/* 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. */ #define pr_fmt(fmt) "ashmem: " fmt #include #include #include #include #include #include #include #include #include #include #include #include #include #include #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) /** * struct ashmem_area - The anonymous shared memory area * @name: The optional name in /proc/pid/maps * @unpinned_list: The list of all ashmem areas * @file: The shmem-based backing file * @size: The size of the mapping, in bytes * @prot_mask: The allowed protection bits, as vm_flags * * The lifecycle of this structure is from our parent file's open() until * its release(). It is also protected by 'ashmem_mutex' * * Warning: Mappings do NOT pin this structure; It dies on close() */ struct ashmem_area { char name[ASHMEM_FULL_NAME_LEN]; struct list_head unpinned_list; struct file *file; size_t size; unsigned long prot_mask; }; /** * struct ashmem_range - A range of unpinned/evictable pages * @lru: The entry in the LRU list * @unpinned: The entry in its area's unpinned list * @asma: The associated anonymous shared memory area. * @pgstart: The starting page (inclusive) * @pgend: The ending page (inclusive) * @purged: The purge status (ASHMEM_NOT or ASHMEM_WAS_PURGED) * * The lifecycle of this structure is from unpin to pin. * It is protected by 'ashmem_mutex' */ struct ashmem_range { struct list_head lru; struct list_head unpinned; struct ashmem_area *asma; size_t pgstart; size_t pgend; unsigned int purged; }; /* LRU list of unpinned pages, protected by ashmem_mutex */ static LIST_HEAD(ashmem_lru_list); /* * long lru_count - The count of pages on our LRU list. * * This is 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; static inline unsigned long range_size(struct ashmem_range *range) { return range->pgend - range->pgstart + 1; } static inline bool range_on_lru(struct ashmem_range *range) { return range->purged == ASHMEM_NOT_PURGED; } static inline bool page_range_subsumes_range(struct ashmem_range *range, size_t start, size_t end) { return (range->pgstart >= start) && (range->pgend <= end); } static inline bool page_range_subsumed_by_range(struct ashmem_range *range, size_t start, size_t end) { return (range->pgstart <= start) && (range->pgend >= end); } static inline bool page_in_range(struct ashmem_range *range, size_t page) { return (range->pgstart <= page) && (range->pgend >= page); } static inline bool page_range_in_range(struct ashmem_range *range, size_t start, size_t end) { return page_in_range(range, start) || page_in_range(range, end) || page_range_subsumes_range(range, start, end); } static inline bool range_before_page(struct ashmem_range *range, size_t page) { return range->pgend < page; } #define PROT_MASK (PROT_EXEC | PROT_READ | PROT_WRITE) /** * lru_add() - Adds a range of memory to the LRU list * @range: The memory range being added. * * The range is first added to the end (tail) of the LRU list. * After this, the size of the range is added to @lru_count */ static inline void lru_add(struct ashmem_range *range) { list_add_tail(&range->lru, &ashmem_lru_list); lru_count += range_size(range); } /** * lru_del() - Removes a range of memory from the LRU list * @range: The memory range being removed * * The range is first deleted from the LRU list. * After this, the size of the range is removed from @lru_count */ static inline void lru_del(struct ashmem_range *range) { list_del(&range->lru); lru_count -= range_size(range); } /** * range_alloc() - Allocates and initializes a new ashmem_range structure * @asma: The associated ashmem_area * @prev_range: The previous ashmem_range in the sorted asma->unpinned list * @purged: Initial purge status (ASMEM_NOT_PURGED or ASHMEM_WAS_PURGED) * @start: The starting page (inclusive) * @end: The ending page (inclusive) * * This function is protected by ashmem_mutex. * * Return: 0 if successful, or -ENOMEM if there is an error */ 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; } /** * range_del() - Deletes and dealloctes an ashmem_range structure * @range: The associated ashmem_range that has previously been allocated */ 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 an ashmem_range * @range: The associated ashmem_range being shrunk * @start: The starting byte of the new range * @end: The ending byte of the new range * * This does not modify the data inside the existing range in any way - It * simply shrinks the boundaries of the range. * * Theoretically, with a little tweaking, this could eventually be changed * to range_resize, and expand the lru_count if the new range is larger. */ 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); } /** * ashmem_open() - Opens an Anonymous Shared Memory structure * @inode: The backing file's index node(?) * @file: The backing file * * Please note that the ashmem_area is not returned by this function - It is * instead written to "file->private_data". * * Return: 0 if successful, or another code if unsuccessful. */ 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; } /** * ashmem_release() - Releases an Anonymous Shared Memory structure * @ignored: The backing file's Index Node(?) - It is ignored here. * @file: The backing file * * Return: 0 if successful. If it is anything else, go have a coffee and * try again. */ 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_iter(struct kiocb *iocb, struct iov_iter *iter) { struct ashmem_area *asma = iocb->ki_filp->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; } /* * 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. */ mutex_unlock(&ashmem_mutex); ret = vfs_iter_read(asma->file, iter, &iocb->ki_pos, 0); mutex_lock(&ashmem_mutex); if (ret > 0) asma->file->f_pos = iocb->ki_pos; 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 = vfs_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, 0)) & calc_vm_prot_bits(PROT_MASK, 0))) { 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 (IS_ERR(vmfile)) { ret = PTR_ERR(vmfile); goto out; } vmfile->f_mode |= FMODE_LSEEK; 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 * * 'nr_to_scan' is the number of objects to scan for freeing. * * 'gfp_mask' is the mask of the allocation that got us into this mess. * * Return value is the number of objects freed 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 unsigned long ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) { struct ashmem_range *range, *next; unsigned long freed = 0; /* We might recurse into filesystem code, so bail out if necessary */ if (!(sc->gfp_mask & __GFP_FS)) return SHRINK_STOP; 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; vfs_fallocate(range->asma->file, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, start, end - start); range->purged = ASHMEM_WAS_PURGED; lru_del(range); freed += range_size(range); if (--sc->nr_to_scan <= 0) break; } mutex_unlock(&ashmem_mutex); return freed; } static unsigned long ashmem_shrink_count(struct shrinker *shrink, struct shrink_control *sc) { /* * note that lru_count is count of pages on the lru, not a count of * objects on the list. This means the scan function needs to return the * number of pages freed, not the number of objects scanned. */ return lru_count; } static struct shrinker ashmem_shrinker = { .count_objects = ashmem_shrink_count, .scan_objects = ashmem_shrink_scan, /* * XXX (dchinner): I wish people would comment on why they need on * significant changes to the default value here */ .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(range->pgstart, pgstart); pgend = max(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 = LONG_MAX, }; ret = ashmem_shrink_count(&ashmem_shrinker, &sc); ashmem_shrink_scan(&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_iter = ashmem_read_iter, .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 = -ENOMEM; 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"); goto out; } 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"); goto out_free1; } ret = misc_register(&ashmem_misc); if (unlikely(ret)) { pr_err("failed to register misc device!\n"); goto out_free2; } register_shrinker(&ashmem_shrinker); pr_info("initialized\n"); return 0; out_free2: kmem_cache_destroy(ashmem_range_cachep); out_free1: kmem_cache_destroy(ashmem_area_cachep); out: return ret; } device_initcall(ashmem_init);