From acbefe4fc6dab1670ee97e8cb4e378397ecab45e Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Wed, 14 Dec 2022 15:04:52 -0500 Subject: [PATCH] mm/uffd: fix pte marker when fork() without fork event commit 49d6d7fb631345b0f2957a7c4be24ad63903150f upstream. 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@redhat.com Link: https://lkml.kernel.org/r/20221214200453.1772655-2-peterx@redhat.com Fixes: c3f31c7e7913 ("mm/shmem: handle uffd-wp during fork()") Signed-off-by: Peter Xu Reported-by: Pengfei Xu Acked-by: David Hildenbrand Reviewed-by: Miaohe Lin Cc: Andrea Arcangeli Cc: "Huang, Ying" Cc: Nadav Amit Cc: # 5.19+ Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/memory.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 8c8420934d603..f6f93e5b6b023 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -875,12 +875,8 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, 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)) -- 2.39.5