linux-kernel - Re: [PATCH RFC] x86: check for and defend against BIOS memory corruption

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Message-ID: <48B82BFD.5030807@zytor.com>
Date:	Fri, 29 Aug 2008 10:03:57 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Hugh Dickins <hugh@...itas.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>, Ingo Molnar <mingo@...e.hu>,
	Rafał Miłecki <zajec5@...il.com>,
	Alan Jenkins <alan-jenkins@...fmail.co.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] x86: check for and defend against BIOS memory corruption

Hugh Dickins wrote:
> 
> hpa introduced the 64k idea, and we've all been repeating it;
> but I've not heard the reasoning behind it.  Is it a fundamental
> addressing limitation within the BIOS memory model?  Or a case
> that Windows treats the bottom 64k as scratch, so BIOS testers
> won't notice if they corrupt it?
> 

I should point out that I have seen one particular bug quite a few times 
poking around with boot loaders: the BIOS accesses memory at an 
otherwise valid address, but with the segment base set to either zero or 
0x400 instead of whatever it should have been.

	-hpa
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