| /* |
| * fs/userfaultfd.c |
| * |
| * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> |
| * Copyright (C) 2008-2009 Red Hat, Inc. |
| * Copyright (C) 2015 Red Hat, Inc. |
| * |
| * This work is licensed under the terms of the GNU GPL, version 2. See |
| * the COPYING file in the top-level directory. |
| * |
| * Some part derived from fs/eventfd.c (anon inode setup) and |
| * mm/ksm.c (mm hashing). |
| */ |
| |
| #include <linux/hashtable.h> |
| #include <linux/sched.h> |
| #include <linux/mm.h> |
| #include <linux/poll.h> |
| #include <linux/slab.h> |
| #include <linux/seq_file.h> |
| #include <linux/file.h> |
| #include <linux/bug.h> |
| #include <linux/anon_inodes.h> |
| #include <linux/syscalls.h> |
| #include <linux/userfaultfd_k.h> |
| #include <linux/mempolicy.h> |
| #include <linux/ioctl.h> |
| #include <linux/security.h> |
| |
| enum userfaultfd_state { |
| UFFD_STATE_WAIT_API, |
| UFFD_STATE_RUNNING, |
| }; |
| |
| struct userfaultfd_ctx { |
| /* pseudo fd refcounting */ |
| atomic_t refcount; |
| /* waitqueue head for the pending (i.e. not read) userfaults */ |
| wait_queue_head_t fault_pending_wqh; |
| /* waitqueue head for the userfaults */ |
| wait_queue_head_t fault_wqh; |
| /* waitqueue head for the pseudo fd to wakeup poll/read */ |
| wait_queue_head_t fd_wqh; |
| /* userfaultfd syscall flags */ |
| unsigned int flags; |
| /* state machine */ |
| enum userfaultfd_state state; |
| /* released */ |
| bool released; |
| /* mm with one ore more vmas attached to this userfaultfd_ctx */ |
| struct mm_struct *mm; |
| }; |
| |
| struct userfaultfd_wait_queue { |
| struct uffd_msg msg; |
| wait_queue_t wq; |
| struct userfaultfd_ctx *ctx; |
| }; |
| |
| struct userfaultfd_wake_range { |
| unsigned long start; |
| unsigned long len; |
| }; |
| |
| static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode, |
| int wake_flags, void *key) |
| { |
| struct userfaultfd_wake_range *range = key; |
| int ret; |
| struct userfaultfd_wait_queue *uwq; |
| unsigned long start, len; |
| |
| uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| ret = 0; |
| /* len == 0 means wake all */ |
| start = range->start; |
| len = range->len; |
| if (len && (start > uwq->msg.arg.pagefault.address || |
| start + len <= uwq->msg.arg.pagefault.address)) |
| goto out; |
| ret = wake_up_state(wq->private, mode); |
| if (ret) |
| /* |
| * Wake only once, autoremove behavior. |
| * |
| * After the effect of list_del_init is visible to the |
| * other CPUs, the waitqueue may disappear from under |
| * us, see the !list_empty_careful() in |
| * handle_userfault(). try_to_wake_up() has an |
| * implicit smp_mb__before_spinlock, and the |
| * wq->private is read before calling the extern |
| * function "wake_up_state" (which in turns calls |
| * try_to_wake_up). While the spin_lock;spin_unlock; |
| * wouldn't be enough, the smp_mb__before_spinlock is |
| * enough to avoid an explicit smp_mb() here. |
| */ |
| list_del_init(&wq->task_list); |
| out: |
| return ret; |
| } |
| |
| /** |
| * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd |
| * context. |
| * @ctx: [in] Pointer to the userfaultfd context. |
| * |
| * Returns: In case of success, returns not zero. |
| */ |
| static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) |
| { |
| if (!atomic_inc_not_zero(&ctx->refcount)) |
| BUG(); |
| } |
| |
| /** |
| * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd |
| * context. |
| * @ctx: [in] Pointer to userfaultfd context. |
| * |
| * The userfaultfd context reference must have been previously acquired either |
| * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget(). |
| */ |
| static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) |
| { |
| if (atomic_dec_and_test(&ctx->refcount)) { |
| VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock)); |
| VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh)); |
| VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock)); |
| VM_BUG_ON(waitqueue_active(&ctx->fault_wqh)); |
| VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock)); |
