linux-kernel - Re: [PATCH 7/8] x86, microcode, intel: forbid some incorrect metadata

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Date:	Fri, 8 Aug 2014 17:21:35 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Henrique de Moraes Holschuh <hmh@....eng.br>
Cc:	linux-kernel@...r.kernel.org, H Peter Anvin <hpa@...or.com>
Subject: Re: [PATCH 7/8] x86, microcode, intel: forbid some incorrect metadata

On Fri, Aug 08, 2014 at 10:50:57AM -0300, Henrique de Moraes Holschuh wrote:
> On Fri, 08 Aug 2014, Borislav Petkov wrote:
> > If someone tries to load a microcode blob which has been split and so
> > on, then we should refuse loading. We want to accept microcode from the
> > vendor and nothing else glued together.
> 
> I don't quite get why we should refuse microcode

Because the blob from the official location passes internal validation, I'd
strongly assume. Everything else doesn't.

> that has been split by userspace when the Intel SDM explicitly states
> that tools can do that if there is a need,

Where?

> In these last two weeks I tried to look around for microcode loader
> implementantions, and now I believe we will *never* see microcode with the
> current version of the extended signatures specification.  The loaders in
> the field are just too broken, Intel might as well come up with a new and
> enhanced design that doesn't have so many sharp edges, since nearly everyone
> will have to patch their loaders anyway.

You can't just assume that just because implementations are faulty there
- they should adhere to the SDM and it is authoritative. If the extended
signatures are really needed at some point, implementations will have to
be fixed.

> I will respin the patch without the %1024 comment.  Note that I never
> *removed* any test, we never tested for %1024 in the first place

And I'm saying we should if we're loading the official blob.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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