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WSL2-Linux-Kernel
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WSL2-Linux-Kernel/fs/userfaultfd.c

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// SPDX-License-Identifier: GPL-2.0-only
/*
* fs/userfaultfd.c
*
* Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
* Copyright (C) 2008-2009 Red Hat, Inc.
* Copyright (C) 2015 Red Hat, Inc.
*
* Some part derived from fs/eventfd.c (anon inode setup) and
* mm/ksm.c (mm hashing).
*/
#include <linux/list.h>
#include <linux/hashtable.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/mm.h>
#include <linux/mmu_notifier.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>
#include <linux/hugetlb.h>
int sysctl_unprivileged_userfaultfd __read_mostly;
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.
*
* Locking order:
* fd_wqh.lock
* fault_pending_wqh.lock
* fault_wqh.lock
* event_wqh.lock
*
* To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
* since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
* also taken in IRQ context.
*/
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;
/* waitqueue head for events */
wait_queue_head_t event_wqh;
/* a refile sequence protected by fault_pending_wqh lock */
seqcount_spinlock_t refile_seq;
/* pseudo fd refcounting */
refcount_t refcount;
/* userfaultfd syscall flags */
unsigned int flags;
/* features requested from the userspace */
unsigned int features;
/* state machine */
enum userfaultfd_state state;
/* released */
bool released;
/* memory mappings are changing because of non-cooperative event */
bool mmap_changing;
/* mm with one ore more vmas attached to this userfaultfd_ctx */
struct mm_struct *mm;
};
struct userfaultfd_fork_ctx {
struct userfaultfd_ctx *orig;
struct userfaultfd_ctx *new;
struct list_head list;
};
struct userfaultfd_unmap_ctx {
struct userfaultfd_ctx *ctx;
unsigned long start;
unsigned long end;
struct list_head list;
};
struct userfaultfd_wait_queue {
struct uffd_msg msg;
wait_queue_entry_t wq;
struct userfaultfd_ctx *ctx;
bool waken;
};
struct userfaultfd_wake_range {
unsigned long start;
unsigned long len;
};
static int userfaultfd_wake_function(wait_queue_entry_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;
WRITE_ONCE(uwq->waken, true);
/*
* The Program-Order guarantees provided by the scheduler
* ensure uwq->waken is visible before the task is woken.
*/
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(), and the
* wq->private is read before calling the extern function
* "wake_up_state" (which in turns calls try_to_wake_up).
*/
list_del_init(&wq->entry);
}
out:
return ret;
}
/**
* userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
* context.
* @ctx: [in] Pointer to the userfaultfd context.
*/
static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
{
refcount_inc(&ctx->refcount);
}
/**
* 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 (refcount_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->event_wqh.lock));
VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
mmdrop(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,
unsigned int features)
{
struct uffd_msg msg;
msg_init(&msg);
msg.event = UFFD_EVENT_PAGEFAULT;
msg.arg.pagefault.address = address;
/*
* These flags indicate why the userfault occurred:
* - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
* - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
* - Neither of these flags being set indicates a MISSING fault.
*
* Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
* fault. Otherwise, it was a read fault.
*/
if (flags & FAULT_FLAG_WRITE)
msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
if (reason & VM_UFFD_WP)
msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
if (reason & VM_UFFD_MINOR)
msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
if (features & UFFD_FEATURE_THREAD_ID)
msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
return msg;
}
#ifdef CONFIG_HUGETLB_PAGE
/*
* Same functionality as userfaultfd_must_wait below with modifications for
* hugepmd ranges.
*/
static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
struct vm_area_struct *vma,
unsigned long address,
unsigned long flags,
unsigned long reason)
{
struct mm_struct *mm = ctx->mm;
pte_t *ptep, pte;
bool ret = true;
mmap_assert_locked(mm);
ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
if (!ptep)
goto out;
ret = false;
pte = huge_ptep_get(ptep);
/*
* Lockless access: we're in a wait_event so it's ok if it
* changes under us.