| VM_BUG_ON(waitqueue_active(&ctx->fd_wqh)); |
| mmput(ctx->mm); |
| kfree(ctx); |
| } |
| } |
| |
| static inline void msg_init(struct uffd_msg *msg) |
| { |
| BUILD_BUG_ON(sizeof(struct uffd_msg) != 32); |
| /* |
| * Must use memset to zero out the paddings or kernel data is |
| * leaked to userland. |
| */ |
| memset(msg, 0, sizeof(struct uffd_msg)); |
| } |
| |
| static inline struct uffd_msg userfault_msg(unsigned long address, |
| unsigned int flags, |
| unsigned long reason) |
| { |
| struct uffd_msg msg; |
| msg_init(&msg); |
| msg.event = UFFD_EVENT_PAGEFAULT; |
| msg.arg.pagefault.address = address; |
| if (flags & FAULT_FLAG_WRITE) |
| /* |
| * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the |
| * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE |
| * was not set in a UFFD_EVENT_PAGEFAULT, it means it |
| * was a read fault, otherwise if set it means it's |
| * a write fault. |
| */ |
| msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE; |
| if (reason & VM_UFFD_WP) |
| /* |
| * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the |
| * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was |
| * not set in a UFFD_EVENT_PAGEFAULT, it means it was |
| * a missing fault, otherwise if set it means it's a |
| * write protect fault. |
| */ |
| msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP; |
| return msg; |
| } |
| |
| /* |
| * The locking rules involved in returning VM_FAULT_RETRY depending on |
| * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and |
| * FAULT_FLAG_KILLABLE are not straightforward. The "Caution" |
| * recommendation in __lock_page_or_retry is not an understatement. |
| * |
| * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released |
| * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is |
| * not set. |
| * |
| * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not |
| * set, VM_FAULT_RETRY can still be returned if and only if there are |
| * fatal_signal_pending()s, and the mmap_sem must be released before |
| * returning it. |
| */ |
| int handle_userfault(struct vm_area_struct *vma, unsigned long address, |
| unsigned int flags, unsigned long reason) |
| { |
| struct mm_struct *mm = vma->vm_mm; |
| struct userfaultfd_ctx *ctx; |
| struct userfaultfd_wait_queue uwq; |
| int ret; |
| |
| BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); |
| |
| ret = VM_FAULT_SIGBUS; |
| ctx = vma->vm_userfaultfd_ctx.ctx; |
| if (!ctx) |
| goto out; |
| |
| BUG_ON(ctx->mm != mm); |
| |
| VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP)); |
| VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP)); |
| |
| /* |
| * If it's already released don't get it. This avoids to loop |
| * in __get_user_pages if userfaultfd_release waits on the |
| * caller of handle_userfault to release the mmap_sem. |
| */ |
| if (unlikely(ACCESS_ONCE(ctx->released))) |
| goto out; |
| |
| /* |
| * Check that we can return VM_FAULT_RETRY. |
| * |
| * NOTE: it should become possible to return VM_FAULT_RETRY |
| * even if FAULT_FLAG_TRIED is set without leading to gup() |
| * -EBUSY failures, if the userfaultfd is to be extended for |
| * VM_UFFD_WP tracking and we intend to arm the userfault |
| * without first stopping userland access to the memory. For |
| * VM_UFFD_MISSING userfaults this is enough for now. |
| */ |
| if (unlikely(!(flags & FAULT_FLAG_ALLOW_RETRY))) { |
| /* |
| * Validate the invariant that nowait must allow retry |
| * to be sure not to return SIGBUS erroneously on |
| * nowait invocations. |
| */ |
| BUG_ON(flags & FAULT_FLAG_RETRY_NOWAIT); |
| #ifdef CONFIG_DEBUG_VM |
| if (printk_ratelimit()) { |
| printk(KERN_WARNING |
| "FAULT_FLAG_ALLOW_RETRY missing %x\n", flags); |
| dump_stack(); |
| } |
| #endif |
| goto out; |
| } |
| |
| /* |
| * Handle nowait, not much to do other than tell it to retry |
| * and wait. |
| */ |
| ret = VM_FAULT_RETRY; |
| if (flags & FAULT_FLAG_RETRY_NOWAIT) |
| goto out; |
| |
| /* take the reference before dropping the mmap_sem */ |
| userfaultfd_ctx_get(ctx); |
| |
| /* be gentle and immediately relinquish the mmap_sem */ |
