[MODERATED] Re: GPZv4

[Borislav Petkov <bp@suse.de>]

On Tue, Apr 17, 2018 at 03:56:55PM -0400, speck for Jon Masters wrote:
> Let's make sure we're talking about the right thing when we talk about
> things being on or off. I usually always talk about a performance
> feature being on or off, not a mitigation. Therefore, I read the above
> as "MD is off by default", meaning the performance feature is disabled.

I mean the opposite. MD is enabled, as it is the default setting
normally, on any CPU that has MD. So the performance feature remains
enabled.

> This is our current thinking. However, AMD disagree with this and prefer
> to leave the feature enabled by default.

Yes.

> That would mean having to (at a minimum) address all of the userspace
> exposure with prctl(), seccomp(), or other interfaces, and get that
> all done within the next month. For the actual browsers, sure, there
> will be process isolation updates.

Yes. Paranoid people can boot with mdd=on - meaning "memory
disambiguation disable - on"

   [ and yap, if anything, we very very quickly need to agree on one
     terminology and stick with it because the confusion will be insane...
   ]

or, in your suggested nomenclature, ssb=off.

The finer-grained stuff we can do in parallel.

> So can you clarify what you meant by "off on AMD" by default?

AFAIK, AMD wants MD on by default, i.e., unchanged from the current
setting. The user who wants to buy into the perf hit and is paranoid
will be able to disable MD and thus enable the mitigation.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--