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![Oleg Nesterov](/assets/img/avatar_default.png)
userfaultfd_file_create() increments mm->mm_users; this means that the memory won't be unmapped/freed if mm owner exits/execs, and UFFDIO_COPY after that can populate the orphaned mm more. Change userfaultfd_file_create() and userfaultfd_ctx_put() to use mm->mm_count to pin mm_struct. This means that atomic_inc_not_zero(mm->mm_users) is needed when we are going to actually play with this memory. Except handle_userfault() path doesn't need this, the caller must already have a reference. The patch adds the new trivial helper, mmget_not_zero(), it can have more users. Link: http://lkml.kernel.org/r/20160516172254.GA8595@redhat.com Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1353 lines
35 KiB
C
1353 lines
35 KiB
C
/*
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* fs/userfaultfd.c
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*
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* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
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* Copyright (C) 2008-2009 Red Hat, Inc.
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* Copyright (C) 2015 Red Hat, Inc.
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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* Some part derived from fs/eventfd.c (anon inode setup) and
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* mm/ksm.c (mm hashing).
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*/
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#include <linux/hashtable.h>
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/poll.h>
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#include <linux/slab.h>
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#include <linux/seq_file.h>
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#include <linux/file.h>
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#include <linux/bug.h>
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#include <linux/anon_inodes.h>
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#include <linux/syscalls.h>
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#include <linux/userfaultfd_k.h>
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#include <linux/mempolicy.h>
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#include <linux/ioctl.h>
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#include <linux/security.h>
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static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
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enum userfaultfd_state {
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UFFD_STATE_WAIT_API,
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UFFD_STATE_RUNNING,
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};
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/*
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* Start with fault_pending_wqh and fault_wqh so they're more likely
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* to be in the same cacheline.
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*/
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struct userfaultfd_ctx {
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/* waitqueue head for the pending (i.e. not read) userfaults */
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wait_queue_head_t fault_pending_wqh;
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/* waitqueue head for the userfaults */
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wait_queue_head_t fault_wqh;
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/* waitqueue head for the pseudo fd to wakeup poll/read */
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wait_queue_head_t fd_wqh;
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/* a refile sequence protected by fault_pending_wqh lock */
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struct seqcount refile_seq;
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/* pseudo fd refcounting */
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atomic_t refcount;
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/* userfaultfd syscall flags */
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unsigned int flags;
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/* state machine */
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enum userfaultfd_state state;
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/* released */
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bool released;
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/* mm with one ore more vmas attached to this userfaultfd_ctx */
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struct mm_struct *mm;
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};
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struct userfaultfd_wait_queue {
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struct uffd_msg msg;
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wait_queue_t wq;
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struct userfaultfd_ctx *ctx;
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};
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struct userfaultfd_wake_range {
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unsigned long start;
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unsigned long len;
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};
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static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode,
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int wake_flags, void *key)
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{
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struct userfaultfd_wake_range *range = key;
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int ret;
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struct userfaultfd_wait_queue *uwq;
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unsigned long start, len;
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uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
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ret = 0;
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/* len == 0 means wake all */
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start = range->start;
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len = range->len;
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if (len && (start > uwq->msg.arg.pagefault.address ||
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start + len <= uwq->msg.arg.pagefault.address))
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goto out;
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ret = wake_up_state(wq->private, mode);
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if (ret)
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/*
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* Wake only once, autoremove behavior.
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*
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* After the effect of list_del_init is visible to the
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* other CPUs, the waitqueue may disappear from under
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* us, see the !list_empty_careful() in
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* handle_userfault(). try_to_wake_up() has an
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* implicit smp_mb__before_spinlock, and the
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* wq->private is read before calling the extern
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* function "wake_up_state" (which in turns calls
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* try_to_wake_up). While the spin_lock;spin_unlock;
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* wouldn't be enough, the smp_mb__before_spinlock is
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* enough to avoid an explicit smp_mb() here.
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*/
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list_del_init(&wq->task_list);
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out:
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return ret;
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}
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/**
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* userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
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* context.
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* @ctx: [in] Pointer to the userfaultfd context.
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*
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* Returns: In case of success, returns not zero.
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*/
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static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
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{
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if (!atomic_inc_not_zero(&ctx->refcount))
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BUG();
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}
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/**
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* userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
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* context.
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* @ctx: [in] Pointer to userfaultfd context.
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*
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* The userfaultfd context reference must have been previously acquired either
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* with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
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*/
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static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
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{
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if (atomic_dec_and_test(&ctx->refcount)) {
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VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
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VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
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VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
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VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
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VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
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VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
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mmdrop(ctx->mm);
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kmem_cache_free(userfaultfd_ctx_cachep, ctx);
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}
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}
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static inline void msg_init(struct uffd_msg *msg)
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{
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BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
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/*
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* Must use memset to zero out the paddings or kernel data is
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* leaked to userland.