| up_read(&mm->mmap_sem); |
| |
| init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); |
| uwq.wq.private = current; |
| uwq.msg = userfault_msg(address, flags, reason); |
| uwq.ctx = ctx; |
| |
| spin_lock(&ctx->fault_pending_wqh.lock); |
| /* |
| * After the __add_wait_queue the uwq is visible to userland |
| * through poll/read(). |
| */ |
| __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq); |
| /* |
| * The smp_mb() after __set_current_state prevents the reads |
| * following the spin_unlock to happen before the list_add in |
| * __add_wait_queue. |
| */ |
| set_current_state(TASK_KILLABLE); |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| |
| if (likely(!ACCESS_ONCE(ctx->released) && |
| !fatal_signal_pending(current))) { |
| wake_up_poll(&ctx->fd_wqh, POLLIN); |
| schedule(); |
| ret |= VM_FAULT_MAJOR; |
| } |
| |
| __set_current_state(TASK_RUNNING); |
| |
| /* |
| * Here we race with the list_del; list_add in |
| * userfaultfd_ctx_read(), however because we don't ever run |
| * list_del_init() to refile across the two lists, the prev |
| * and next pointers will never point to self. list_add also |
| * would never let any of the two pointers to point to |
| * self. So list_empty_careful won't risk to see both pointers |
| * pointing to self at any time during the list refile. The |
| * only case where list_del_init() is called is the full |
| * removal in the wake function and there we don't re-list_add |
| * and it's fine not to block on the spinlock. The uwq on this |
| * kernel stack can be released after the list_del_init. |
| */ |
| if (!list_empty_careful(&uwq.wq.task_list)) { |
| spin_lock(&ctx->fault_pending_wqh.lock); |
| /* |
| * No need of list_del_init(), the uwq on the stack |
| * will be freed shortly anyway. |
| */ |
| list_del(&uwq.wq.task_list); |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| } |
| |
| /* |
| * ctx may go away after this if the userfault pseudo fd is |
| * already released. |
| */ |
| userfaultfd_ctx_put(ctx); |
| |
| out: |
| return ret; |
| } |
| |
| static int userfaultfd_release(struct inode *inode, struct file *file) |
| { |
| struct userfaultfd_ctx *ctx = file->private_data; |
| struct mm_struct *mm = ctx->mm; |
| struct vm_area_struct *vma, *prev; |
| /* len == 0 means wake all */ |
| struct userfaultfd_wake_range range = { .len = 0, }; |
| unsigned long new_flags; |
| |
| ACCESS_ONCE(ctx->released) = true; |
| |
| /* |
| * Flush page faults out of all CPUs. NOTE: all page faults |
| * must be retried without returning VM_FAULT_SIGBUS if |
| * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx |
| * changes while handle_userfault released the mmap_sem. So |
| * it's critical that released is set to true (above), before |
| * taking the mmap_sem for writing. |
| */ |
| down_write(&mm->mmap_sem); |
| prev = NULL; |
| for (vma = mm->mmap; vma; vma = vma->vm_next) { |
| cond_resched(); |
| BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ |
| !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); |
| if (vma->vm_userfaultfd_ctx.ctx != ctx) { |
| prev = vma; |
| continue; |
| } |
| new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); |
| prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, |
| new_flags, vma->anon_vma, |
| vma->vm_file, vma->vm_pgoff, |
| vma_policy(vma), |
| NULL_VM_UFFD_CTX); |
| if (prev) |
| vma = prev; |
| else |
| prev = vma; |
| vma->vm_flags = new_flags; |
| vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; |
| } |
| up_write(&mm->mmap_sem); |
| |
| /* |
| * After no new page faults can wait on this fault_*wqh, flush |
| * the last page faults that may have been already waiting on |
| * the fault_*wqh. |
| */ |
| spin_lock(&ctx->fault_pending_wqh.lock); |
| __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, 0, &range); |
| __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, 0, &range); |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| |
| wake_up_poll(&ctx->fd_wqh, POLLHUP); |
| userfaultfd_ctx_put(ctx); |
| return 0; |
| } |
| |
| /* fault_pending_wqh.lock must be hold by the caller */ |
