Re: [PATCH 00/18] prevent bounds-check bypass via speculative execution

Peter Zijlstra
2018-01-08T11:55:33Z

On Mon, Jan 08, 2018 at 11:43:42AM +0000, Alan Cox wrote:
> On Mon, 8 Jan 2018 11:08:36 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Fri, Jan 05, 2018 at 10:30:16PM -0800, Dan Williams wrote:
> > > On Fri, Jan 5, 2018 at 6:22 PM, Eric W. Biederman <ebiederm@xmission.com> wrote:
> > > > In at least one place (mpls) you are patching a fast path. Compile out
> > > > or don't load mpls by all means. But it is not acceptable to change the
> > > > fast path without even considering performance.
> > >
> > > Performance matters greatly, but I need help to identify a workload
> > > that is representative for this fast path to see what, if any, impact
> > > is incurred. Even better is a review that says "nope, 'index' is not
> > > subject to arbitrary userspace control at this point, drop the patch."
> >
> > I think we're focussing a little too much on pure userspace. That is, we
> > should be saying under the attackers control. Inbound network packets
> > could equally be under the attackers control.
>
> Inbound network packets don't come with a facility to read back and do
> cache timimg.

But could they not be used in conjunction with a local task to prime the
stuff?