/* * fs/userfaultfd.c * * Copyright (C) 2007 Davide Libenzi * 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 #include #include #include #include #include #include #include #include #include #include #include #include #include enum userfaultfd_state { UFFD_STATE_WAIT_API, UFFD_STATE_RUNNING, }; struct userfaultfd_ctx { /* pseudo fd refcounting */ atomic_t refcount; /* waitqueue head for the userfaultfd page faults */ 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 { unsigned long address; wait_queue_t wq; bool pending; 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; /* don't wake the pending ones to avoid reads to block */ if (uwq->pending && !ACCESS_ONCE(uwq->ctx->released)) goto out; /* len == 0 means wake all */ start = range->start; len = range->len; if (len && (start > uwq->address || start + len <= uwq->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 unsigned long userfault_address(unsigned long address, unsigned int flags, unsigned long reason) { BUILD_BUG_ON(PAGE_SHIFT < UFFD_BITS); address &= PAGE_MASK; if (flags & FAULT_FLAG_WRITE) /* * Encode "write" fault information in the LSB of the * address read by userland, without depending on * FAULT_FLAG_WRITE kernel internal value. */ address |= UFFD_BIT_WRITE; if (reason & VM_UFFD_WP) /* * Encode "reason" fault information as bit number 1 * in the address read by userland. If bit number 1 is * clear it means the reason is a VM_FAULT_MISSING * fault. */ address |= UFFD_BIT_WP; return address; } /* * 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; BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); ctx = vma->vm_userfaultfd_ctx.ctx; if (!ctx) return VM_FAULT_SIGBUS; 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))) return VM_FAULT_SIGBUS; /* * 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 return VM_FAULT_SIGBUS; } /* * Handle nowait, not much to do other than tell it to retry * and wait. */ if (flags & FAULT_FLAG_RETRY_NOWAIT) return VM_FAULT_RETRY; /* 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.address = userfault_address(address, flags, reason); uwq.pending = true; uwq.ctx = ctx; spin_lock(&ctx->fault_wqh.lock); /* * After the __add_wait_queue the uwq is visible to userland * through poll/read(). */ __add_wait_queue(&ctx->fault_wqh, &uwq.wq); for (;;) { set_current_state(TASK_KILLABLE); if (!uwq.pending || ACCESS_ONCE(ctx->released) || fatal_signal_pending(current)) break; spin_unlock(&ctx->fault_wqh.lock); wake_up_poll(&ctx->fd_wqh, POLLIN); schedule(); spin_lock(&ctx->fault_wqh.lock); } __remove_wait_queue(&ctx->fault_wqh, &uwq.wq); __set_current_state(TASK_RUNNING); spin_unlock(&ctx->fault_wqh.lock); /* * ctx may go away after this if the userfault pseudo fd is * already released. */ userfaultfd_ctx_put(ctx); return VM_FAULT_RETRY; } 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_wqh.lock); __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, 0, &range); spin_unlock(&ctx->fault_wqh.lock); wake_up_poll(&ctx->fd_wqh, POLLHUP); userfaultfd_ctx_put(ctx); return 0; } /* fault_wqh.lock must be hold by the caller */ static inline unsigned int find_userfault(struct userfaultfd_ctx *ctx, struct userfaultfd_wait_queue **uwq) { wait_queue_t *wq; struct userfaultfd_wait_queue *_uwq; unsigned int ret = 0; VM_BUG_ON(!spin_is_locked(&ctx->fault_wqh.lock)); list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { _uwq = container_of(wq, struct userfaultfd_wait_queue, wq); if (_uwq->pending) { ret = POLLIN; if (!uwq) /* * If there's at least a pending and * we don't care which one it is, * break immediately and leverage the * efficiency of the LIFO walk. */ break; /* * If we need to find which one was pending we * keep walking until we find the first not * pending one, so we read() them in FIFO order. */ *uwq = _uwq; } else /* * break the loop at the first not pending * one, there cannot be pending userfaults * after the first not pending one, because * all new pending ones are inserted at the * head and we walk it in LIFO. */ break; } return ret; } 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: spin_lock(&ctx->fault_wqh.lock); ret = find_userfault(ctx, NULL); spin_unlock(&ctx->fault_wqh.lock); return ret; default: BUG(); } } static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, __u64 *addr) { ssize_t ret; DECLARE_WAITQUEUE(wait, current); struct userfaultfd_wait_queue *uwq = NULL; /* always take the fd_wqh lock before the fault_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_wqh.lock); if (find_userfault(ctx, &uwq)) { /* * The fault_wqh.lock prevents the uwq to * disappear from under us. */ uwq->pending = false; /* careful to always initialize addr if ret == 0 */ *addr = uwq->address; spin_unlock(&ctx->fault_wqh.lock); ret = 0; break; } spin_unlock(&ctx->fault_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; /* careful to always initialize addr if ret == 0 */ __u64 uninitialized_var(addr); 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(addr)) return ret ? ret : -EINVAL; _ret = userfaultfd_ctx_read(ctx, no_wait, &addr); if (_ret < 0) return ret ? ret : _ret; if (put_user(addr, (__u64 __user *) buf)) return ret ? ret : -EFAULT; ret += sizeof(addr); buf += sizeof(addr); count -= sizeof(addr); /* * 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_wqh.lock); /* wake all in the range and autoremove */ __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, 0, range); spin_unlock(&ctx->fault_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_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; } /* * This is mostly needed to re-wakeup those userfaults that were still * pending when userland wake them up the first time. We don't wake * the pending one to avoid blocking reads to block, or non blocking * read to return -EAGAIN, if used with POLLIN, to avoid userland * doubts on why POLLIN wasn't reliable. */ 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(__u64))) goto out; if (uffdio_api.api != UFFD_API) { /* careful not to leak info, we only read the first 8 bytes */ memset(&uffdio_api, 0, sizeof(uffdio_api)); if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) goto out; ret = -EINVAL; goto out; } /* careful not to leak info, we only read the first 8 bytes */ 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_wqh.lock); list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { uwq = container_of(wq, struct userfaultfd_wait_queue, wq); if (uwq->pending) pending++; total++; } spin_unlock(&ctx->fault_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_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; }