| static inline struct userfaultfd_wait_queue *find_userfault( |
| struct userfaultfd_ctx *ctx) |
| { |
| wait_queue_t *wq; |
| struct userfaultfd_wait_queue *uwq; |
| |
| VM_BUG_ON(!spin_is_locked(&ctx->fault_pending_wqh.lock)); |
| |
| uwq = NULL; |
| if (!waitqueue_active(&ctx->fault_pending_wqh)) |
| goto out; |
| /* walk in reverse to provide FIFO behavior to read userfaults */ |
| wq = list_last_entry(&ctx->fault_pending_wqh.task_list, |
| typeof(*wq), task_list); |
| uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| out: |
| return uwq; |
| } |
| |
| static unsigned int userfaultfd_poll(struct file *file, poll_table *wait) |
| { |
| struct userfaultfd_ctx *ctx = file->private_data; |
| unsigned int ret; |
| |
| poll_wait(file, &ctx->fd_wqh, wait); |
| |
| switch (ctx->state) { |
| case UFFD_STATE_WAIT_API: |
| return POLLERR; |
| case UFFD_STATE_RUNNING: |
| /* |
| * poll() never guarantees that read won't block. |
| * userfaults can be waken before they're read(). |
| */ |
| if (unlikely(!(file->f_flags & O_NONBLOCK))) |
| return POLLERR; |
| /* |
| * lockless access to see if there are pending faults |
| * __pollwait last action is the add_wait_queue but |
| * the spin_unlock would allow the waitqueue_active to |
| * pass above the actual list_add inside |
| * add_wait_queue critical section. So use a full |
| * memory barrier to serialize the list_add write of |
| * add_wait_queue() with the waitqueue_active read |
| * below. |
| */ |
| ret = 0; |
| smp_mb(); |
| if (waitqueue_active(&ctx->fault_pending_wqh)) |
| ret = POLLIN; |
| return ret; |
| default: |
| BUG(); |
| } |
| } |
| |
| static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, |
| struct uffd_msg *msg) |
| { |
| ssize_t ret; |
| DECLARE_WAITQUEUE(wait, current); |
| struct userfaultfd_wait_queue *uwq; |
| |
| /* always take the fd_wqh lock before the fault_pending_wqh lock */ |
| spin_lock(&ctx->fd_wqh.lock); |
| __add_wait_queue(&ctx->fd_wqh, &wait); |
| for (;;) { |
| set_current_state(TASK_INTERRUPTIBLE); |
| spin_lock(&ctx->fault_pending_wqh.lock); |
| uwq = find_userfault(ctx); |
| if (uwq) { |
| /* |
| * The fault_pending_wqh.lock prevents the uwq |
| * to disappear from under us. |
| * |
| * Refile this userfault from |
| * fault_pending_wqh to fault_wqh, it's not |
| * pending anymore after we read it. |
| * |
| * Use list_del() by hand (as |
| * userfaultfd_wake_function also uses |
| * list_del_init() by hand) to be sure nobody |
| * changes __remove_wait_queue() to use |
| * list_del_init() in turn breaking the |
| * !list_empty_careful() check in |
| * handle_userfault(). The uwq->wq.task_list |
| * must never be empty at any time during the |
| * refile, or the waitqueue could disappear |
| * from under us. The "wait_queue_head_t" |
| * parameter of __remove_wait_queue() is unused |
| * anyway. |
| */ |
| list_del(&uwq->wq.task_list); |
| __add_wait_queue(&ctx->fault_wqh, &uwq->wq); |
| |
| /* careful to always initialize msg if ret == 0 */ |
| *msg = uwq->msg; |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| ret = 0; |
| break; |
| } |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| if (signal_pending(current)) { |
| ret = -ERESTARTSYS; |
| break; |
| } |
| if (no_wait) { |
| ret = -EAGAIN; |
| break; |
| } |
| spin_unlock(&ctx->fd_wqh.lock); |
| schedule(); |
| spin_lock(&ctx->fd_wqh.lock); |
| } |
| __remove_wait_queue(&ctx->fd_wqh, &wait); |
| __set_current_state(TASK_RUNNING); |
| spin_unlock(&ctx->fd_wqh.lock); |
| |
| return ret; |
| } |
| |
| static ssize_t userfaultfd_read(struct file *file, char __user *buf, |
| size_t count, loff_t *ppos) |
| { |
| struct userfaultfd_ctx *ctx = file->private_data; |
| ssize_t _ret, ret = 0; |
| struct uffd_msg msg; |
| int no_wait = file->f_flags & O_NONBLOCK; |
| |
| if (ctx->state == UFFD_STATE_WAIT_API) |
| return -EINVAL; |
| BUG_ON(ctx->state != UFFD_STATE_RUNNING); |
| |
| for (;;) { |
| if (count < sizeof(msg)) |
| return ret ? ret : -EINVAL; |
| _ret = userfaultfd_ctx_read(ctx, no_wait, &msg); |
| if (_ret < 0) |
| return ret ? ret : _ret; |