*/
if (huge_pte_none(pte))
ret = true;
if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
ret = true;
out:
return ret;
}
#else
static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
struct vm_area_struct *vma,
unsigned long address,
unsigned long flags,
unsigned long reason)
{
return false; /* should never get here */
}
#endif /* CONFIG_HUGETLB_PAGE */
/*
* 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;
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd, _pmd;
pte_t *pte;
bool ret = true;
mmap_assert_locked(mm);
pgd = pgd_offset(mm, address);
if (!pgd_present(*pgd))
goto out;
p4d = p4d_offset(pgd, address);
if (!p4d_present(*p4d))
goto out;
pud = pud_offset(p4d, 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_none(_pmd))
goto out;
ret = false;
if (!pmd_present(_pmd))
goto out;
if (pmd_trans_huge(_pmd)) {
if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
ret = true;
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;
if (!pte_write(*pte) && (reason & VM_UFFD_WP))
ret = true;
pte_unmap(pte);
out:
return ret;
}
static inline long userfaultfd_get_blocking_state(unsigned int flags)
{
if (flags & FAULT_FLAG_INTERRUPTIBLE)
return TASK_INTERRUPTIBLE;
if (flags & FAULT_FLAG_KILLABLE)
return TASK_KILLABLE;
return TASK_UNINTERRUPTIBLE;
}
/*
* 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_lock 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_lock must be released before
* returning it.
*/
vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
{
struct mm_struct *mm = vmf->vma->vm_mm;
struct userfaultfd_ctx *ctx;
struct userfaultfd_wait_queue uwq;
vm_fault_t ret = VM_FAULT_SIGBUS;
bool must_wait;
long blocking_state;
/*
* We don't do userfault handling for the final child pid update.
*
* We also don't do userfault handling during
* coredumping. hugetlbfs has the special
* follow_hugetlb_page() to skip missing pages in the
* FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
* the no_page_table() helper in follow_page_mask(), but the
* shmem_vm_ops->fault method is invoked even during
* coredumping without mmap_lock and it ends up here.
*/
if (current->flags & (PF_EXITING|PF_DUMPCORE))
goto out;
/*
* Coredumping runs without mmap_lock so we can only check that
* the mmap_lock is held, if PF_DUMPCORE was not set.
*/
mmap_assert_locked(mm);
ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
if (!ctx)
goto out;
BUG_ON(ctx->mm != mm);
/* Any unrecognized flag is a bug. */
VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
/* 0 or > 1 flags set is a bug; we expect exactly 1. */
VM_BUG_ON(!reason || (reason & (reason - 1)));
if (ctx->features & UFFD_FEATURE_SIGBUS)
goto out;
if ((vmf->flags & FAULT_FLAG_USER) == 0 &&
ctx->flags & UFFD_USER_MODE_ONLY) {
printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
"sysctl knob to 1 if kernel faults must be handled "
"without obtaining CAP_SYS_PTRACE capability\n");
goto out;
}
/*
* 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_lock.
*/
if (unlikely(READ_ONCE(ctx->released))) {
/*
* Don't return VM_FAULT_SIGBUS in this case, so a non
* cooperative manager can close the uffd after the
* last UFFDIO_COPY, without risking to trigger an
* involuntary SIGBUS if the process was starting the
* userfaultfd while the userfaultfd was still armed
* (but after the last UFFDIO_COPY). If the uffd
* wasn't already closed when the userfault reached
* this point, that would normally be solved by
* userfaultfd_must_wait returning 'false'.
*
* If we were to return VM_FAULT_SIGBUS here, the non
* cooperative manager would be instead forced to
* always call UFFDIO_UNREGISTER before it can safely
* close the uffd.
