Re: [PATCH v5 1/2] Add UFFD_USER_MODE_ONLY

[Andrea Arcangeli]

On Sat, Oct 10, 2020 at 11:24:55PM -0700, Lokesh Gidra wrote:
> userfaultfd handles page faults from both user and kernel code.
> Add a new UFFD_USER_MODE_ONLY flag for userfaultfd(2) that makes
> the resulting userfaultfd object refuse to handle faults from kernel
> mode, treating these faults as if SIGBUS were always raised, causing
> the kernel code to fail with EFAULT.
> 
> A future patch adds a knob allowing administrators to give some
> processes the ability to create userfaultfd file objects only if they
> pass UFFD_USER_MODE_ONLY, reducing the likelihood that these processes
> will exploit userfaultfd's ability to delay kernel page faults to open
> timing windows for future exploits.
> 
> Signed-off-by: Daniel Colascione <dancol@xxxxxxxxxx>
> Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>

Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>