--- /dev/null
+/*
+ * 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);
Code Review / kvmfornfv.git / blobdiff