pages, protected by ashmem_mutex */
static LIST_HEAD(ashmem_lru_list);

/* Count of pages on our LRU list, protected by ashmem_mutex */
static unsigned long lru_count;

/*
 * ashmem_mutex - protects the list of and each individual ashmem_area
 *
 * Lock Ordering: ashmex_mutex -> i_mutex -> i_alloc_sem
 */
static DEFINE_MUTEX(ashmem_mutex);

static struct kmem_cache *ashmem_area_cachep __read_mostly;
static struct kmem_cache *ashmem_range_cachep __read_mostly;

#define range_size(range) \
        ((range)->pgend - (range)->pgstart + 1)

#define range_on_lru(range) \
        ((range)->purged == ASHMEM_NOT_PURGED)

#define page_range_subsumes_range(range, start, end) \
        (((range)->pgstart >= (start)) && ((range)->pgend <= (end)))

#define page_range_subsumed_by_range(range, start, end) \
        (((range)->pgstart <= (start)) && ((range)->pgend >= (end)))

#define page_in_range(range, page) \
        (((range)->pgstart <= (page)) && ((range)->pgend >= (page)))

#define page_range_in_range(range, start, end) \
        (page_in_range(range, start) || page_in_range(range, end) || \
                page_range_subsumes_range(range, start, end))

#define range_before_page(range, page) \
        ((range)->pgend < (page))

#define PROT_MASK               (PROT_EXEC | PROT_READ | PROT_WRITE)

static inline void lru_add(struct ashmem_range *range)
{
        list_add_tail(&range->lru, &ashmem_lru_list);
        lru_count += range_size(range);
}

static inline void lru_del(struct ashmem_range *range)
{
        list_del(&range->lru);
        lru_count -= range_size(range);
}

/*
 * range_alloc - allocate and initialize a new ashmem_range structure
 *
 * 'asma' - associated ashmem_area
 * 'prev_range' - the previous ashmem_range in the sorted asma->unpinned list
 * 'purged' - initial purge value (ASMEM_NOT_PURGED or ASHMEM_WAS_PURGED)
 * 'start' - starting page, inclusive
 * 'end' - ending page, inclusive
 *
 * Caller must hold ashmem_mutex.
 */
static int range_alloc(struct ashmem_area *asma,
                       struct ashmem_range *prev_range, unsigned int purged,
                       size_t start, size_t end)
{
        struct ashmem_range *range;

        range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL);
        if (unlikely(!range))
                return -ENOMEM;

        range->asma = asma;
        range->pgstart = start;
        range->pgend = end;
        range->purged = purged;

        list_add_tail(&range->unpinned, &prev_range->unpinned);

        if (range_on_lru(range))
                lru_add(range);

        return 0;
}

static void range_del(struct ashmem_range *range)
{
        list_del(&range->unpinned);
        if (range_on_lru(range))
                lru_del(range);
        kmem_cache_free(ashmem_range_cachep, range);
}

/*
 * range_shrink - shrinks a range
 *
 * Caller must hold ashmem_mutex.
 */
static inline void range_shrink(struct ashmem_range *range,
                                size_t start, size_t end)
{
        size_t pre = range_size(range);

        range->pgstart = start;
        range->pgend = end;

        if (range_on_lru(range))
                lru_count -= pre - range_size(range);
}

static int ashmem_open(struct inode *inode, struct file *file)
{
        struct ashmem_area *asma;
        int ret;

        ret = generic_file_open(inode, file);
        if (unlikely(ret))
                return ret;

        asma = kmem_cache_zalloc(ashmem_area_cachep, GFP_KERNEL);
        if (unlikely(!asma))
                return -ENOMEM;

        INIT_LIST_HEAD(&asma->unpinned_list);
        memcpy(asma->name, ASHMEM_NAME_PREFIX, ASHMEM_NAME_PREFIX_LEN);
        asma->prot_mask = PROT_MASK;
        file->private_data = asma;

        return 0;
}

static int ashmem_release(struct inode *ignored, struct file *file)
{
        struct ashmem_area *asma = file->private_data;
        struct ashmem_range *range, *next;

        mutex_lock(&ashmem_mutex);
        list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned)
                range_del(range);
        mutex_unlock(&ashmem_mutex);

        if (asma->file)
                fput(asma->file);
        kmem_cache_free(ashmem_area_cachep, asma);

        return 0;
}

static ssize_t ashmem_read(struct file *file, char __user *buf,
                           size_t len, loff_t *pos)
{
        struct ashmem_area *asma = file->private_data;
        int ret = 0;

        mutex_lock(&ashmem_mutex);

