Re: Meltdown / Spectre

[Alex Vong <alexvong1995@gmail.com>]

Tobias Geerinckx-Rice <me@tobias.gr> writes:

> Hej Marius,
>
> [I see this is being CC'd to @libreboot.org. I'm answering only as a GNU
>  Guix user and contributor, and assume people who live and breathe this
>  stuff will find plenty of holes in my opinion. Which this is.]
>
> Marius Bakke wrote on 08/01/18 at 19:26:
>> In my opinion, CPU microcode falls under "non-functional data", as
>> expressly permitted by the GNU FSDG.
>
> I'm not sure how tongue-in-cheek this is, so I'm not sure how to
> respond. I hope nobody on the Internet is wrong^Wseriously suggesting
> that microcode or any other firmware isn't machine code and —
> unfortunately for everyone everywhere — very (dis)functional indeed.
>
> (Don't get me wrong: I wish it weren't so, or that there were some sort
>  of commonly-agreed-upon wink-nudge fiction that it wasn't. If there is,
>  then Debian isn't playing along: microcode blobs are ‘non-free’[0].)
>
> I think the real and thornier question for GuixSD is: if the recent CPU
> vulnerabilities require a microcode update to fully mitigate, then how
> do we square not recommending proprietary globs like this in official
> channels with giving users all knowledge required to decide for themselves?
>
For this particular question, I think we can point users to this
discussion thread in the news section for example. Then they can decide
for themselves what to do. I think this is close to the best thing we
can do now.

>> It is not required for the processor to function, it is merely *a
>> posteriori* data that the CPU can use to fix erratic behaviour.
>
> AIUI, at least on x86 CPUs, the microcode *is* a large and/or functional
> part of the processor. I suspect that's the case for most sufficiently
> modern (complex) chips, but it's not my field.
>
Agree, in my assembly programming course, the lecturer mentioned that
(if I recall correctly) a mircrocode update can bring new instruction
set to a CPU, so it is a very programmable part of the CPU.

> Kind regards,
>
> T G-R
>
> [0]: https://lists.debian.org/debian-devel/2012/11/msg00109.html,
>      https://packages.debian.org/search?keywords=microcode