*/
ret = VM_FAULT_NOPAGE;
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(!(vmf->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(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
#ifdef CONFIG_DEBUG_VM
if (printk_ratelimit()) {
printk(KERN_WARNING
"FAULT_FLAG_ALLOW_RETRY missing %x\n",
vmf->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 (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
goto out;
/* take the reference before dropping the mmap_lock */
userfaultfd_ctx_get(ctx);
init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
uwq.wq.private = current;
uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
ctx->features);
uwq.ctx = ctx;
uwq.waken = false;
blocking_state = userfaultfd_get_blocking_state(vmf->flags);
spin_lock_irq(&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(blocking_state);
spin_unlock_irq(&ctx->fault_pending_wqh.lock);
if (!is_vm_hugetlb_page(vmf->vma))
must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
reason);
else
must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
vmf->address,
vmf->flags, reason);
mmap_read_unlock(mm);
if (likely(must_wait && !READ_ONCE(ctx->released))) {
wake_up_poll(&ctx->fd_wqh, EPOLLIN);
schedule();
}
__set_current_state(TASK_RUNNING);
/*
* Here we race with the list_del; list_add in
* userfaultfd_ctx_read(), however because we don't ever run
* list_del_init() to refile across the two lists, the prev
* and next pointers will never point to self. list_add also
* would never let any of the two pointers to point to
* self. So list_empty_careful won't risk to see both pointers
* pointing to self at any time during the list refile. The
* only case where list_del_init() is called is the full
* removal in the wake function and there we don't re-list_add
* and it's fine not to block on the spinlock. The uwq on this
* kernel stack can be released after the list_del_init.
*/
if (!list_empty_careful(&uwq.wq.entry)) {
spin_lock_irq(&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.entry);
spin_unlock_irq(&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 void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
struct userfaultfd_wait_queue *ewq)
{
struct userfaultfd_ctx *release_new_ctx;
if (WARN_ON_ONCE(current->flags & PF_EXITING))
goto out;
ewq->ctx = ctx;
init_waitqueue_entry(&ewq->wq, current);
release_new_ctx = NULL;
spin_lock_irq(&ctx->event_wqh.lock);
/*
* After the __add_wait_queue the uwq is visible to userland
* through poll/read().
*/
__add_wait_queue(&ctx->event_wqh, &ewq->wq);
for (;;) {
set_current_state(TASK_KILLABLE);
if (ewq->msg.event == 0)
break;
if (READ_ONCE(ctx->released) ||
fatal_signal_pending(current)) {
/*
* &ewq->wq may be queued in fork_event, but
* __remove_wait_queue ignores the head
* parameter. It would be a problem if it
* didn't.
*/
__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
if (ewq->msg.event == UFFD_EVENT_FORK) {
struct userfaultfd_ctx *new;
new = (struct userfaultfd_ctx *)
(unsigned long)
ewq->msg.arg.reserved.reserved1;
release_new_ctx = new;
}
break;
}
spin_unlock_irq(&ctx->event_wqh.lock);
wake_up_poll(&ctx->fd_wqh, EPOLLIN);
schedule();
spin_lock_irq(&ctx->event_wqh.lock);
}
__set_current_state(TASK_RUNNING);
spin_unlock_irq(&ctx->event_wqh.lock);
if (release_new_ctx) {
struct vm_area_struct *vma;
struct mm_struct *mm = release_new_ctx->mm;
/* the various vma->vm_userfaultfd_ctx still points to it */
mmap_write_lock(mm);
for (vma = mm->mmap; vma; vma = vma->vm_next)
if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
vma->vm_flags &= ~__VM_UFFD_FLAGS;
}
mmap_write_unlock(mm);
userfaultfd_ctx_put(release_new_ctx);
}
/*
* ctx may go away after this if the userfault pseudo fd is
* already released.
