/* mm/ashmem.c ** ** Anonymous Shared Memory Subsystem, ashmem ** ** Copyright (C) 2008 Google, Inc. ** ** Robert Love ** ** 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. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #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 for /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 = nonseekable_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 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 & ~asma->prot_mask) & PROT_MASK)) { ret = -EPERM; goto out; } 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; } vma->vm_flags |= VM_CAN_NONLINEAR; 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(int nr_to_scan, gfp_t gfp_mask) { struct ashmem_range *range, *next; /* We might recurse into filesystem code, so bail out if necessary */ if (nr_to_scan && !(gfp_mask & __GFP_FS)) return -1; if (!nr_to_scan) return lru_count; /* If our mutex is held, we are recursing into ourselves, so bail out */ if (!mutex_trylock(&ashmem_mutex)) { return -1; } list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) { struct inode *inode = range->asma->file->f_dentry->d_inode; loff_t start = range->pgstart * PAGE_SIZE; loff_t end = (range->pgend + 1) * PAGE_SIZE - 1; vmtruncate_range(inode, start, end); range->purged = ASHMEM_WAS_PURGED; lru_del(range); nr_to_scan -= range_size(range); if (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; mutex_lock(&ashmem_mutex); /* cannot change an existing mapping's name */ if (unlikely(asma->file)) { ret = -EINVAL; goto out; } if (unlikely(copy_from_user(asma->name + ASHMEM_NAME_PREFIX_LEN, name, ASHMEM_NAME_LEN))) ret = -EFAULT; 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; mutex_lock(&ashmem_mutex); if (asma->name[ASHMEM_NAME_PREFIX_LEN] != '\0') { size_t len; /* * 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; if (unlikely(copy_to_user(name, asma->name + ASHMEM_NAME_PREFIX_LEN, len))) ret = -EFAULT; } else { if (unlikely(copy_to_user(name, ASHMEM_NAME_DEF, sizeof(ASHMEM_NAME_DEF)))) ret = -EFAULT; } mutex_unlock(&ashmem_mutex); 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)) { ret = ashmem_shrink(0, GFP_KERNEL); ashmem_shrink(ret, GFP_KERNEL); } break; } return ret; } static struct file_operations ashmem_fops = { .owner = THIS_MODULE, .open = ashmem_open, .release = ashmem_release, .mmap = ashmem_mmap, .unlocked_ioctl = ashmem_ioctl, .compat_ioctl = ashmem_ioctl, }; 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)) { printk(KERN_ERR "ashmem: 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)) { printk(KERN_ERR "ashmem: failed to create slab cache\n"); return -ENOMEM; } ret = misc_register(&ashmem_misc); if (unlikely(ret)) { printk(KERN_ERR "ashmem: failed to register misc device!\n"); return ret; } register_shrinker(&ashmem_shrinker); printk(KERN_INFO "ashmem: initialized\n"); return 0; } static void __exit ashmem_exit(void) { int ret; unregister_shrinker(&ashmem_shrinker); ret = misc_deregister(&ashmem_misc); if (unlikely(ret)) printk(KERN_ERR "ashmem: failed to unregister misc device!\n"); kmem_cache_destroy(ashmem_range_cachep); kmem_cache_destroy(ashmem_area_cachep); printk(KERN_INFO "ashmem: unloaded\n"); } module_init(ashmem_init); module_exit(ashmem_exit); MODULE_LICENSE("GPL");