Commit 70ccb92f authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

userfaultfd: non-cooperative: userfaultfd_remove revalidate vma in MADV_DONTNEED

userfaultfd_remove() has to be execute before zapping the pagetables or
UFFDIO_COPY could keep filling pages after zap_page_range returned,
which would result in non zero data after a MADV_DONTNEED.

However userfaultfd_remove() may have to release the mmap_sem.  This was
handled correctly in MADV_REMOVE, but MADV_DONTNEED accessed a
potentially stale vma (the very vma passed to zap_page_range(vma, ...)).

The fix consists in revalidating the vma in case userfaultfd_remove()
had to release the mmap_sem.

This also optimizes away an unnecessary down_read/up_read in the
MADV_REMOVE case if UFFD_EVENT_FORK had to be delivered.

It all remains zero runtime cost in case CONFIG_USERFAULTFD=n as
userfaultfd_remove() will be defined as "true" at build time.


Signed-off-by: default avatarAndrea Arcangeli <>
Acked-by: default avatarMike Rapoport <>
Cc: "Dr. David Alan Gilbert" <>
Cc: Mike Kravetz <>
Cc: Pavel Emelyanov <>
Cc: Hillf Danton <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 7eb76d45
......@@ -695,8 +695,7 @@ void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
userfaultfd_event_wait_completion(ctx, &ewq);
void userfaultfd_remove(struct vm_area_struct *vma,
struct vm_area_struct **prev,
bool userfaultfd_remove(struct vm_area_struct *vma,
unsigned long start, unsigned long end)
struct mm_struct *mm = vma->vm_mm;
......@@ -705,13 +704,11 @@ void userfaultfd_remove(struct vm_area_struct *vma,
ctx = vma->vm_userfaultfd_ctx.ctx;
if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
return true;
*prev = NULL; /* We wait for ACK w/o the mmap semaphore */
ewq.msg.event = UFFD_EVENT_REMOVE;
......@@ -720,7 +717,7 @@ void userfaultfd_remove(struct vm_area_struct *vma,
userfaultfd_event_wait_completion(ctx, &ewq);
return false;
static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
......@@ -61,8 +61,7 @@ extern void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *,
unsigned long from, unsigned long to,
unsigned long len);
extern void userfaultfd_remove(struct vm_area_struct *vma,
struct vm_area_struct **prev,
extern bool userfaultfd_remove(struct vm_area_struct *vma,
unsigned long start,
unsigned long end);
......@@ -118,11 +117,11 @@ static inline void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *ctx,
static inline void userfaultfd_remove(struct vm_area_struct *vma,
struct vm_area_struct **prev,
static inline bool userfaultfd_remove(struct vm_area_struct *vma,
unsigned long start,
unsigned long end)
return true;
static inline int userfaultfd_unmap_prep(struct vm_area_struct *vma,
......@@ -513,7 +513,43 @@ static long madvise_dontneed(struct vm_area_struct *vma,
if (!can_madv_dontneed_vma(vma))
return -EINVAL;
userfaultfd_remove(vma, prev, start, end);
if (!userfaultfd_remove(vma, start, end)) {
*prev = NULL; /* mmap_sem has been dropped, prev is stale */
vma = find_vma(current->mm, start);
if (!vma)
return -ENOMEM;
if (start < vma->vm_start) {
* This "vma" under revalidation is the one
* with the lowest vma->vm_start where start
* is also < vma->vm_end. If start <
* vma->vm_start it means an hole materialized
* in the user address space within the
* virtual range passed to MADV_DONTNEED.
return -ENOMEM;
if (!can_madv_dontneed_vma(vma))
return -EINVAL;
if (end > vma->vm_end) {
* Don't fail if end > vma->vm_end. If the old
* vma was splitted while the mmap_sem was
* released the effect of the concurrent
* operation may not cause MADV_DONTNEED to
* have an undefined result. There may be an
* adjacent next vma that we'll walk
* next. userfaultfd_remove() will generate an
* UFFD_EVENT_REMOVE repetition on the
* end-vma->vm_end range, but the manager can
* handle a repetition fine.
end = vma->vm_end;
VM_WARN_ON(start >= end);
zap_page_range(vma, start, end - start);
return 0;
......@@ -554,8 +590,10 @@ static long madvise_remove(struct vm_area_struct *vma,
* mmap_sem.
userfaultfd_remove(vma, prev, start, end);
if (userfaultfd_remove(vma, start, end)) {
/* mmap_sem was not released by userfaultfd_remove() */
error = vfs_fallocate(f,
offset, end - start);
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