        /* If size is not set, or set to 0, always return EOF. */
        if (asma->size == 0)
                goto out;

        if (!asma->file) {
                ret = -EBADF;
                goto out;
        }

        ret = asma->file->f_op->read(asma->file, buf, len, pos);
        if (ret < 0)
                goto out;

        /** Update backing file pos, since f_ops->read() doesn't */
        asma->file->f_pos = *pos;

out:
        mutex_unlock(&ashmem_mutex);
        return ret;
}

static loff_t ashmem_llseek(struct file *file, loff_t offset, int origin)
{
        struct ashmem_area *asma = file->private_data;
        int ret;

        mutex_lock(&ashmem_mutex);

        if (asma->size == 0) {
                ret = -EINVAL;
                goto out;
        }

        if (!asma->file) {
                ret = -EBADF;
                goto out;
        }

        ret = asma->file->f_op->llseek(asma->file, offset, origin);
        if (ret < 0)
                goto out;

        /** Copy f_pos from backing file, since f_ops->llseek() sets it */
        file->f_pos = asma->file->f_pos;

out:
        mutex_unlock(&ashmem_mutex);
        return ret;
}

static inline vm_flags_t calc_vm_may_flags(unsigned long prot)
{
        return _calc_vm_trans(prot, PROT_READ,  VM_MAYREAD) |
               _calc_vm_trans(prot, PROT_WRITE, VM_MAYWRITE) |
               _calc_vm_trans(prot, PROT_EXEC,  VM_MAYEXEC);
}

static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct ashmem_area *asma = file->private_data;
        int ret = 0;

        mutex_lock(&ashmem_mutex);

        /* user needs to SET_SIZE before mapping */
        if (unlikely(!asma->size)) {
                ret = -EINVAL;
                goto out;
        }

        /* requested protection bits must match our allowed protection mask */
        if (unlikely((vma->vm_flags & ~calc_vm_prot_bits(asma->prot_mask)) &
                     calc_vm_prot_bits(PROT_MASK))) {
                ret = -EPERM;
                goto out;
        }
        vma->vm_flags &= ~calc_vm_may_flags(~asma->prot_mask);

        if (!asma->file) {
                char *name = ASHMEM_NAME_DEF;
                struct file *vmfile;

                if (asma->name[ASHMEM_NAME_PREFIX_LEN] != '\0')
                        name = asma->name;

                /* ... and allocate the backing shmem file */
                vmfile = shmem_file_setup(name, asma->size, vma->vm_flags);
                if (unlikely(IS_ERR(vmfile))) {
                        ret = PTR_ERR(vmfile);
                        goto out;
                }
                asma->file = vmfile;
        }
        get_file(asma->file);

        /*
         * XXX - Reworked to use shmem_zero_setup() instead of
         * shmem_set_file while we're in staging. -jstultz
         */
        if (vma->vm_flags & VM_SHARED) {
                ret = shmem_zero_setup(vma);
                if (ret) {
                        fput(asma->file);
                        goto out;
                }
        }

        if (vma->vm_file)
                fput(vma->vm_file);
        vma->vm_file = asma->file;

out:
        mutex_unlock(&ashmem_mutex);
        return ret;
}

/*
 * ashmem_shrink - our cache shrinker, called from mm/vmscan.c :: shrink_slab
 *
 * 'nr_to_scan' is the number of objects (pages) to prune, or 0 to query how
 * many objects (pages) we have in total.
 *
 * 'gfp_mask' is the mask of the allocation that got us into this mess.
 *
 * Return value is the number of objects (pages) remaining, or -1 if we cannot
 * proceed without risk of deadlock (due to gfp_mask).
 *
 * We approximate LRU via least-recently-unpinned, jettisoning unpinned partial
 * chunks of ashmem regions LRU-wise one-at-a-time until we hit 'nr_to_scan'
 * pages freed.
 */
static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
{
        struct ashmem_range *range, *next;

