linux-kernel - Re: [PATCH 7/8] x86, microcode, intel: guard against misaligned microcode data

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Date:	Tue, 11 Nov 2014 11:47:00 +0100
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: guard against misaligned
 microcode data

On Sat, Nov 08, 2014 at 07:57:49PM -0200, Henrique de Moraes Holschuh wrote:
> I will remove the WARN_ONCE, and place a comment in its place:
> 
> /*
>  * the memory area holding the microcode update data must be 16-byte
>  * aligned.  This is supposed to be guaranteed by kmalloc().
>  */

So this makes this comment pretty useless as it doesn't do anything
about the case where 16-byte alignment gets violated. Actually I was
expecting something else:

* you either write down *why* kmalloc guarantees alignment. From a quick
look it might but it might not, hint

#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long long)

* or you actually go and fix this by making sure all memory in the intel
loader is 16-byte aligned. Maybe a loader-specific kmalloc wrapper,
something which allocates a bit more and then aligns it properly, and so
on...

But simply adding a comment which doesn't do anything to solve the
situation doesn't make a lot of sense. And more importantly, doesn't
solve the situation.

-- 
Regards/Gruss,
    Boris.

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