diff options
Diffstat (limited to 'kernel/fs/userfaultfd.c')
| -rw-r--r-- | kernel/fs/userfaultfd.c | 1338 |
1 files changed, 1338 insertions, 0 deletions
diff --git a/kernel/fs/userfaultfd.c b/kernel/fs/userfaultfd.c new file mode 100644 index 000000000..66cdb4461 --- /dev/null +++ b/kernel/fs/userfaultfd.c @@ -0,0 +1,1338 @@ +/* + * 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> + +static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly; + +enum userfaultfd_state { + UFFD_STATE_WAIT_API, + UFFD_STATE_RUNNING, +}; + +/* + * Start with fault_pending_wqh and fault_wqh so they're more likely + * to be in the same cacheline. + */ +struct userfaultfd_ctx { + /* 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; + /* a refile sequence protected by fault_pending_wqh lock */ + struct seqcount refile_seq; + /* pseudo fd refcounting */ + atomic_t refcount; + /* 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); + kmem_cache_free(userfaultfd_ctx_cachep, 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; +} + +/* + * Verify the pagetables are still not ok after having reigstered into + * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any + * userfault that has already been resolved, if userfaultfd_read and + * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different + * threads. + */ +static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, + unsigned long address, + unsigned long flags, + unsigned long reason) +{ + struct mm_struct *mm = ctx->mm; + pgd_t *pgd; + pud_t *pud; + pmd_t *pmd, _pmd; + pte_t *pte; + bool ret = true; + + VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); + + pgd = pgd_offset(mm, address); + if (!pgd_present(*pgd)) + goto out; + pud = pud_offset(pgd, address); + if (!pud_present(*pud)) + goto out; + pmd = pmd_offset(pud, address); + /* + * READ_ONCE must function as a barrier with narrower scope + * and it must be equivalent to: + * _pmd = *pmd; barrier(); + * + * This is to deal with the instability (as in + * pmd_trans_unstable) of the pmd. + */ + _pmd = READ_ONCE(*pmd); + if (!pmd_present(_pmd)) + goto out; + + ret = false; + if (pmd_trans_huge(_pmd)) + goto out; + + /* + * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it + * and use the standard pte_offset_map() instead of parsing _pmd. + */ + pte = pte_offset_map(pmd, address); + /* + * Lockless access: we're in a wait_event so it's ok if it + * changes under us. + */ + if (pte_none(*pte)) + ret = true; + pte_unmap(pte); + +out: + return ret; +} + +/* + * 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; + bool must_wait, return_to_userland; + + 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; + + /* + * We don't do userfault handling for the final child pid update. + */ + if (current->flags & PF_EXITING) + 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); + + init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); + uwq.wq.private = current; + uwq.msg = userfault_msg(address, flags, reason); + uwq.ctx = ctx; + + return_to_userland = (flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) == + (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE); + + 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(return_to_userland ? TASK_INTERRUPTIBLE : + TASK_KILLABLE); + spin_unlock(&ctx->fault_pending_wqh.lock); + + must_wait = userfaultfd_must_wait(ctx, address, flags, reason); + up_read(&mm->mmap_sem); + + if (likely(must_wait && !ACCESS_ONCE(ctx->released) && + (return_to_userland ? !signal_pending(current) : + !fatal_signal_pending(current)))) { + wake_up_poll(&ctx->fd_wqh, POLLIN); + schedule(); + ret |= VM_FAULT_MAJOR; + } + + __set_current_state(TASK_RUNNING); + + if (return_to_userland) { + if (signal_pending(current) && + !fatal_signal_pending(current)) { + /* + * If we got a SIGSTOP or SIGCONT and this is + * a normal userland page fault, just let + * userland return so the signal will be + * handled and gdb debugging works. The page + * fault code immediately after we return from + * this function is going to release the + * mmap_sem and it's not depending on it + * (unlike gup would if we were not to return + * VM_FAULT_RETRY). + * + * If a fatal signal is pending we still take + * the streamlined VM_FAULT_RETRY failure path + * and there's no need to retake the mmap_sem + * in such case. + */ + down_read(&mm->mmap_sem); + ret = 0; + } + } + + /* + * 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, &range); + __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &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) { + /* + * Use a seqcount to repeat the lockless check + * in wake_userfault() to avoid missing + * wakeups because during the refile both + * waitqueue