        /* We might recurse into filesystem code, so bail out if necessary */
        if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
                return -1;
        if (!sc->nr_to_scan)
                return lru_count;

        mutex_lock(&ashmem_mutex);
        list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
                loff_t start = range->pgstart * PAGE_SIZE;
                loff_t end = (range->pgend + 1) * PAGE_SIZE;

                do_fallocate(range->asma->file,
                                FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                                start, end - start);
                range->purged = ASHMEM_WAS_PURGED;
                lru_del(range);

                sc->nr_to_scan -= range_size(range);
                if (sc->nr_to_scan <= 0)
                        break;
        }
        mutex_unlock(&ashmem_mutex);

        return lru_count;
}

static struct shrinker ashmem_shrinker = {
        .shrink = ashmem_shrink,
        .seeks = DEFAULT_SEEKS * 4,
};

static int set_prot_mask(struct ashmem_area *asma, unsigned long prot)
{
        int ret = 0;

        mutex_lock(&ashmem_mutex);

        /* the user can only remove, not add, protection bits */
        if (unlikely((asma->prot_mask & prot) != prot)) {
                ret = -EINVAL;
                goto out;
        }

        /* does the application expect PROT_READ to imply PROT_EXEC? */
        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
                prot |= PROT_EXEC;

        asma->prot_mask = prot;

out:
        mutex_unlock(&ashmem_mutex);
        return ret;
}

static int set_name(struct ashmem_area *asma, void __user *name)
{
        int ret = 0;
        char local_name[ASHMEM_NAME_LEN];

        /*
         * Holding the ashmem_mutex while doing a copy_from_user might cause
         * an data abort which would try to access mmap_sem. If another
         * thread has invoked ashmem_mmap then it will be holding the
         * semaphore and will be waiting for ashmem_mutex, there by leading to
         * deadlock. We'll release the mutex  and take the name to a local
         * variable that does not need protection and later copy the local
         * variable to the structure member with lock held.
         */
        if (copy_from_user(local_name, name, ASHMEM_NAME_LEN))
                return -EFAULT;

        mutex_lock(&ashmem_mutex);
        /* cannot change an existing mapping's name */
        if (unlikely(asma->file)) {
                ret = -EINVAL;
                goto out;
        }
        memcpy(asma->name + ASHMEM_NAME_PREFIX_LEN,
                local_name, ASHMEM_NAME_LEN);
        asma->name[ASHMEM_FULL_NAME_LEN-1] = '\0';
out:
        mutex_unlock(&ashmem_mutex);

        return ret;
}

static int get_name(struct ashmem_area *asma, void __user *name)
{
        int ret = 0;
        size_t len;
        /*
         * Have a local variable to which we'll copy the content
         * from asma with the lock held. Later we can copy this to the user
         * space safely without holding any locks. So even if we proceed to
         * wait for mmap_sem, it won't lead to deadlock.
         */
        char local_name[ASHMEM_NAME_LEN];

        mutex_lock(&ashmem_mutex);
        if (asma->name[ASHMEM_NAME_PREFIX_LEN] != '\0') {

                /*
                 * Copying only `len', instead of ASHMEM_NAME_LEN, bytes
                 * prevents us from revealing one user's stack to another.
                 */
                len = strlen(asma->name + ASHMEM_NAME_PREFIX_LEN) + 1;
                memcpy(local_name, asma->name + ASHMEM_NAME_PREFIX_LEN, len);
        } else {
                len = sizeof(ASHMEM_NAME_DEF);
                memcpy(local_name, ASHMEM_NAME_DEF, len);
        }
        mutex_unlock(&ashmem_mutex);

        /*
         * Now we are just copying from the stack variable to userland
         * No lock held
         */
        if (unlikely(copy_to_user(name, local_name, len)))
                ret = -EFAULT;
        return ret;
}

/*
 * ashmem_pin - pin the given ashmem region, returning whether it was
 * previously purged (ASHMEM_WAS_PURGED) or not (ASHMEM_NOT_PURGED).
 *
 * Caller must hold ashmem_mutex.
 */
static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
{
        struct ashmem_range *range, *next;
        int ret = ASHMEM_NOT_PURGED;

        list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned) {
                /* moved past last applicable page; we can short circuit */
                if (range_before_page(range, pgstart))
                        break;

