linux-kernel - Re: x86, microcode: BUG: microcode update that changes x86

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Date:	Thu, 18 Sep 2014 14:53:28 -0500
From:	Chuck Ebbert <cebbert.lkml@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>
Subject: Re: x86, microcode: BUG: microcode update that changes
 x86_capability

On Thu, 18 Sep 2014 12:14:59 -0700
Andy Lutomirski <luto@...capital.net> wrote:

> On 09/18/2014 06:52 AM, Henrique de Moraes Holschuh wrote:
> > The new Haswell microcode update[1] removes the "hle" (hardware lock
> > elision) processor capability.  And it is not cosmetic, either: Intel TSX
> > opcodes will cause an illegal opcode trap after the microcode update[2].
> > 
> > This means cpu_info()->x86_capability becomes stale after the microcode
> > update.
> > 
> > We could add logic to compute the new x86_capability after a microcode
> > update run, and OOPS the kernel if something too important (i.e. anything
> > the kernel uses) went away.  Otherwise, refresh cpu_info()->x86_capability.
> > 
> > Is that doable?
> > 
> > 
> > [1] sig 0x000306f2, pf mask 0x6f, 2014-09-03, rev 0x0029, size 28672
> >     sig 0x000306c3, pf mask 0x32, 2014-07-03, rev 0x001c, size 21504
> >     sig 0x00040651, pf mask 0x72, 2014-07-03, rev 0x001c, size 20480
> >     sig 0x00040661, pf mask 0x32, 2014-07-03, rev 0x0012, size 23552
> 
> This is HSD136, right?  Do you have a link to where that ucode comes
> from?  Does it have release notes?
> 

https://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=24290&lang=eng

I can't find any release notes.

Haswell-EP is also affected, it appears:

http://techreport.com/news/26911/errata-prompts-intel-to-disable-tsx-in-haswell-early-broadwell-cpus

> > 
> > [2] instantly segfaulting every running process using libpthread-2.19,
> >     as well as any other users of Intel TSX.
> >     https://bugs.launchpad.net/intel/+bug/1370352
> > 
> >     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.
> 

All future updates for these CPUs will have this problem.
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