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Date: Fri, 1 Jul 2011 16:46:41 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Christoph Hellwig <hch@infradead.org>
Cc: Petr Tesarik <ptesarik@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        Fenghua Yu <fenghua.yu@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
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        Dave Jones <davej@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 00/10] Enhance /dev/mem to allow read/write of arbitrary
 physical addresses
Message-ID: <20110701144641.GA23272@elte.hu>
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* Christoph Hellwig <hch@infradead.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