Reviewed-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Thanks for the fix, Peter! On Mon, Apr 8, 2024 at 11:59 AM David Hildenbrand <david@xxxxxxxxxx> wrote: > > On 06.04.24 01:19, peterx@xxxxxxxxxx wrote: > > From: Peter Xu <peterx@xxxxxxxxxx> > > > > After UFFDIO_POISON, there can be two kinds of hugetlb pte markers, either > > the POISON one or UFFD_WP one. > > > > Allow change protection to run on a poisoned marker just like !hugetlb > > cases, ignoring the marker irrelevant of the permission. > > > > Here the two bits are mutual exclusive. For example, when install a > > poisoned entry it must not be UFFD_WP already (by checking pte_none() > > before such install). And it also means if UFFD_WP is set there must have > > no POISON bit set. It makes sense because UFFD_WP is a bit to reflect > > permission, and permissions do not apply if the pte is poisoned and > > destined to sigbus. > > > > So here we simply check uffd_wp bit set first, do nothing otherwise. > > > > Attach the Fixes to UFFDIO_POISON work, as before that it should not be > > possible to have poison entry for hugetlb (e.g., hugetlb doesn't do swap, > > so no chance of swapin errors). > > > > Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> > > Cc: David Hildenbrand <david@xxxxxxxxxx> > > Cc: linux-stable <stable@xxxxxxxxxxxxxxx> # 6.6+ > > Link: https://lore.kernel.org/r/000000000000920d5e0615602dd1@xxxxxxxxxx > > Reported-by: syzbot+b07c8ac8eee3d4d8440f@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: fc71884a5f59 ("mm: userfaultfd: add new UFFDIO_POISON ioctl") > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > --- > > mm/hugetlb.c | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 8267e221ca5d..ba7162441adf 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -6960,9 +6960,13 @@ long hugetlb_change_protection(struct vm_area_struct *vma, > > if (!pte_same(pte, newpte)) > > set_huge_pte_at(mm, address, ptep, newpte, psize); > > } else if (unlikely(is_pte_marker(pte))) { > > - /* No other markers apply for now. */ > > - WARN_ON_ONCE(!pte_marker_uffd_wp(pte)); > > - if (uffd_wp_resolve) > > + /* > > + * Do nothing on a poison marker; page is > > + * corrupted, permissons do not apply. Here > > + * pte_marker_uffd_wp()==true implies !poison > > + * because they're mutual exclusive. > > + */ > > + if (pte_marker_uffd_wp(pte) && uffd_wp_resolve) > > /* Safe to modify directly (non-present->none). */ > > huge_pte_clear(mm, address, ptep, psize); > > } else if (!huge_pte_none(pte)) { > > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > > -- > Cheers, > > David / dhildenb >
