linux-kernel - Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary physical addresses

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Message-ID: <4E0DEF2C.3040504@zytor.com>
Date:	Fri, 01 Jul 2011 09:00:44 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Petr Tesarik <ptesarik@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Luck <tony.luck@...el.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
 physical addresses

On 07/01/2011 08:36 AM, Ingo Molnar wrote:
> 
> So we could kill multiple birds with the same stone here:
> 
>  - remove various ugly uses of /dev/mem (including the rootkit usage),
>    with or without strict-devmem
> 
>  - extending it to above-4G for inspection purposes
> 
>  - allowing to kill /dev/mem access runtime similar to the 
>    disable_modules lock-down killswitch, for the so inclined.
> 
> Would you be interested in modifying your patch-set in such a 
> fashion?
> 

There is another use that I have looked at, as well: for testing
purposes, it would be extremely good to be able to dirty and/or flush an
arbitrary physical cache line for testing purposes.

This is very very similar to /dev/mem usage -- access to an arbitrary
chunk of memory -- and a fully enabled /dev/mem can of course support
this use (just mmap the page with the relevant cache line).  However, it
could also be a separate device which could have looser permissions than
/dev/mem; or a set of ioctls on /dev/mem with a separate kill switch,
because no data would ever be have modified or returned to user space.

Either way, though, we found that it would share a lot of code with the
/dev/mem implementation, and as such fixing up the underlying machinery
is the sanest way to upstream this.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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