*/
out:
WRITE_ONCE(ctx->mmap_changing, false);
userfaultfd_ctx_put(ctx);
}
static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
struct userfaultfd_wait_queue *ewq)
{
ewq->msg.event = 0;
wake_up_locked(&ctx->event_wqh);
__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
}
int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
{
struct userfaultfd_ctx *ctx = NULL, *octx;
struct userfaultfd_fork_ctx *fctx;
octx = vma->vm_userfaultfd_ctx.ctx;
if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
vma->vm_flags &= ~__VM_UFFD_FLAGS;
return 0;
}
list_for_each_entry(fctx, fcs, list)
if (fctx->orig == octx) {
ctx = fctx->new;
break;
}
if (!ctx) {
fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
if (!fctx)
return -ENOMEM;
ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
if (!ctx) {
kfree(fctx);
return -ENOMEM;
}
refcount_set(&ctx->refcount, 1);
ctx->flags = octx->flags;
ctx->state = UFFD_STATE_RUNNING;
ctx->features = octx->features;
ctx->released = false;
ctx->mmap_changing = false;
ctx->mm = vma->vm_mm;
mmgrab(ctx->mm);
userfaultfd_ctx_get(octx);
WRITE_ONCE(octx->mmap_changing, true);
fctx->orig = octx;
fctx->new = ctx;
list_add_tail(&fctx->list, fcs);
}
vma->vm_userfaultfd_ctx.ctx = ctx;
return 0;
}
static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
{
struct userfaultfd_ctx *ctx = fctx->orig;
struct userfaultfd_wait_queue ewq;
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_FORK;
ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
userfaultfd_event_wait_completion(ctx, &ewq);
}
void dup_userfaultfd_complete(struct list_head *fcs)
{
struct userfaultfd_fork_ctx *fctx, *n;
list_for_each_entry_safe(fctx, n, fcs, list) {
dup_fctx(fctx);
list_del(&fctx->list);
kfree(fctx);
}
}
void mremap_userfaultfd_prep(struct vm_area_struct *vma,
struct vm_userfaultfd_ctx *vm_ctx)
{
struct userfaultfd_ctx *ctx;
ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx)
return;
if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
vm_ctx->ctx = ctx;
userfaultfd_ctx_get(ctx);
WRITE_ONCE(ctx->mmap_changing, true);
} else {
/* Drop uffd context if remap feature not enabled */
vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
vma->vm_flags &= ~__VM_UFFD_FLAGS;
}
}
void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
unsigned long from, unsigned long to,
unsigned long len)
{
struct userfaultfd_ctx *ctx = vm_ctx->ctx;
struct userfaultfd_wait_queue ewq;
if (!ctx)
return;
if (to & ~PAGE_MASK) {
userfaultfd_ctx_put(ctx);
return;
}
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_REMAP;
ewq.msg.arg.remap.from = from;
ewq.msg.arg.remap.to = to;
ewq.msg.arg.remap.len = len;
userfaultfd_event_wait_completion(ctx, &ewq);
}
bool userfaultfd_remove(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
struct mm_struct *mm = vma->vm_mm;
struct userfaultfd_ctx *ctx;
struct userfaultfd_wait_queue ewq;
ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
return true;
userfaultfd_ctx_get(ctx);
WRITE_ONCE(ctx->mmap_changing, true);
mmap_read_unlock(mm);
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_REMOVE;
ewq.msg.arg.remove.start = start;
ewq.msg.arg.remove.end = end;
userfaultfd_event_wait_completion(ctx, &ewq);
return false;
}
static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
unsigned long start, unsigned long end)
{
struct userfaultfd_unmap_ctx *unmap_ctx;
list_for_each_entry(unmap_ctx, unmaps, list)
if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
unmap_ctx->end == end)
return true;
return false;
}
int userfaultfd_unmap_prep(struct vm_area_struct *vma,
unsigned long start, unsigned long end,
struct list_head *unmaps)
{
for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
struct userfaultfd_unmap_ctx *unmap_ctx;
struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
has_unmap_ctx(ctx, unmaps, start, end))
continue;
unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
if (!unmap_ctx)
return -ENOMEM;
userfaultfd_ctx_get(ctx);
WRITE_ONCE(ctx->mmap_changing, true);
unmap_ctx->ctx = ctx;
unmap_ctx->start = start;
unmap_ctx->end = end;
list_add_tail(&unmap_ctx->list, unmaps);
}
return 0;
}
void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
{
struct userfaultfd_unmap_ctx *ctx, *n;
struct userfaultfd_wait_queue ewq;
list_for_each_entry_safe(ctx, n, uf, list) {
msg_init(&ewq.msg);
ewq.msg.event = UFFD_EVENT_UNMAP;
ewq.msg.arg.remove.start = ctx->start;
ewq.msg.arg.remove.end = ctx->end;
userfaultfd_event_wait_completion(ctx->ctx, &ewq);
list_del(&ctx->list);
kfree(ctx);
}
}
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;
WRITE_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_lock. So
* it's critical that released is set to true (above), before
* taking the mmap_lock for writing.
