Commit 099dd687 authored by Peter Xu's avatar Peter Xu Committed by Linus Torvalds
Browse files

mm/swap: fix pte_same_as_swp() not removing uffd-wp bit when compare 

I found it by pure code review, that pte_same_as_swp() of unuse_vma()
didn't take uffd-wp bit into account when comparing ptes.
pte_same_as_swp() returning false negative could cause failure to
swapoff swap ptes that was wr-protected by userfaultfd.

Link: https://lkml.kernel.org/r/20210603180546.9083-1-peterx@redhat.com


Fixes: f45ec5ff ("userfaultfd: wp: support swap and page migration")
Signed-off-by: default avatarPeter Xu <peterx@redhat.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>	[5.7+]
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 25182f05

include/linux/swapops.h

+11 −4
Original line number Diff line number Diff line
@@ -23,6 +23,16 @@ 
#define SWP_TYPE_SHIFT	(BITS_PER_XA_VALUE - MAX_SWAPFILES_SHIFT)

#define SWP_OFFSET_MASK	((1UL << SWP_TYPE_SHIFT) - 1)



/* Clear all flags but only keep swp_entry_t related information */

static inline pte_t pte_swp_clear_flags(pte_t pte)

{

	if (pte_swp_soft_dirty(pte))

		pte = pte_swp_clear_soft_dirty(pte);

	if (pte_swp_uffd_wp(pte))

		pte = pte_swp_clear_uffd_wp(pte);

	return pte;

}



/*

 * Store a type+offset into a swp_entry_t in an arch-independent format

 */
@@ -66,10 +76,7 @@ static inline swp_entry_t pte_to_swp_entry(pte_t pte) 
{

	swp_entry_t arch_entry;



	if (pte_swp_soft_dirty(pte))

		pte = pte_swp_clear_soft_dirty(pte);

	if (pte_swp_uffd_wp(pte))

		pte = pte_swp_clear_uffd_wp(pte);

	pte = pte_swp_clear_flags(pte);

	arch_entry = __pte_to_swp_entry(pte);

	return swp_entry(__swp_type(arch_entry), __swp_offset(arch_entry));

}

mm/swapfile.c

+1 −1
Original line number Diff line number Diff line
@@ -1900,7 +1900,7 @@ unsigned int count_swap_pages(int type, int free) 


static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)

{

	return pte_same(pte_swp_clear_soft_dirty(pte), swp_pte);

	return pte_same(pte_swp_clear_flags(pte), swp_pte);

}



/*