| if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg))) |
| return ret ? ret : -EFAULT; |
| ret += sizeof(msg); |
| buf += sizeof(msg); |
| count -= sizeof(msg); |
| /* |
| * Allow to read more than one fault at time but only |
| * block if waiting for the very first one. |
| */ |
| no_wait = O_NONBLOCK; |
| } |
| } |
| |
| static void __wake_userfault(struct userfaultfd_ctx *ctx, |
| struct userfaultfd_wake_range *range) |
| { |
| unsigned long start, end; |
| |
| start = range->start; |
| end = range->start + range->len; |
| |
| spin_lock(&ctx->fault_pending_wqh.lock); |
| /* wake all in the range and autoremove */ |
| if (waitqueue_active(&ctx->fault_pending_wqh)) |
| __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, 0, |
| range); |
| if (waitqueue_active(&ctx->fault_wqh)) |
| __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, 0, range); |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| } |
| |
| static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, |
| struct userfaultfd_wake_range *range) |
| { |
| /* |
| * To be sure waitqueue_active() is not reordered by the CPU |
| * before the pagetable update, use an explicit SMP memory |
| * barrier here. PT lock release or up_read(mmap_sem) still |
| * have release semantics that can allow the |
| * waitqueue_active() to be reordered before the pte update. |
| */ |
| smp_mb(); |
| |
| /* |
| * Use waitqueue_active because it's very frequent to |
| * change the address space atomically even if there are no |
| * userfaults yet. So we take the spinlock only when we're |
| * sure we've userfaults to wake. |
| */ |
| if (waitqueue_active(&ctx->fault_pending_wqh) || |
| waitqueue_active(&ctx->fault_wqh)) |
| __wake_userfault(ctx, range); |
| } |
| |
| static __always_inline int validate_range(struct mm_struct *mm, |
| __u64 start, __u64 len) |
| { |
| __u64 task_size = mm->task_size; |
| |
| if (start & ~PAGE_MASK) |
| return -EINVAL; |
| if (len & ~PAGE_MASK) |
| return -EINVAL; |
| if (!len) |
| return -EINVAL; |
| if (start < mmap_min_addr) |
| return -EINVAL; |
| if (start >= task_size) |
| return -EINVAL; |
| if (len > task_size - start) |
| return -EINVAL; |
| return 0; |
| } |
| |
| static int userfaultfd_register(struct userfaultfd_ctx *ctx, |
| unsigned long arg) |
| { |
| struct mm_struct *mm = ctx->mm; |
| struct vm_area_struct *vma, *prev, *cur; |
| int ret; |
| struct uffdio_register uffdio_register; |
| struct uffdio_register __user *user_uffdio_register; |
| unsigned long vm_flags, new_flags; |
| bool found; |
| unsigned long start, end, vma_end; |
| |
| user_uffdio_register = (struct uffdio_register __user *) arg; |
| |
| ret = -EFAULT; |
| if (copy_from_user(&uffdio_register, user_uffdio_register, |
| sizeof(uffdio_register)-sizeof(__u64))) |
| goto out; |
| |
| ret = -EINVAL; |
| if (!uffdio_register.mode) |
| goto out; |
| if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING| |
| UFFDIO_REGISTER_MODE_WP)) |
| goto out; |
| vm_flags = 0; |
| if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) |
| vm_flags |= VM_UFFD_MISSING; |
| if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { |
| vm_flags |= VM_UFFD_WP; |
| /* |
| * FIXME: remove the below error constraint by |
| * implementing the wprotect tracking mode. |
| */ |
| ret = -EINVAL; |
| goto out; |
| } |
| |
| ret = validate_range(mm, uffdio_register.range.start, |
| uffdio_register.range.len); |
| if (ret) |
| goto out; |
| |
| start = uffdio_register.range.start; |
| end = start + uffdio_register.range.len; |
| |
| down_write(&mm->mmap_sem); |
| vma = find_vma_prev(mm, start, &prev); |
| |
| ret = -ENOMEM; |
| if (!vma) |
| goto out_unlock; |
| |
| /* check that there's at least one vma in the range */ |
| ret = -EINVAL; |
| if (vma->vm_start >= end) |
| goto out_unlock; |
| |
| /* |
| * Search for not compatible vmas. |
| * |
| * FIXME: this shall be relaxed later so that it doesn't fail |
| * on tmpfs backed vmas (in addition to the current allowance |
| * on anonymous vmas). |
| */ |
| found = false; |
| for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { |
