Re: x86, microcode: BUG: microcode update that changes x86_capability

From: Henrique de Moraes Holschuh
Date: Fri Sep 19 2014 - 12:11:28 EST

On Thu, 18 Sep 2014, Andy Lutomirski wrote:
> > [2] instantly segfaulting every running process using libpthread-2.19,
> > as well as any other users of Intel TSX.
> >
> >
> > And yes, this means we will kill support for microcode updates
> > outside of the initramfs/early-initramfs, at least in Debian,
> > and likely in Ubuntu.
> Given that there is exactly one microcode update like this (at least of
> the sort that blows up userspace), I think that we should seriously
> consider blacklisting just this particular microcode update once
> userspace is running.

This was just the first one. It is likely that there will be others.

Anyway, IMHO kernel blacklists are of limited value for this kind of issue.
Sure, we can add them to the microcode driver (*not* the early microcode
driver) to protect the unwary after the fact, but the useful fast-reaction
blacklisting will be done by the distros in userspace.

In fact, a big thank-you to Canonical's QA process and to Felix Geyer, for
raising the early alarm (

"One disk to rule them all, One disk to find them. One disk to bring
them all and in the darkness grind them. In the Land of Redmond
where the shadows lie." -- The Silicon Valley Tarot
Henrique Holschuh
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