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*/
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memset(msg, 0, sizeof(struct uffd_msg));
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}
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static inline struct uffd_msg userfault_msg(unsigned long address,
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unsigned int flags,
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unsigned long reason)
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{
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struct uffd_msg msg;
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msg_init(&msg);
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msg.event = UFFD_EVENT_PAGEFAULT;
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msg.arg.pagefault.address = address;
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if (flags & FAULT_FLAG_WRITE)
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/*
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* If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the
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* uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
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* was not set in a UFFD_EVENT_PAGEFAULT, it means it
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* was a read fault, otherwise if set it means it's
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* a write fault.
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*/
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msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
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if (reason & VM_UFFD_WP)
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/*
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* If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
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* uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
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* not set in a UFFD_EVENT_PAGEFAULT, it means it was
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* a missing fault, otherwise if set it means it's a
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* write protect fault.
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*/
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msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
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return msg;
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}
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/*
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* Verify the pagetables are still not ok after having reigstered into
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* the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
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* userfault that has already been resolved, if userfaultfd_read and
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* UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
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* threads.
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*/
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static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
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unsigned long address,
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unsigned long flags,
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unsigned long reason)
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{
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struct mm_struct *mm = ctx->mm;
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd, _pmd;
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pte_t *pte;
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bool ret = true;
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VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
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pgd = pgd_offset(mm, address);
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if (!pgd_present(*pgd))
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goto out;
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pud = pud_offset(pgd, address);
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if (!pud_present(*pud))
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goto out;
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pmd = pmd_offset(pud, address);
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/*
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* READ_ONCE must function as a barrier with narrower scope
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* and it must be equivalent to:
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* _pmd = *pmd; barrier();
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*
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* This is to deal with the instability (as in
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* pmd_trans_unstable) of the pmd.
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*/
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_pmd = READ_ONCE(*pmd);
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if (!pmd_present(_pmd))
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goto out;
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ret = false;
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if (pmd_trans_huge(_pmd))
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goto out;
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/*
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* the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
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* and use the standard pte_offset_map() instead of parsing _pmd.
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*/
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pte = pte_offset_map(pmd, address);
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/*
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* Lockless access: we're in a wait_event so it's ok if it
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* changes under us.
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*/
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if (pte_none(*pte))
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ret = true;
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pte_unmap(pte);
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out:
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return ret;
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}
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/*
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* The locking rules involved in returning VM_FAULT_RETRY depending on
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* FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
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* FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
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* recommendation in __lock_page_or_retry is not an understatement.
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*
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* If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
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* before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
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* not set.
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*
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* If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
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* set, VM_FAULT_RETRY can still be returned if and only if there are
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* fatal_signal_pending()s, and the mmap_sem must be released before
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* returning it.
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*/
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int handle_userfault(struct vm_area_struct *vma, unsigned long address,
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unsigned int flags, unsigned long reason)
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{
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struct mm_struct *mm = vma->vm_mm;
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struct userfaultfd_ctx *ctx;
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struct userfaultfd_wait_queue uwq;
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int ret;
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bool must_wait, return_to_userland;
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BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
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ret = VM_FAULT_SIGBUS;
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ctx = vma->vm_userfaultfd_ctx.ctx;
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if (!ctx)
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goto out;
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BUG_ON(ctx->mm != mm);
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VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
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VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
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/*
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* If it's already released don't get it. This avoids to loop
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* in __get_user_pages if userfaultfd_release waits on the
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* caller of handle_userfault to release the mmap_sem.
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*/
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if (unlikely(ACCESS_ONCE(ctx->released)))
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goto out;
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/*
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* We don't do userfault handling for the final child pid update.
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*/
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if (current->flags & PF_EXITING)
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goto out;
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/*
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* Check that we can return VM_FAULT_RETRY.
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*
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* NOTE: it should become possible to return VM_FAULT_RETRY
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* even if FAULT_FLAG_TRIED is set without leading to gup()
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* -EBUSY failures, if the userfaultfd is to be extended for
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* VM_UFFD_WP tracking and we intend to arm the userfault
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* without first stopping userland access to the memory. For
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* VM_UFFD_MISSING userfaults this is enough for now.
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*/
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if (unlikely(!(flags & FAULT_FLAG_ALLOW_RETRY))) {
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/*
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* Validate the invariant that nowait must allow retry
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* to be sure not to return SIGBUS erroneously on
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* nowait invocations.