could become empty if this is the + * only userfault. + */ + write_seqcount_begin(&ctx->refile_seq); + + /* + * 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); + + write_seqcount_end(&ctx->refile_seq); + + /* 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; + + 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, + range); + if (waitqueue_active(&ctx->fault_wqh)) + __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range); + spin_unlock(&ctx->fault_pending_wqh.lock); +} + +static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, + struct userfaultfd_wake_range *range) +{ + unsigned seq; + bool need_wakeup; + + /* + * 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. + */ + do { + seq = read_seqcount_begin(&ctx->refile_seq); + need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) || + waitqueue_active(&ctx->fault_wqh); + cond_resched(); + } while (read_seqcount_retry(&ctx->refile_seq, seq)); + if (need_wakeup) + __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 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; +} + +static int userfaultfd_copy(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + __s64 ret; + struct uffdio_copy uffdio_copy; + struct uffdio_copy __user *user_uffdio_copy; + struct userfaultfd_wake_range range; + + user_uffdio_copy = (struct uffdio_copy __user *) arg; + + ret = -EFAULT; + if (copy_from_user(&uffdio_copy, user_uffdio_copy, + /* don't copy "copy" last field */ + sizeof(uffdio_copy)-sizeof(__s64))) + goto out; + + ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len); + if (ret) + goto out; + /* + * double check for wraparound just in case. copy_from_user() + * will later check uffdio_copy.src + uffdio_copy.len to fit + * in the userland range. + */ + ret = -EINVAL; + if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src) + goto out; + if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE) + goto out; + + ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src, + uffdio_copy.len); + if (unlikely(put_user(ret, &user_uffdio_copy->copy))) + return -EFAULT; + if (ret < 0) + goto out; + BUG_ON(!ret); + /* len == 0 would wake all */ + range.len = ret; + if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { + range.start = uffdio_copy.dst; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_copy.len ? 0 : -EAGAIN; +out: + return ret; +} + +static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + __s64 ret; + struct uffdio_zeropage uffdio_zeropage; + struct uffdio_zeropage __user *user_uffdio_zeropage; + struct userfaultfd_wake_range range; + + user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg; + + ret = -EFAULT; + if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage, + /* don't copy "zeropage" last field */ + sizeof(uffdio_zeropage)-sizeof(__s64))) + goto out; + + ret = validate_range(ctx->mm, uffdio_zeropage.range.start, + uffdio_zeropage.range.len); + if (ret) + goto out; + ret = -EINVAL; + if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE) + goto out; + + ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start, + uffdio_zeropage.range.len); + if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) + return -EFAULT; + if (ret < 0) + goto out; + /* len == 0 would wake all */ + BUG_ON(!ret); + range.len = ret; + if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { + range.start = uffdio_zeropage.range.start; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN; +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; + + if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API) + return -EINVAL; + + 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; + case UFFDIO_COPY: + ret = userfaultfd_copy(ctx, arg); + break; + case UFFDIO_ZEROPAGE: + ret = userfaultfd_zeropage(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, +}; + +static void init_once_userfaultfd_ctx(void *mem) +{ + struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem; + + init_waitqueue_head(&ctx->fault_pending_wqh); + init_waitqueue_head(&ctx->fault_wqh); + init_waitqueue_head(&ctx->fd_wqh); + seqcount_init(&ctx->refile_seq); +} + +/** + * 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 = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); + if (!ctx) + goto out; + + atomic_set(&ctx->refcount, 1); + 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)) { + mmput(ctx->mm); + kmem_cache_free(userfaultfd_ctx_cachep, 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; +} + +static int __init userfaultfd_init(void) +{ + userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", + sizeof(struct userfaultfd_ctx), + 0, + SLAB_HWCACHE_ALIGN|SLAB_PANIC, + init_once_userfaultfd_ctx); + return 0; +} +__initcall(userfaultfd_init); |