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

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 <[email protected]>
> > 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.
FWIW even if the opcodes are slowed by 10x there is no human noticable impact
on boot times.  IMO its more a risk to RT applications than anything else.

--mark

> Here's a patch that does so:
> 	https://lore.kernel.org/lkml/[email protected]/
> which I'm going to advise get merged now and backported to the stable
> branches.
> 
> thanks,
> 
> greg k-h