After ptep_clear_flush(), if we find that src_folio is pinned we will fail
UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
src_folio->{mapping,index} is not restored in this process. This is not
what we expected, so fix it.
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Qi Zheng <[email protected]>
---
mm/userfaultfd.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 4744d6a96f96..503ea77c81aa 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1008,9 +1008,6 @@ static int move_present_pte(struct mm_struct *mm,
goto out;
}
- folio_move_anon_rmap(src_folio, dst_vma);
- WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
-
orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
/* Folio got pinned from under us. Put it back and fail the move. */
if (folio_maybe_dma_pinned(src_folio)) {
@@ -1019,6 +1016,9 @@ static int move_present_pte(struct mm_struct *mm,
goto out;
}
+ folio_move_anon_rmap(src_folio, dst_vma);
+ WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+
orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
/* Follow mremap() behavior and treat the entry dirty after the move */
orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);
--
2.30.2
On 22.02.24 09:08, Qi Zheng wrote:
> After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> src_folio->{mapping,index} is not restored in this process. This is not
> what we expected, so fix it.
>
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> Signed-off-by: Qi Zheng <[email protected]>
> ---
> mm/userfaultfd.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 4744d6a96f96..503ea77c81aa 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -1008,9 +1008,6 @@ static int move_present_pte(struct mm_struct *mm,
> goto out;
> }
>
> - folio_move_anon_rmap(src_folio, dst_vma);
> - WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
> -
> orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
> /* Folio got pinned from under us. Put it back and fail the move. */
> if (folio_maybe_dma_pinned(src_folio)) {
> @@ -1019,6 +1016,9 @@ static int move_present_pte(struct mm_struct *mm,
> goto out;
> }
>
> + folio_move_anon_rmap(src_folio, dst_vma);
> + WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
> +
> orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
> /* Follow mremap() behavior and treat the entry dirty after the move */
> orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);
Indeed, LGTM.
Reviewed-by: David Hildenbrand <[email protected]>
--
Cheers,
David / dhildenb
On Thu, 22 Feb 2024 16:08:15 +0800 Qi Zheng <[email protected]> wrote:
> After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> src_folio->{mapping,index} is not restored in this process. This is not
> what we expected, so fix it.
>
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
What are the expected worst-case userspace-visible runtime effects of
this flaw?
On Thu, Feb 22, 2024 at 12:43 AM David Hildenbrand <[email protected]> wrote:
>
> On 22.02.24 09:08, Qi Zheng wrote:
> > After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> > UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> > src_folio->{mapping,index} is not restored in this process. This is not
> > what we expected, so fix it.
> >
> > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> > Signed-off-by: Qi Zheng <[email protected]>
> > ---
> > mm/userfaultfd.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> > index 4744d6a96f96..503ea77c81aa 100644
> > --- a/mm/userfaultfd.c
> > +++ b/mm/userfaultfd.c
> > @@ -1008,9 +1008,6 @@ static int move_present_pte(struct mm_struct *mm,
> > goto out;
> > }
> >
> > - folio_move_anon_rmap(src_folio, dst_vma);
> > - WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
> > -
> > orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
> > /* Folio got pinned from under us. Put it back and fail the move. */
> > if (folio_maybe_dma_pinned(src_folio)) {
> > @@ -1019,6 +1016,9 @@ static int move_present_pte(struct mm_struct *mm,
> > goto out;
> > }
> >
> > + folio_move_anon_rmap(src_folio, dst_vma);
> > + WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
> > +
> > orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
> > /* Follow mremap() behavior and treat the entry dirty after the move */
> > orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);
>
> Indeed, LGTM.
>
> Reviewed-by: David Hildenbrand <[email protected]>
Thanks for catching this! Makes total sense to check before modification.
Reviewed-by: Suren Baghdasaryan <[email protected]>
>
> --
> Cheers,
>
> David / dhildenb
>
On Thu, Feb 22, 2024 at 1:00 PM Andrew Morton <[email protected]> wrote:
>
> On Thu, 22 Feb 2024 16:08:15 +0800 Qi Zheng <[email protected]> wrote:
>
> > After ptep_clear_flush(), if we find that src_folio is pinned we will fail
> > UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
> > src_folio->{mapping,index} is not restored in this process. This is not
> > what we expected, so fix it.
> >
> > Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
>
> What are the expected worst-case userspace-visible runtime effects of
> this flaw?
It can cause rmap for that page to be invalid. I guess memory
corruption might be the visible effect?
On 22.02.24 22:56, Suren Baghdasaryan wrote:
> On Thu, Feb 22, 2024 at 1:00 PM Andrew Morton <[email protected]> wrote:
>>
>> On Thu, 22 Feb 2024 16:08:15 +0800 Qi Zheng <[email protected]> wrote:
>>
>>> After ptep_clear_flush(), if we find that src_folio is pinned we will fail
>>> UFFDIO_MOVE and put src_folio back to src_pte entry, but the change to
>>> src_folio->{mapping,index} is not restored in this process. This is not
>>> what we expected, so fix it.
>>>
>>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
>>
>> What are the expected worst-case userspace-visible runtime effects of
>> this flaw?
>
> It can cause rmap for that page to be invalid. I guess memory
> corruption might be the visible effect?
At least swapout+migration would no longer work, because we might fail
to locate the mappings of that folio.
Memory corruption, not sure.
--
Cheers,
David / dhildenb