The quilt patch titled Subject: mm/uffd: sanity check write bit for uffd-wp protected ptes has been removed from the -mm tree. Its filename was mm-uffd-sanity-check-write-bit-for-uffd-wp-protected-ptes.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Peter Xu <peterx@xxxxxxxxxx> Subject: mm/uffd: sanity check write bit for uffd-wp protected ptes Date: Sun, 13 Nov 2022 19:04:47 -0500 Let's add one sanity check for CONFIG_DEBUG_VM on the write bit in whatever chance we have when walking through the pgtables. It can bring the error earlier even before the app notices the data was corrupted on the snapshot. Also it helps us to identify this is a wrong pgtable setup, so hopefully a great information to have for debugging too. Link: https://lkml.kernel.org/r/20221114000447.1681003-3-peterx@xxxxxxxxxx Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Alistair Popple <apopple@xxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Nadav Amit <nadav.amit@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/x86/include/asm/pgtable.h | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) --- a/arch/x86/include/asm/pgtable.h~mm-uffd-sanity-check-write-bit-for-uffd-wp-protected-ptes +++ a/arch/x86/include/asm/pgtable.h @@ -292,7 +292,23 @@ static inline pte_t pte_clear_flags(pte_ #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP static inline int pte_uffd_wp(pte_t pte) { - return pte_flags(pte) & _PAGE_UFFD_WP; + bool wp = pte_flags(pte) & _PAGE_UFFD_WP; + +#ifdef CONFIG_DEBUG_VM + /* + * Having write bit for wr-protect-marked present ptes is fatal, + * because it means the uffd-wp bit will be ignored and write will + * just go through. + * + * Use any chance of pgtable walking to verify this (e.g., when + * page swapped out or being migrated for all purposes). It means + * something is already wrong. Tell the admin even before the + * process crashes. We also nail it with wrong pgtable setup. + */ + WARN_ON_ONCE(wp && pte_write(pte)); +#endif + + return wp; } static inline pte_t pte_mkuffd_wp(pte_t pte) _ Patches currently in -mm which might be from peterx@xxxxxxxxxx are mm-migrate-fix-read-only-page-got-writable-when-recover-pte.patch mm-hugetlb-let-vma_offset_start-to-return-start.patch mm-hugetlb-dont-wait-for-migration-entry-during-follow-page.patch mm-hugetlb-document-huge_pte_offset-usage.patch mm-hugetlb-move-swap-entry-handling-into-vma-lock-when-faulted.patch mm-hugetlb-make-userfaultfd_huge_must_wait-safe-to-pmd-unshare.patch mm-hugetlb-make-hugetlb_follow_page_mask-safe-to-pmd-unshare.patch mm-hugetlb-make-follow_hugetlb_page-safe-to-pmd-unshare.patch mm-hugetlb-make-walk_hugetlb_range-safe-to-pmd-unshare.patch mm-hugetlb-make-page_vma_mapped_walk-safe-to-pmd-unshare.patch mm-hugetlb-introduce-hugetlb_walk.patch mm-hugetlb-introduce-hugetlb_walk-fix.patch mm-hugetlb-introduce-hugetlb_walk-fix-2.patch