| cond_resched(); |
| |
| BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ |
| !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); |
| |
| /* check not compatible vmas */ |
| ret = -EINVAL; |
| if (cur->vm_ops) |
| goto out_unlock; |
| |
| /* |
| * Check that this vma isn't already owned by a |
| * different userfaultfd. We can't allow more than one |
| * userfaultfd to own a single vma simultaneously or we |
| * wouldn't know which one to deliver the userfaults to. |
| */ |
| ret = -EBUSY; |
| if (cur->vm_userfaultfd_ctx.ctx && |
| cur->vm_userfaultfd_ctx.ctx != ctx) |
| goto out_unlock; |
| |
| found = true; |
| } |
| BUG_ON(!found); |
| |
| if (vma->vm_start < start) |
| prev = vma; |
| |
| ret = 0; |
| do { |
| cond_resched(); |
| |
| BUG_ON(vma->vm_ops); |
| BUG_ON(vma->vm_userfaultfd_ctx.ctx && |
| vma->vm_userfaultfd_ctx.ctx != ctx); |
| |
| /* |
| * Nothing to do: this vma is already registered into this |
| * userfaultfd and with the right tracking mode too. |
| */ |
| if (vma->vm_userfaultfd_ctx.ctx == ctx && |
| (vma->vm_flags & vm_flags) == vm_flags) |
| goto skip; |
| |
| if (vma->vm_start > start) |
| start = vma->vm_start; |
| vma_end = min(end, vma->vm_end); |
| |
| new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; |
| prev = vma_merge(mm, prev, start, vma_end, new_flags, |
| vma->anon_vma, vma->vm_file, vma->vm_pgoff, |
| vma_policy(vma), |
| ((struct vm_userfaultfd_ctx){ ctx })); |
| if (prev) { |
| vma = prev; |
| goto next; |
| } |
| if (vma->vm_start < start) { |
| ret = split_vma(mm, vma, start, 1); |
| if (ret) |
| break; |
| } |
| if (vma->vm_end > end) { |
| ret = split_vma(mm, vma, end, 0); |
| if (ret) |
| break; |
| } |
| next: |
| /* |
| * In the vma_merge() successful mprotect-like case 8: |
| * the next vma was merged into the current one and |
| * the current one has not been updated yet. |
| */ |
| vma->vm_flags = new_flags; |
| vma->vm_userfaultfd_ctx.ctx = ctx; |
| |
| skip: |
| prev = vma; |
| start = vma->vm_end; |
| vma = vma->vm_next; |
| } while (vma && vma->vm_start < end); |
| out_unlock: |
| up_write(&mm->mmap_sem); |
| if (!ret) { |
| /* |
| * Now that we scanned all vmas we can already tell |
| * userland which ioctls methods are guaranteed to |
| * succeed on this range. |
| */ |
| if (put_user(UFFD_API_RANGE_IOCTLS, |
| &user_uffdio_register->ioctls)) |
| ret = -EFAULT; |
| } |
| out: |
| return ret; |
| } |
| |
| static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, |
| unsigned long arg) |
| { |
| struct mm_struct *mm = ctx->mm; |
| struct vm_area_struct *vma, *prev, *cur; |
| int ret; |
| struct uffdio_range uffdio_unregister; |
| unsigned long new_flags; |
| bool found; |
| unsigned long start, end, vma_end; |
| const void __user *buf = (void __user *)arg; |
| |
| ret = -EFAULT; |
| if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) |
| goto out; |
| |
| ret = validate_range(mm, uffdio_unregister.start, |
| uffdio_unregister.len); |
| if (ret) |
| goto out; |
| |
| start = uffdio_unregister.start; |
| end = start + uffdio_unregister.len; |
| |
| down_write(&mm->mmap_sem); |
| vma = find_vma_prev(mm, start, &prev); |
| |
| ret = -ENOMEM; |
| if (!vma) |
| goto out_unlock; |
| |
| /* check that there's at least one vma in the range */ |
| ret = -EINVAL; |
| if (vma->vm_start >= end) |
| goto out_unlock; |
| |
| /* |
| * Search for not compatible vmas. |
| * |
| * FIXME: this shall be relaxed later so that it doesn't fail |
| * on tmpfs backed vmas (in addition to the current allowance |
| * on anonymous vmas). |
| */ |
| found = false; |
| ret = -EINVAL; |
| for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { |
| cond_resched(); |
| |
| BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ |
| !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); |
| |
| /* |
| * Check not compatible vmas, not strictly required |
| * here as not compatible vmas cannot have an |
| * userfaultfd_ctx registered on them, but this |
| * provides for more strict behavior to notice |
| * unregistration errors. |
| */ |
| if (cur->vm_ops) |
