Date: Mon, 8 Jan 2018 12:55:02 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alan Cox <alan.cox@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Will Deacon <will.deacon@arm.com>,
        Solomon Peachy <pizza@shaftnet.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Christian Lamparter <chunkeey@googlemail.com>,
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        linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
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Subject: Re: [PATCH 00/18] prevent bounds-check bypass via speculative
 execution
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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?