[Cryptography] Speculation re Intel HW cockup; reqs. OS rewrites & slow execution

Bill Frantz frantz at pwpconsult.com
Fri Jan 5 17:47:41 EST 2018


On 1/4/18 at 8:38 PM, frantz at pwpconsult.com (Bill Frantz) wrote:

>On 1/4/18 at 5:06 PM, nico at cryptonector.com (Nico Williams) wrote:
>
>>Speculative execution is necessarily side-effect-having by its potential
>>cache thrashing impact and ability to be impacted by cache thrashing.
>>This necessarily creates side-channels.  It seems unavoidable except by
>>having sandboxed caches, but that's probably not an option for many
>>reasons (including power consumption).
>
>I can imagine speculative execution which does not proceed if 
>the needed data is not already in the cache. If the caching is 
>working as advertised, this will have a small effect on overall 
>performance. (MOst of the data needed is already in the cache.) 
>It will defeat the attacks which use cache presence or absence 
>as a signaling path.

I am informed by an expert in computer speculation that much of 
the performance gain from speculation comes from pre-loading the 
cache with data that will be needed soon, so this idea just 
won't fly.

Cheers - Bill

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