The patch titled Subject: mm/uffd: fix pte marker when fork() without fork event has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-uffd-fix-pte-marker-when-fork-without-fork-event.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Peter Xu peterx@redhat.com Subject: mm/uffd: fix pte marker when fork() without fork event Date: Wed, 14 Dec 2022 15:04:52 -0500

Patch series "mm: Fixes on pte markers".

Patch 1 resolves the syzkiller report from Pengfei.

Patch 2 further harden pte markers when used with the recent swapin error markers. The major case is we should persist a swapin error marker after fork(), so child shouldn't read a corrupted page.

This patch (of 2):

When fork(), dst_vma is not guaranteed to have VM_UFFD_WP even if src may have it and has pte marker installed. The warning is improper along with the comment. The right thing is to inherit the pte marker when needed, or keep the dst pte empty.

A vague guess is this happened by an accident when there's the prior patch to introduce src/dst vma into this helper during the uffd-wp feature got developed and I probably messed up in the rebase, since if we replace dst_vma with src_vma the warning & comment it all makes sense too.

Hugetlb did exactly the right here (copy_hugetlb_page_range()). Fix the general path.

Reproducer:

https://github.com/xupengfe/syzkaller_logs/blob/main/221208_115556_copy_page...

Bugzilla report: https://bugzilla.kernel.org/show_bug.cgi?id=216808

Link: https://lkml.kernel.org/r/20221214200453.1772655-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20221214200453.1772655-2-peterx@redhat.com Fixes: c56d1b62cce8 ("mm/shmem: handle uffd-wp during fork()") Signed-off-by: Peter Xu peterx@redhat.com Reported-by: Pengfei Xu pengfei.xu@intel.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: David Hildenbrand david@redhat.com Cc: "Huang, Ying" ying.huang@intel.com Cc: Miaohe Lin linmiaohe@huawei.com Cc: Nadav Amit nadav.amit@gmail.com Cc: stable@vger.kernel.org # 5.19+ Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)

--- a/mm/memory.c~mm-uffd-fix-pte-marker-when-fork-without-fork-event +++ a/mm/memory.c @@ -828,12 +828,8 @@ copy_nonpresent_pte(struct mm_struct *ds return -EBUSY; return -ENOENT; } else if (is_pte_marker_entry(entry)) { - /* - * We're copying the pgtable should only because dst_vma has - * uffd-wp enabled, do sanity check. - */ - WARN_ON_ONCE(!userfaultfd_wp(dst_vma)); - set_pte_at(dst_mm, addr, dst_pte, pte); + if (userfaultfd_wp(dst_vma)) + set_pte_at(dst_mm, addr, dst_pte, pte); return 0; } if (!userfaultfd_wp(dst_vma)) _

Patches currently in -mm which might be from peterx@redhat.com are

mm-uffd-fix-pte-marker-when-fork-without-fork-event.patch mm-fix-a-few-rare-cases-of-using-swapin-error-pte-marker.patch