On 10/19/26 03:03, Ning, Hongyu wrote:
> Commit 3c58f641e813 ("userfaultfd: prevent registration of special
> VMAs") prevents userfaultfd registration on shadow stack VMAs to avoid
> bypassing shadow stack protections through UFFDIO_COPY.
>
> The existing shadow stack selftest still expects UFFDIO_REGISTER to
> succeed and uses UFFDIO_COPY to populate the shadow stack. This causes
> the selftest to fail on Kernels containing this security fix.
>
> Update the selftest to verify that UFFDIO_REGISTER rejects shadow stack
> VMAs with EINVAL. Remove the obsolete userfaultfd fault handling thread
> and UFFDIO_COPY test path.
>
> Tested on: Intel shadow stack capable x86_64 platform
>
> Before fix:
> [FAIL] Userfaultfd test with return code 1
>
> After fix:
> [OK] Userfaultfd rejects shadow stack registration (EINVAL)
Interesting, so we wouldn't be able to snapshot+restore an app that uses shadow
stacks.
@Mike: I assume that's not a concern for CRIU etc, right?
>
> Fixes: 3c58f641e813 ("userfaultfd: prevent registration of special VMAs")
>
> Signed-off-by: Hongyu Ning <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
--
Cheers,
David