*/
mmap_write_lock(mm);
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_FLAGS));
if (vma->vm_userfaultfd_ctx.ctx != ctx) {
prev = vma;
continue;
}
new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
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;
}
mmap_write_unlock(mm);
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_irq(&ctx->fault_pending_wqh.lock);
__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
__wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
spin_unlock_irq(&ctx->fault_pending_wqh.lock);
/* Flush pending events that may still wait on event_wqh */
wake_up_all(&ctx->event_wqh);
wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
userfaultfd_ctx_put(ctx);
return 0;
}
/* fault_pending_wqh.lock must be hold by the caller */
static inline struct userfaultfd_wait_queue *find_userfault_in(
wait_queue_head_t *wqh)
{
wait_queue_entry_t *wq;
struct userfaultfd_wait_queue *uwq;
lockdep_assert_held(&wqh->lock);
uwq = NULL;
if (!waitqueue_active(wqh))
goto out;
/* walk in reverse to provide FIFO behavior to read userfaults */
wq = list_last_entry(&wqh->head, typeof(*wq), entry);
uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
out:
return uwq;
}
static inline struct userfaultfd_wait_queue *find_userfault(
struct userfaultfd_ctx *ctx)
{
return find_userfault_in(&ctx->fault_pending_wqh);
}
static inline struct userfaultfd_wait_queue *find_userfault_evt(
struct userfaultfd_ctx *ctx)
{
return find_userfault_in(&ctx->event_wqh);
}
static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
{
struct userfaultfd_ctx *ctx = file->private_data;
__poll_t ret;
poll_wait(file, &ctx->fd_wqh, wait);
switch (ctx->state) {
case UFFD_STATE_WAIT_API:
return EPOLLERR;
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 EPOLLERR;
/*
* 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 = EPOLLIN;
else if (waitqueue_active(&ctx->event_wqh))
ret = EPOLLIN;
return ret;
default:
WARN_ON_ONCE(1);
return EPOLLERR;
}
}
static const struct file_operations userfaultfd_fops;
static int resolve_userfault_fork(struct userfaultfd_ctx *new,
struct inode *inode,
struct uffd_msg *msg)
{
int fd;
fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new,
O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
if (fd < 0)
return fd;
msg->arg.reserved.reserved1 = 0;
msg->arg.fork.ufd = fd;
return 0;
}
static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
struct uffd_msg *msg, struct inode *inode)
{
ssize_t ret;
DECLARE_WAITQUEUE(wait, current);
struct userfaultfd_wait_queue *uwq;
/*
* Handling fork event requires sleeping operations, so
* we drop the event_wqh lock, then do these ops, then
* lock it back and wake up the waiter. While the lock is
* dropped the ewq may go away so we keep track of it
* carefully.
*/
LIST_HEAD(fork_event);
struct userfaultfd_ctx *fork_nctx = NULL;
/* always take the fd_wqh lock before the fault_pending_wqh lock */
spin_lock_irq(&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.head 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.entry);
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);
spin_lock(&ctx->event_wqh.lock);
uwq = find_userfault_evt(ctx);
if (uwq) {
*msg = uwq->msg;
if (uwq->msg.event == UFFD_EVENT_FORK) {
fork_nctx = (struct userfaultfd_ctx *)
(unsigned long)
uwq->msg.arg.reserved.reserved1;
list_move(&uwq->wq.entry, &fork_event);
/*
* fork_nctx can be freed as soon as
* we drop the lock, unless we take a
* reference on it.