                /*
                 * The user can ask us to pin pages that span multiple ranges,
                 * or to pin pages that aren't even unpinned, so this is messy.
                 *
                 * Four cases:
                 * 1. The requested range subsumes an existing range, so we
                 *    just remove the entire matching range.
                 * 2. The requested range overlaps the start of an existing
                 *    range, so we just update that range.
                 * 3. The requested range overlaps the end of an existing
                 *    range, so we just update that range.
                 * 4. The requested range punches a hole in an existing range,
                 *    so we have to update one side of the range and then
                 *    create a new range for the other side.
                 */
                if (page_range_in_range(range, pgstart, pgend)) {
                        ret |= range->purged;

                        /* Case #1: Easy. Just nuke the whole thing. */
                        if (page_range_subsumes_range(range, pgstart, pgend)) {
                                range_del(range);
                                continue;
                        }

                        /* Case #2: We overlap from the start, so adjust it */
                        if (range->pgstart >= pgstart) {
                                range_shrink(range, pgend + 1, range->pgend);
                                continue;
                        }

                        /* Case #3: We overlap from the rear, so adjust it */
                        if (range->pgend <= pgend) {
                                range_shrink(range, range->pgstart, pgstart-1);
                                continue;
                        }

                        /*
                         * Case #4: We eat a chunk out of the middle. A bit
                         * more complicated, we allocate a new range for the
                         * second half and adjust the first chunk's endpoint.
                         */
                        range_alloc(asma, range, range->purged,
                                    pgend + 1, range->pgend);
                        range_shrink(range, range->pgstart, pgstart - 1);
                        break;
                }
        }

        return ret;
}

/*
 * ashmem_unpin - unpin the given range of pages. Returns zero on success.
 *
 * Caller must hold ashmem_mutex.
 */
static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
{
        struct ashmem_range *range, *next;
        unsigned int purged = ASHMEM_NOT_PURGED;

restart:
        list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned) {
                /* short circuit: this is our insertion point */
                if (range_before_page(range, pgstart))
                        break;

                /*
                 * The user can ask us to unpin pages that are already entirely
                 * or partially pinned. We handle those two cases here.
                 */
                if (page_range_subsumed_by_range(range, pgstart, pgend))
                        return 0;
                if (page_range_in_range(range, pgstart, pgend)) {
                        pgstart = min_t(size_t, range->pgstart, pgstart),
                        pgend = max_t(size_t, range->pgend, pgend);
                        purged |= range->purged;
                        range_del(range);
                        goto restart;
                }
        }

        return range_alloc(asma, range, purged, pgstart, pgend);
}

/*
 * ashmem_get_pin_status - Returns ASHMEM_IS_UNPINNED if _any_ pages in the
 * given interval are unpinned and ASHMEM_IS_PINNED otherwise.
 *
 * Caller must hold ashmem_mutex.
 */
static int ashmem_get_pin_status(struct ashmem_area *asma, size_t pgstart,
                                 size_t pgend)
{
        struct ashmem_range *range;
        int ret = ASHMEM_IS_PINNED;

        list_for_each_entry(range, &asma->unpinned_list, unpinned) {
                if (range_before_page(range, pgstart))
                        break;
                if (page_range_in_range(range, pgstart, pgend)) {
                        ret = ASHMEM_IS_UNPINNED;
                        break;
                }
        }

        return ret;
}

static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
                            void __user *p)
{
        struct ashmem_pin pin;
        size_t pgstart, pgend;
        int ret = -EINVAL;

        if (unlikely(!asma->file))
                return -EINVAL;

        if (unlikely(copy_from_user(&pin, p, sizeof(pin))))
                return -EFAULT;

        /* per custom, you can pass zero for len to mean "everything onward" */
        if (!pin.len)
                pin.len = PAGE_ALIGN(asma->size) - pin.offset;

        if (unlikely((pin.offset | pin.len) & ~PAGE_MASK))
                return -EINVAL;

        if (unlikely(((__u32) -1) - pin.offset < pin.len))
                return -EINVAL;

        if (unlikely(PAGE_ALIGN(asma->size) < pin.offset + pin.len))
                return -EINVAL;

        pgstart = pin.offset / PAGE_SIZE;
        pgend = pgstart + (pin.len / PAGE_SIZE) - 1;

        mutex_lock(&ashmem_mutex);

