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
