Re: [PATCH v3 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control

[Peter Xu]

On Mon, Jun 13, 2022 at 02:55:40PM -0700, Andrew Morton wrote:
> On Wed,  1 Jun 2022 14:09:47 -0700 Axel Rasmussen <axelrasmussen@xxxxxxxxxx> wrote:
> 
> > To achieve this, add a /dev/userfaultfd misc device. This device
> > provides an alternative to the userfaultfd(2) syscall for the creation
> > of new userfaultfds. The idea is, any userfaultfds created this way will
> > be able to handle kernel faults, without the caller having any special
> > capabilities. Access to this mechanism is instead restricted using e.g.
> > standard filesystem permissions.
> 
> The use of a /dev node isn't pretty.  Why can't this be done by
> tweaking sys_userfaultfd() or by adding a sys_userfaultfd2()?
> 
> Peter, will you be completing review of this patchset?

Sorry to not have reviewed it proactively..

I think it's because I never had a good picture/understanding of what
should be the best security model for uffd, meanwhile I am (it seems) just
seeing more and more ways to "provide a safer uffd" by different people
using different ways.. and I never had time (and probably capability too..)
to figure out the correct approach if not to accept all options provided.

I think I'll just assume the whole thing is acked already from you
generally, then I'll read at least the implementation before the end of
tomorrow.

Thanks,

-- 
Peter Xu