/* 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_unlock;
if (!asma->file) {
ret = -EBADF;
goto out_unlock;
}
mutex_unlock(&ashmem_mutex);
/*
* asma and asma->file are used outside the lock here. We assume
* once asma->file is set it will never be changed, and will not
* be destroyed until all references to the file are dropped and
* ashmem_release is called.
*/
ret = asma->file->f_op->read(asma->file, buf, len, pos);
if (ret >= 0) {
/** Update backing file pos, since f_ops->read() doesn't */
asma->file->f_pos = *pos;
}
return ret;
out_unlock:
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);
if (vma->vm_flags & VM_SHARED)
shmem_set_file(vma, asma->file);
else {
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;
if (!mutex_trylock(&ashmem_mutex))
return -1;
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;
range->asma->file->f_op->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 len;
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.
*/
len = strncpy_from_user(local_name, name, ASHMEM_NAME_LEN);
if (len < 0)
return len;
if (len == ASHMEM_NAME_LEN)
local_name[ASHMEM_NAME_LEN - 1] = '\0';
mutex_lock(&ashmem_mutex);
/* cannot change an existing mapping's name */
if (unlikely(asma->file))
ret = -EINVAL;
else
strcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name);
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");