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

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commit 099dd6878b9b12d6bbfa6bf29ce0c8ddd38f6901 upstream.

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: f45ec5ff16 ("userfaultfd: wp: support swap and page migration")
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>	[5.7+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Xu 2021-06-15 18:23:16 -07:00 committed by Greg Kroah-Hartman
parent fc7fdd8c5c
commit 12eb3c2c1a
2 changed files with 12 additions and 5 deletions
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15
include/linux/swapops.h
View File

@ -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));
}

2
mm/swapfile.c
View File

@ -1903,7 +1903,7 @@ 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);
}
/*