| goto out_unlock; |
| |
| found = true; |
| } |
| BUG_ON(!found); |
| |
| if (vma->vm_start < start) |
| prev = vma; |
| |
| ret = 0; |
| do { |
| cond_resched(); |
| |
| BUG_ON(vma->vm_ops); |
| |
| /* |
| * Nothing to do: this vma is already registered into this |
| * userfaultfd and with the right tracking mode too. |
| */ |
| if (!vma->vm_userfaultfd_ctx.ctx) |
| goto skip; |
| |
| if (vma->vm_start > start) |
| start = vma->vm_start; |
| vma_end = min(end, vma->vm_end); |
| |
| new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); |
| prev = vma_merge(mm, prev, start, vma_end, new_flags, |
| vma->anon_vma, vma->vm_file, vma->vm_pgoff, |
| vma_policy(vma), |
| NULL_VM_UFFD_CTX); |
| if (prev) { |
| vma = prev; |
| goto next; |
| } |
| if (vma->vm_start < start) { |
| ret = split_vma(mm, vma, start, 1); |
| if (ret) |
| break; |
| } |
| if (vma->vm_end > end) { |
| ret = split_vma(mm, vma, end, 0); |
| if (ret) |
| break; |
| } |
| next: |
| /* |
| * In the vma_merge() successful mprotect-like case 8: |
| * the next vma was merged into the current one and |
| * the current one has not been updated yet. |
| */ |
| vma->vm_flags = new_flags; |
| vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; |
| |
| skip: |
| prev = vma; |
| start = vma->vm_end; |
| vma = vma->vm_next; |
| } while (vma && vma->vm_start < end); |
| out_unlock: |
| up_write(&mm->mmap_sem); |
| out: |
| return ret; |
| } |
| |
| /* |
| * userfaultfd_wake is needed in case an userfault is in flight by the |
| * time a UFFDIO_COPY (or other ioctl variants) completes. The page |
| * may be well get mapped and the page fault if repeated wouldn't lead |
| * to a userfault anymore, but before scheduling in TASK_KILLABLE mode |
| * handle_userfault() doesn't recheck the pagetables and it doesn't |
| * serialize against UFFDO_COPY (or other ioctl variants). Ultimately |
| * the knowledge of which pages are mapped is left to userland who is |
| * responsible for handling the race between read() userfaults and |
| * background UFFDIO_COPY (or other ioctl variants), if done by |
| * separate concurrent threads. |
| * |
| * userfaultfd_wake may be used in combination with the |
| * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches. |
| */ |
| static int userfaultfd_wake(struct userfaultfd_ctx *ctx, |
| unsigned long arg) |
| { |
| int ret; |
| struct uffdio_range uffdio_wake; |
| struct userfaultfd_wake_range range; |
| const void __user *buf = (void __user *)arg; |
| |
| ret = -EFAULT; |
| if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) |
| goto out; |
| |
| ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); |
| if (ret) |
| goto out; |
| |
| range.start = uffdio_wake.start; |
| range.len = uffdio_wake.len; |
| |
| /* |
| * len == 0 means wake all and we don't want to wake all here, |
| * so check it again to be sure. |
| */ |
| VM_BUG_ON(!range.len); |
| |
| wake_userfault(ctx, &range); |
| ret = 0; |
| |
| out: |
| return ret; |
| } |
| |
| /* |
| * userland asks for a certain API version and we return which bits |
| * and ioctl commands are implemented in this kernel for such API |
| * version or -EINVAL if unknown. |
| */ |
| static int userfaultfd_api(struct userfaultfd_ctx *ctx, |
| unsigned long arg) |
| { |
| struct uffdio_api uffdio_api; |
| void __user *buf = (void __user *)arg; |
| int ret; |
| |
| ret = -EINVAL; |
| if (ctx->state != UFFD_STATE_WAIT_API) |
| goto out; |
| ret = -EFAULT; |
| if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) |
| goto out; |
| if (uffdio_api.api != UFFD_API || uffdio_api.features) { |
| memset(&uffdio_api, 0, sizeof(uffdio_api)); |
| if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) |
| goto out; |
| ret = -EINVAL; |
| goto out; |
| } |
| uffdio_api.features = UFFD_API_FEATURES; |
| uffdio_api.ioctls = UFFD_API_IOCTLS; |
| ret = -EFAULT; |
| if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) |
| goto out; |
| ctx->state = UFFD_STATE_RUNNING; |
| ret = 0; |
| out: |
| return ret; |
| } |
| |
| static long userfaultfd_ioctl(struct file *file, unsigned cmd, |
