On Thu, Feb 8, 2018 at 12:02 PM, David Laight <david.lai...@aculab.com> wrote:
> From: Arnd Bergmann
>> Sent: 08 February 2018 15:23
> ...
>> The Winchip is what eventually turned into the VIA Nano, which does
>> have speculative execution, but I don't think the earlier C3 and C7 did,
>> they are much closer to the original Winchip design.
> We had terrible trouble getting (IIRC) the C7 to execute functions
> that were called in 16bit mode and returned in 32bit mode and v.v.
> (for boot code bios calls).
> The problems seemed to imply that it was caching return addresses
> and the translation (to uops) of the instructions that followed.
> So it would effectively decode the first few bytes in the wrong mode.
> So there might be scope for one of these attacks.
> OTOH these devices were so slow that I doubt any are used for anything
> serious - and certainly won't get a kernel update even if they are.
> Also worth nothing that the difference between the cpu and memory
> speeds is much lower - so far fewer instructions could be speculatively
> executed while waiting a cache miss.
> Tempting to disable everything.
>         David

You might think this absolutely crazy, but I would be willing to test
such systems if I can get my hands on the needed hardware that I lack.
I am already doing sanity testing on Intel
i486/i586/i586-MMX/i686-PentiumPro systems, I just don't have the
clone cpus (Cyrix, etc).

While few people are using the 32bit kernel, I don't think we want to
kill it completely just yet.

- Matthew

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