The patch titled
Subject: userfaultfd: avoid huge_zero_page in UFFDIO_MOVE
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
userfaultfd-avoid-huge_zero_page-in-uffdio_move.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/userfaultfd-avoid-huge_zero_page-in-uffdio_move.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: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Subject: userfaultfd: avoid huge_zero_page in UFFDIO_MOVE
Date: Thu, 11 Jan 2024 17:39:35 -0800
While testing UFFDIO_MOVE ioctl, syzbot triggered VM_BUG_ON_PAGE caused by
a call to PageAnonExclusive() with a huge_zero_page as a parameter.
UFFDIO_MOVE does not yet handle zeropages and returns EBUSY when one is
encountered. Add an early huge_zero_page check in the PMD move path to
avoid this situation.
Link: https://lkml.kernel.org/r/20240112013935.1474648-1-surenb@xxxxxxxxxx
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Reported-by: syzbot+705209281e36404998f6@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/userfaultfd.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/mm/userfaultfd.c~userfaultfd-avoid-huge_zero_page-in-uffdio_move
+++ a/mm/userfaultfd.c
@@ -1393,6 +1393,12 @@ ssize_t move_pages(struct userfaultfd_ct
err = -ENOENT;
break;
}
+ /* Avoid moving zeropages for now */
+ if (is_huge_zero_pmd(*src_pmd)) {
+ spin_unlock(ptl);
+ err = -EBUSY;
+ break;
+ }
/* Check if we can move the pmd without splitting it. */
if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
_
Patches currently in -mm which might be from surenb@xxxxxxxxxx are
userfaultfd-avoid-huge_zero_page-in-uffdio_move.patch
