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

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Date:	Fri, 1 Jul 2011 16:46:41 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Petr Tesarik <ptesarik@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...or.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


* Christoph Hellwig <hch@...radead.org> wrote:

> On Fri, Jul 01, 2011 at 04:37:35PM +0200, Ingo Molnar wrote:
>
> > After initial modules have loaded i essentially disable crash.ko 
> > via /proc/sys/kernel/modules_disabled so rootkits have to work a 
> > bit harder than that.
> 
> Not sure for fedora as I don'[t have a kernel tree at hand right 
> now, but for x86 systems at least RHEL6 has the module built in. 
> [...]

Fedora Rawhide has it modular:

 # grep CRASH /boot/config-2.6.38-0.rc7.git2.3.fc16.x86_64
 CONFIG_CRASH=m

 # rpm -ql kernel-2.6.38-0.rc7.git2.3.fc16.x86_64 | grep crash
 /lib/modules/2.6.38-0.rc7.git2.3.fc16.x86_64/kernel/drivers/char/crash.ko

> [...]  Either way we'll need some way to support crash properly in 
> mainline, preferably in a boot-time opt-in way. [...]

Yes, boot-time opt-in was what i suggested.

> [...] I'd tend slightly toward optionally enabling /dev/mem for it 
> instead of a separate driver, but if people prefer a different 
> route I'm fine, too.

No, sharing the driver is perfectly fine and sane as long as this 
weird usage is not enabled widely.

> Note that for normal crash usage read only access is just fine.

That's true as well. Petr?

Thanks,

	Ingo
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