On 14.12.22 21:04, Peter Xu wrote:
This patch should harden commit 15520a3f0469 ("mm: use pte markers for swap
errors") on using pte markers for swapin errors on a few corner cases.
1. Propagate swapin errors across fork()s: if there're swapin errors in
the parent mm, after fork()s the child should sigbus too when an error
page is accessed.
2. Fix a rare condition race in pte_marker_clear() where a uffd-wp pte
marker can be quickly switched to a swapin error.
3. Explicitly ignore swapin error pte markers in change_protection().
I mostly don't worry on (2) or (3) at all, but we should still have them.
Case (1) is special because it can potentially cause silent data corrupt on
child when parent has swapin error triggered with swapoff, but since swapin
error is rare itself already it's probably not easy to trigger either.
Currently there is a priority difference between the uffd-wp bit and the
swapin error entry, in which the swapin error always has higher
priority (e.g. we don't need to wr-protect a swapin error pte marker).
If there will be a 3rd bit introduced, we'll probably need to consider a
more involved approach so we may need to start operate on the bits. Let's
leave that for later.
This patch is tested with case (1) explicitly where we'll get corrupted
data before in the child if there's existing swapin error pte markers, and
after patch applied the child can be rightfully killed.
We don't need to copy stable for this one since 15520a3f0469 just landed as
part of v6.2-rc1, only "Fixes" applied.
Fixes: 15520a3f0469 ("mm: use pte markers for swap errors")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
