Re: [PATCH v2] userfaultfd: prevent registration of special VMAs

["David Hildenbrand (Arm)" <david@kernel.org>]

On 6/18/26 11:50, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
> 
> Vova Tokarev says:
> 
>   userfaultfd allows registration on shadow stack VMAs.  With userfaultfd
>   access, you can register on the shadow stack, discard a page ... and
>   inject a page with chosen return addresses via UFFDIO_COPY.
> 
> Update vma_can_userfault() to reject VM_SHADOW_STACK.
> 
> While on it, also reject VM_SPECIAL so that if a driver would implement
> vm_uffd_ops, it wouldn't be possible to register special VMAs with
> userfaultfd.
> 
> Since VM_SPECIAL includes VM_DONTEXPAND which is set but hugetlb,
> exclude hugetlb VMAs from the check for VM_SPECIAL.
> 
> Reported-by: vova tokarev <vladimirelitokarev@gmail.com>
> Fixes: 54007f818206 ("mm: Introduce VM_SHADOW_STACK for shadow stack memory")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---

Thanks Mike

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David