linux-kernel - Re: [PATCH -tip] kmemcheck: fix crash in PnP BIOS calls

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Message-ID: <20081005191555.5715da29@lxorguk.ukuu.org.uk>
Date:	Sun, 5 Oct 2008 19:15:55 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip] kmemcheck: fix crash in PnP BIOS calls

> It turns out that BIOS calls are made with a different code segment. So
> when kmemcheck tries to dereference the EIP/RIP (using the kernel data
> segment register), we get the unhandled page fault.
> 
> I think we can solve this by verifying (in the page fault handler) that
> the faulting code is using the kernel CS.

That isn't an entirely safe assumption and some services such as BIOS32
are 32bit. Would it be better wrap BIOS calls with a kmemcheck wrapper
which changes the way kmemcheck works/dumps stuff and also gives you a
hook after BIOS calls to do stuff like corruption scans or change
detection on kernel pages ?

Alan
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