*/
userfaultfd_ctx_get(fork_nctx);
spin_unlock(&ctx->event_wqh.lock);
ret = 0;
break;
}
userfaultfd_event_complete(ctx, uwq);
spin_unlock(&ctx->event_wqh.lock);
ret = 0;
break;
}
spin_unlock(&ctx->event_wqh.lock);
if (signal_pending(current)) {
ret = -ERESTARTSYS;
break;
}
if (no_wait) {
ret = -EAGAIN;
break;
}
spin_unlock_irq(&ctx->fd_wqh.lock);
schedule();
spin_lock_irq(&ctx->fd_wqh.lock);
}
__remove_wait_queue(&ctx->fd_wqh, &wait);
__set_current_state(TASK_RUNNING);
spin_unlock_irq(&ctx->fd_wqh.lock);
if (!ret && msg->event == UFFD_EVENT_FORK) {
ret = resolve_userfault_fork(fork_nctx, inode, msg);
spin_lock_irq(&ctx->event_wqh.lock);
if (!list_empty(&fork_event)) {
/*
* The fork thread didn't abort, so we can
* drop the temporary refcount.
*/
userfaultfd_ctx_put(fork_nctx);
uwq = list_first_entry(&fork_event,
typeof(*uwq),
wq.entry);
/*
* If fork_event list wasn't empty and in turn
* the event wasn't already released by fork
* (the event is allocated on fork kernel
* stack), put the event back to its place in
* the event_wq. fork_event head will be freed
* as soon as we return so the event cannot
* stay queued there no matter the current
* "ret" value.
*/
list_del(&uwq->wq.entry);
__add_wait_queue(&ctx->event_wqh, &uwq->wq);
/*
* Leave the event in the waitqueue and report
* error to userland if we failed to resolve
* the userfault fork.
*/
if (likely(!ret))
userfaultfd_event_complete(ctx, uwq);
} else {
/*
* Here the fork thread aborted and the
* refcount from the fork thread on fork_nctx
* has already been released. We still hold
* the reference we took before releasing the
* lock above. If resolve_userfault_fork
* failed we've to drop it because the
* fork_nctx has to be freed in such case. If
* it succeeded we'll hold it because the new
* uffd references it.
*/
if (ret)
userfaultfd_ctx_put(fork_nctx);
}
spin_unlock_irq(&ctx->event_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;
struct inode *inode = file_inode(file);
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, inode);
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)
{
spin_lock_irq(&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(&ctx->fault_wqh, TASK_NORMAL, 1, range);
spin_unlock_irq(&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 mmap_read_unlock(mm) 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;
*start = untagged_addr(*start);
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 inline bool vma_can_userfault(struct vm_area_struct *vma,
unsigned long vm_flags)
{
/* FIXME: add WP support to hugetlbfs and shmem */
if (vm_flags & VM_UFFD_WP) {
if (is_vm_hugetlb_page(vma) || vma_is_shmem(vma))
return false;
}
if (vm_flags & VM_UFFD_MINOR) {
if (!(is_vm_hugetlb_page(vma) || vma_is_shmem(vma)))
return false;
}
return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
vma_is_shmem(vma);
}
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;
bool basic_ioctls;
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 & ~UFFD_API_REGISTER_MODES)
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) {
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
goto out;
#endif
vm_flags |= VM_UFFD_WP;
}
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
goto out;
#endif
vm_flags |= VM_UFFD_MINOR;
}
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;
mmap_write_lock(mm);
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;
/*
* If the first vma contains huge pages, make sure start address
* is aligned to huge page size.
*/
if (is_vm_hugetlb_page(vma)) {
unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
if (start & (vma_hpagesize - 1))
goto out_unlock;
}
/*
* Search for not compatible vmas.
*/
found = false;
basic_ioctls = 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_FLAGS));
/* check not compatible vmas */
ret = -EINVAL;
if (!vma_can_userfault(cur, vm_flags))
goto out_unlock;
/*
* UFFDIO_COPY will fill file holes even without
* PROT_WRITE. This check enforces that if this is a
* MAP_SHARED, the process has write permission to the backing
* file. If VM_MAYWRITE is set it also enforces that on a
* MAP_SHARED vma: there is no F_WRITE_SEAL and no further
* F_WRITE_SEAL can be taken until the vma is destroyed.
*/
ret = -EPERM;
if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
goto out_unlock;
/*
* If this vma contains ending address, and huge pages
* check alignment.