        switch (cmd) {
        case ASHMEM_PIN:
                ret = ashmem_pin(asma, pgstart, pgend);
                break;
        case ASHMEM_UNPIN:
                ret = ashmem_unpin(asma, pgstart, pgend);
                break;
        case ASHMEM_GET_PIN_STATUS:
                ret = ashmem_get_pin_status(asma, pgstart, pgend);
                break;
        }

        mutex_unlock(&ashmem_mutex);

        return ret;
}

static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct ashmem_area *asma = file->private_data;
        long ret = -ENOTTY;

        switch (cmd) {
        case ASHMEM_SET_NAME:
                ret = set_name(asma, (void __user *) arg);
                break;
        case ASHMEM_GET_NAME:
                ret = get_name(asma, (void __user *) arg);
                break;
        case ASHMEM_SET_SIZE:
                ret = -EINVAL;
                if (!asma->file) {
                        ret = 0;
                        asma->size = (size_t) arg;
                }
                break;
        case ASHMEM_GET_SIZE:
                ret = asma->size;
                break;
        case ASHMEM_SET_PROT_MASK:
                ret = set_prot_mask(asma, arg);
                break;
        case ASHMEM_GET_PROT_MASK:
                ret = asma->prot_mask;
                break;
        case ASHMEM_PIN:
        case ASHMEM_UNPIN:
        case ASHMEM_GET_PIN_STATUS:
                ret = ashmem_pin_unpin(asma, cmd, (void __user *) arg);
                break;
        case ASHMEM_PURGE_ALL_CACHES:
                ret = -EPERM;
                if (capable(CAP_SYS_ADMIN)) {
                        struct shrink_control sc = {
                                .gfp_mask = GFP_KERNEL,
                                .nr_to_scan = 0,
                        };
                        ret = ashmem_shrink(&ashmem_shrinker, &sc);
                        sc.nr_to_scan = ret;
                        ashmem_shrink(&ashmem_shrinker, &sc);
                }
                break;
        }

        return ret;
}

/* support of 32bit userspace on 64bit platforms */
#ifdef CONFIG_COMPAT
static long compat_ashmem_ioctl(struct file *file, unsigned int cmd,
                                unsigned long arg)
{

        switch (cmd) {
        case COMPAT_ASHMEM_SET_SIZE:
                cmd = ASHMEM_SET_SIZE;
                break;
        case COMPAT_ASHMEM_SET_PROT_MASK:
                cmd = ASHMEM_SET_PROT_MASK;
                break;
        }
        return ashmem_ioctl(file, cmd, arg);
}
#endif

static const struct file_operations ashmem_fops = {
        .owner = THIS_MODULE,
        .open = ashmem_open,
        .release = ashmem_release,
        .read = ashmem_read,
        .llseek = ashmem_llseek,
        .mmap = ashmem_mmap,
        .unlocked_ioctl = ashmem_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl = compat_ashmem_ioctl,
#endif
};

static struct miscdevice ashmem_misc = {
        .minor = MISC_DYNAMIC_MINOR,
        .name = "ashmem",
        .fops = &ashmem_fops,
};

static int __init ashmem_init(void)
{
        int ret;

        ashmem_area_cachep = kmem_cache_create("ashmem_area_cache",
                                          sizeof(struct ashmem_area),
                                          0, 0, NULL);
        if (unlikely(!ashmem_area_cachep)) {
                pr_err("failed to create slab cache\n");
                return -ENOMEM;
        }

        ashmem_range_cachep = kmem_cache_create("ashmem_range_cache",
                                          sizeof(struct ashmem_range),
                                          0, 0, NULL);
        if (unlikely(!ashmem_range_cachep)) {
                pr_err("failed to create slab cache\n");
                return -ENOMEM;
        }

        ret = misc_register(&ashmem_misc);
        if (unlikely(ret)) {
                pr_err("failed to register misc device!\n");
                return ret;
        }

        register_shrinker(&ashmem_shrinker);

        pr_info("initialized\n");

        return 0;
}

static void __exit ashmem_exit(void)
{
        int ret;

        unregister_shrinker(&ashmem_shrinker);

        ret = misc_deregister(&ashmem_misc);
        if (unlikely(ret))
                pr_err("failed to unregister misc device!\n");

        kmem_cache_destroy(ashmem_range_cachep);
        kmem_cache_destroy(ashmem_area_cachep);

        pr_info("unloaded\n");
}

module_init(ashmem_init);
module_exit(ashmem_exit);

MODULE_LICENSE("GPL");