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/mm-uffd-fix-pte-marker-when-fork-without-fork-event.patch
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@xxxxxxxxxx>
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_range/repro.c
Bugzilla report: https://bugzilla.kernel.org/show_bug.cgi?id=216808
Link: https://lkml.kernel.org/r/20221214200453.1772655-1-peterx@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20221214200453.1772655-2-peterx@xxxxxxxxxx
Fixes: c56d1b62cce8 ("mm/shmem: handle uffd-wp during fork()")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reported-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 5.19+
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx 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