*/
if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
end > cur->vm_start) {
unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
ret = -EINVAL;
if (end & (vma_hpagesize - 1))
goto out_unlock;
}
if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
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;
/*
* Note vmas containing huge pages
*/
if (is_vm_hugetlb_page(cur))
basic_ioctls = true;
found = true;
}
BUG_ON(!found);
if (vma->vm_start < start)
prev = vma;
ret = 0;
do {
cond_resched();
BUG_ON(!vma_can_userfault(vma, vm_flags));
BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
vma->vm_userfaultfd_ctx.ctx != ctx);
WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
/*
* 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_UFFD_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;
if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
hugetlb_unshare_all_pmds(vma);
skip:
prev = vma;
start = vma->vm_end;
vma = vma->vm_next;
} while (vma && vma->vm_start < end);
out_unlock:
mmap_write_unlock(mm);
mmput(mm);
if (!ret) {
__u64 ioctls_out;
ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
UFFD_API_RANGE_IOCTLS;
/*
* Declare the WP ioctl only if the WP mode is
* specified and all checks passed with the range
*/
if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
/* CONTINUE ioctl is only supported for MINOR ranges. */
if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
/*
* Now that we scanned all vmas we can already tell
* userland which ioctls methods are guaranteed to
* succeed on this range.
*/
if (put_user(ioctls_out, &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;
mmap_write_lock(mm);
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;
/*
* If the first vma contains huge pages, make sure start address
* is aligned to huge page size.
*/
if (is_vm_hugetlb_page(vma)) {
unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
if (start & (vma_hpagesize - 1))
goto out_unlock;
}
/*
* Search for not compatible 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_FLAGS));
/*
* 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 (!vma_can_userfault(cur, cur->vm_flags))
goto out_unlock;
found = true;
}
BUG_ON(!found);
if (vma->vm_start < start)
prev = vma;
ret = 0;
do {
cond_resched();
BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
/*
* 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;
WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
if (vma->vm_start > start)
start = vma->vm_start;
vma_end = min(end, vma->vm_end);
if (userfaultfd_missing(vma)) {
/*
* Wake any concurrent pending userfault while
* we unregister, so they will not hang
* permanently and it avoids userland to call
* UFFDIO_WAKE explicitly.
*/
struct userfaultfd_wake_range range;
range.start = start;
range.len = vma_end - start;
wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
}
new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
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:
mmap_write_unlock(mm);
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 = -EAGAIN;
if (READ_ONCE(ctx->mmap_changing))
goto out;
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|UFFDIO_COPY_MODE_WP))
goto out;
if (mmget_not_zero(ctx->mm)) {
ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
uffdio_copy.len, &ctx->mmap_changing,
uffdio_copy.mode);
mmput(ctx->mm);
} else {
return -ESRCH;
}
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 = -EAGAIN;
if (READ_ONCE(ctx->mmap_changing))
goto out;
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,
&ctx->mmap_changing);
mmput(ctx->mm);
} else {
return -ESRCH;
}
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;
}
static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
unsigned long arg)
{
int ret;
struct uffdio_writeprotect uffdio_wp;
struct uffdio_writeprotect __user *user_uffdio_wp;
struct userfaultfd_wake_range range;
bool mode_wp, mode_dontwake;
if (READ_ONCE(ctx->mmap_changing))
return -EAGAIN;
user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
if (copy_from_user(&uffdio_wp, user_uffdio_wp,
sizeof(struct uffdio_writeprotect)))
return -EFAULT;
ret = validate_range(ctx->mm, &uffdio_wp.range.start,
uffdio_wp.range.len);
if (ret)
return ret;
if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
UFFDIO_WRITEPROTECT_MODE_WP))
return -EINVAL;
mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
if (mode_wp && mode_dontwake)
return -EINVAL;
ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
uffdio_wp.range.len, mode_wp,
&ctx->mmap_changing);
if (ret)
return ret;
if (!mode_wp && !mode_dontwake) {