| unsigned long arg) |
| { |
| int ret = -EINVAL; |
| struct userfaultfd_ctx *ctx = file->private_data; |
| |
| switch(cmd) { |
| case UFFDIO_API: |
| ret = userfaultfd_api(ctx, arg); |
| break; |
| case UFFDIO_REGISTER: |
| ret = userfaultfd_register(ctx, arg); |
| break; |
| case UFFDIO_UNREGISTER: |
| ret = userfaultfd_unregister(ctx, arg); |
| break; |
| case UFFDIO_WAKE: |
| ret = userfaultfd_wake(ctx, arg); |
| break; |
| } |
| return ret; |
| } |
| |
| #ifdef CONFIG_PROC_FS |
| static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) |
| { |
| struct userfaultfd_ctx *ctx = f->private_data; |
| wait_queue_t *wq; |
| struct userfaultfd_wait_queue *uwq; |
| unsigned long pending = 0, total = 0; |
| |
| spin_lock(&ctx->fault_pending_wqh.lock); |
| list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) { |
| uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| pending++; |
| total++; |
| } |
| list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { |
| uwq = container_of(wq, struct userfaultfd_wait_queue, wq); |
| total++; |
| } |
| spin_unlock(&ctx->fault_pending_wqh.lock); |
| |
| /* |
| * If more protocols will be added, there will be all shown |
| * separated by a space. Like this: |
| * protocols: aa:... bb:... |
| */ |
| seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", |
| pending, total, UFFD_API, UFFD_API_FEATURES, |
| UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS); |
| } |
| #endif |
| |
| static const struct file_operations userfaultfd_fops = { |
| #ifdef CONFIG_PROC_FS |
| .show_fdinfo = userfaultfd_show_fdinfo, |
| #endif |
| .release = userfaultfd_release, |
| .poll = userfaultfd_poll, |
| .read = userfaultfd_read, |
| .unlocked_ioctl = userfaultfd_ioctl, |
| .compat_ioctl = userfaultfd_ioctl, |
| .llseek = noop_llseek, |
| }; |
| |
| /** |
| * userfaultfd_file_create - Creates an userfaultfd file pointer. |
| * @flags: Flags for the userfaultfd file. |
| * |
| * This function creates an userfaultfd file pointer, w/out installing |
| * it into the fd table. This is useful when the userfaultfd file is |
| * used during the initialization of data structures that require |
| * extra setup after the userfaultfd creation. So the userfaultfd |
| * creation is split into the file pointer creation phase, and the |
| * file descriptor installation phase. In this way races with |
| * userspace closing the newly installed file descriptor can be |
| * avoided. Returns an userfaultfd file pointer, or a proper error |
| * pointer. |
| */ |
| static struct file *userfaultfd_file_create(int flags) |
| { |
| struct file *file; |
| struct userfaultfd_ctx *ctx; |
| |
| BUG_ON(!current->mm); |
| |
| /* Check the UFFD_* constants for consistency. */ |
| BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC); |
| BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK); |
| |
| file = ERR_PTR(-EINVAL); |
| if (flags & ~UFFD_SHARED_FCNTL_FLAGS) |
| goto out; |
| |
| file = ERR_PTR(-ENOMEM); |
| ctx = kmalloc(sizeof(*ctx), GFP_KERNEL); |
| if (!ctx) |
| goto out; |
| |
| atomic_set(&ctx->refcount, 1); |
| init_waitqueue_head(&ctx->fault_pending_wqh); |
| init_waitqueue_head(&ctx->fault_wqh); |
| init_waitqueue_head(&ctx->fd_wqh); |
| ctx->flags = flags; |
| ctx->state = UFFD_STATE_WAIT_API; |
| ctx->released = false; |
| ctx->mm = current->mm; |
| /* prevent the mm struct to be freed */ |
| atomic_inc(&ctx->mm->mm_users); |
| |
| file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx, |
| O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS)); |
| if (IS_ERR(file)) |
| kfree(ctx); |
| out: |
| return file; |
| } |
| |
| SYSCALL_DEFINE1(userfaultfd, int, flags) |
| { |
| int fd, error; |
| struct file *file; |
| |
| error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS); |
| if (error < 0) |
| return error; |
| fd = error; |
| |
| file = userfaultfd_file_create(flags); |
| if (IS_ERR(file)) { |
| error = PTR_ERR(file); |
| goto err_put_unused_fd; |
| } |
| fd_install(fd, file); |
| |
| return fd; |
| |
| err_put_unused_fd: |
| put_unused_fd(fd); |
| |
| return error; |
| } |