[MODERATED] Re: [PATCH 0/2] more sampling fun 0

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Feb 20, 2020 at 07:40:07AM -0800, speck for mark gross wrote:
> On Thu, Feb 20, 2020 at 03:27:20PM +0100, speck for Greg KH wrote:
> > On Thu, Feb 20, 2020 at 09:14:20AM +0100, speck for Greg KH wrote:
> > > On Wed, Feb 19, 2020 at 02:45:22PM -0800, speck for mark gross wrote:
> > > > From: mark gross <mgross@linux.intel.com>
> > > > Subject: [PATCH 0/2] Special Register Buffer Data Sampling patch set 
> > > > 
> > > > Special Register Buffer Data Sampling is a sampling type of vulnerability that
> > > > leaks data across cores sharing the HW-RNG for vulnerable processors.
> > > > 
> > > > This leak is fixed by a microcode update and is enabled by default.
> > > > 
> > > > This new microcode serializes processor access during execution of RDRAND
> > > > or RDSEED. It ensures that the shared buffer is overwritten before it
> > > > is released for reuse.
> > > > 
> > > > The mitigation impacts the throughput of the RDRAND and RDSEED instructions
> > > > and latency of RT processing running on the socket while executing RDRAND or
> > > > RDSEED.  The micro bechmark of calling RDRAND many times shows a 10x slowdown.
> > > 
> > > Then we need to stop using RDRAND internally for our "give me a random
> > > number api" which has spread to more and more parts of the kernel.
> > > 
> > > Here's a patch that does so:
> > > 	https://lore.kernel.org/lkml/20200216161836.1976-1-Jason@zx2c4.com/
> > > which I'm going to advise get merged now and backported to the stable
> > > branches.
> > 
> > Note, the author of that patch has reached out to me to say they found
> > this same issue.  He did so independantly so odds are others already
> > know about this.  He found it because he was wondering why rdrand was so
> > slow on newer systems, and then traced things backwards like all the
> > other researchers in this area.
> Are you saying the author has seen the RNG data leaking across processors or
> the slowdown?

slowdown from what?  Relative to older processors, yes.

Leaking across, yes, I think so.

> > So, what's the timeline here?  Looks like this is already "in the wild"
> > from what I can tell.
> >
> The uCode mitigation is coming out with the 2020.1 IPU (intel platform update)
> (fist ucode update of 2020) that I belive is slated for an official May
> disclosure.

{sigh}  That's a long time, we should just fix up the kernel internally
to not worry about this now so that we are not sitting on this any
longer.

thanks,

greg k-h