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*/
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BUG_ON(flags & FAULT_FLAG_RETRY_NOWAIT);
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#ifdef CONFIG_DEBUG_VM
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if (printk_ratelimit()) {
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printk(KERN_WARNING
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"FAULT_FLAG_ALLOW_RETRY missing %x\n", flags);
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dump_stack();
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}
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#endif
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goto out;
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}
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/*
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* Handle nowait, not much to do other than tell it to retry
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* and wait.
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*/
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ret = VM_FAULT_RETRY;
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if (flags & FAULT_FLAG_RETRY_NOWAIT)
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goto out;
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/* take the reference before dropping the mmap_sem */
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userfaultfd_ctx_get(ctx);
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init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
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uwq.wq.private = current;
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uwq.msg = userfault_msg(address, flags, reason);
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uwq.ctx = ctx;
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return_to_userland = (flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
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(FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
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spin_lock(&ctx->fault_pending_wqh.lock);
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/*
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* After the __add_wait_queue the uwq is visible to userland
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* through poll/read().
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*/
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__add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
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/*
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* The smp_mb() after __set_current_state prevents the reads
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* following the spin_unlock to happen before the list_add in
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* __add_wait_queue.
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*/
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set_current_state(return_to_userland ? TASK_INTERRUPTIBLE :
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TASK_KILLABLE);
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spin_unlock(&ctx->fault_pending_wqh.lock);
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must_wait = userfaultfd_must_wait(ctx, address, flags, reason);
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up_read(&mm->mmap_sem);
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if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
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(return_to_userland ? !signal_pending(current) :
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!fatal_signal_pending(current)))) {
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wake_up_poll(&ctx->fd_wqh, POLLIN);
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schedule();
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ret |= VM_FAULT_MAJOR;
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}
|
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|
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__set_current_state(TASK_RUNNING);
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|
|
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if (return_to_userland) {
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if (signal_pending(current) &&
|
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!fatal_signal_pending(current)) {
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/*
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* If we got a SIGSTOP or SIGCONT and this is
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* a normal userland page fault, just let
|
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* userland return so the signal will be
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* handled and gdb debugging works. The page
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* fault code immediately after we return from
|
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* this function is going to release the
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* mmap_sem and it's not depending on it
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* (unlike gup would if we were not to return
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* VM_FAULT_RETRY).
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*
|
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* If a fatal signal is pending we still take
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* the streamlined VM_FAULT_RETRY failure path
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* and there's no need to retake the mmap_sem
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* in such case.
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*/
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down_read(&mm->mmap_sem);
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ret = 0;
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}
|
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}
|
|
|
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/*
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* Here we race with the list_del; list_add in
|
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* userfaultfd_ctx_read(), however because we don't ever run
|
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* list_del_init() to refile across the two lists, the prev
|
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* 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.
|
|
*/
|
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if (!list_empty_careful(&uwq.wq.task_list)) {
|
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spin_lock(&ctx->fault_pending_wqh.lock);
|
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/*
|
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* No need of list_del_init(), the uwq on the stack
|
|
* will be freed shortly anyway.
|
|
*/
|
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list_del(&uwq.wq.task_list);
|
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spin_unlock(&ctx->fault_pending_wqh.lock);
|
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}
|
|
|
|
/*
|
|
* 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;
|
|
|
|
if (!mmget_not_zero(mm))
|
|
goto wakeup;
|
|
|
|
/*
|
|
* 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);
|
|
mmput(mm);
|
|
wakeup:
|
|
/*
|
|
* 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;
|
|
|
|
ret = -ENOMEM;
|
|
if (!mmget_not_zero(mm))
|
|
goto out;
|
|
|
|
down_write(&mm->mmap_sem);
|
|
vma = find_vma_prev(mm, start, &prev);
|
|
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);
|
|
mmput(mm);
|
|
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;
|
|
|
|
ret = -ENOMEM;
|
|
if (!mmget_not_zero(mm))
|
|
goto out;
|
|
|
|
down_write(&mm->mmap_sem);
|
|
vma = find_vma_prev(mm, start, &prev);
|
|
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);
|
|
mmput(mm);
|
|
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;
|
|
if (mmget_not_zero(ctx->mm)) {
|
|
ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
|
|
uffdio_copy.len);
|
|
mmput(ctx->mm);
|
|
}
|
|
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;
|
|
|
|
if (mmget_not_zero(ctx->mm)) {
|
|
ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
|
|
uffdio_zeropage.range.len);
|
|
mmput(ctx->mm);
|
|
}
|
|
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_count);
|
|
|
|
file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
|
|
O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
|
|
if (IS_ERR(file)) {
|
|
mmdrop(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);
|