linux-kernel - Re: unable to mmap /dev/kmem

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Message-ID: <Pine.LNX.4.64.0701191743560.10013@blonde.wat.veritas.com>
Date:	Fri, 19 Jan 2007 17:52:57 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	Nadia Derbey <Nadia.Derbey@...l.net>,
	Franck Bui-Huu <fbuihuu@...il.com>, Andi Kleen <ak@...e.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: unable to mmap /dev/kmem

On Fri, 19 Jan 2007, Arjan van de Ven wrote:
> On Fri, 2007-01-19 at 17:12 +0000, Hugh Dickins wrote:
> > Though so long as /dev/mem support remains, /dev/kmem might as well?
> 
> they're not the same; for a long time, /dev/mem on actual memory
> returned zeros... so you couldn't use it for rootkits ;)
> (that got "fixed" a while ago)

We fixed (or "fixed") the mmap of them both, not to give zeroes on
!PageReserved pages; but read and write were never so restricted.
(Oh, I've said "never" again - expect I'll be humiliated shortly.)
Can't rootkits work as just about as easily through read & write?

Hugh
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