range.start = uffdio_wp.range.start;
range.len = uffdio_wp.range.len;
wake_userfault(ctx, &range);
}
return ret;
}
static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
{
__s64 ret;
struct uffdio_continue uffdio_continue;
struct uffdio_continue __user *user_uffdio_continue;
struct userfaultfd_wake_range range;
user_uffdio_continue = (struct uffdio_continue __user *)arg;
ret = -EAGAIN;
if (READ_ONCE(ctx->mmap_changing))
goto out;
ret = -EFAULT;
if (copy_from_user(&uffdio_continue, user_uffdio_continue,
/* don't copy the output fields */
sizeof(uffdio_continue) - (sizeof(__s64))))
goto out;
ret = validate_range(ctx->mm, &uffdio_continue.range.start,
uffdio_continue.range.len);
if (ret)
goto out;
ret = -EINVAL;
/* double check for wraparound just in case. */
if (uffdio_continue.range.start + uffdio_continue.range.len <=
uffdio_continue.range.start) {
goto out;
}
if (uffdio_continue.mode & ~UFFDIO_CONTINUE_MODE_DONTWAKE)
goto out;
if (mmget_not_zero(ctx->mm)) {
ret = mcopy_continue(ctx->mm, uffdio_continue.range.start,
uffdio_continue.range.len,
&ctx->mmap_changing);
mmput(ctx->mm);
} else {
return -ESRCH;
}
if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
return -EFAULT;
if (ret < 0)
goto out;
/* len == 0 would wake all */
BUG_ON(!ret);
range.len = ret;
if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
range.start = uffdio_continue.range.start;
wake_userfault(ctx, &range);
}
ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
out:
return ret;
}
static inline unsigned int uffd_ctx_features(__u64 user_features)
{
/*
* For the current set of features the bits just coincide
*/
return (unsigned int)user_features;
}
/*
* 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;
__u64 features;
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;
features = uffdio_api.features;
ret = -EINVAL;
if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
goto err_out;
ret = -EPERM;
if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
goto err_out;
/* report all available features and ioctls to userland */
uffdio_api.features = UFFD_API_FEATURES;
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
uffdio_api.features &=
~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
#endif
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
#endif
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;
/* only enable the requested features for this uffd context */
ctx->features = uffd_ctx_features(features);
ret = 0;
out:
return ret;
err_out:
memset(&uffdio_api, 0, sizeof(uffdio_api));
if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
ret = -EFAULT;
goto out;
}
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;
case UFFDIO_WRITEPROTECT:
ret = userfaultfd_writeprotect(ctx, arg);
break;
case UFFDIO_CONTINUE:
ret = userfaultfd_continue(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_entry_t *wq;
unsigned long pending = 0, total = 0;
spin_lock_irq(&ctx->fault_pending_wqh.lock);
list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
pending++;
total++;
}
list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
total++;
}
spin_unlock_irq(&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, ctx->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 = compat_ptr_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->event_wqh);
init_waitqueue_head(&ctx->fd_wqh);
seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
}
SYSCALL_DEFINE1(userfaultfd, int, flags)
{
struct userfaultfd_ctx *ctx;
int fd;
if (!sysctl_unprivileged_userfaultfd &&
(flags & UFFD_USER_MODE_ONLY) == 0 &&
!capable(CAP_SYS_PTRACE)) {
printk_once(KERN_WARNING "uffd: Set unprivileged_userfaultfd "
"sysctl knob to 1 if kernel faults must be handled "
"without obtaining CAP_SYS_PTRACE capability\n");
return -EPERM;
}
BUG_ON(!current->mm);
/* Check the UFFD_* constants for consistency. */
BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
return -EINVAL;
ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
if (!ctx)
return -ENOMEM;
refcount_set(&ctx->refcount, 1);
ctx->flags = flags;
ctx->features = 0;
ctx->state = UFFD_STATE_WAIT_API;
ctx->released = false;
ctx->mmap_changing = false;
ctx->mm = current->mm;
/* prevent the mm struct to be freed */
mmgrab(ctx->mm);
fd = anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx,
O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
if (fd < 0) {
mmdrop(ctx->mm);
kmem_cache_free(userfaultfd_ctx_cachep, ctx);
}
return fd;
}
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);
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