linux-kernel - Re: [PATCH] x86: introduce /dev/mem restrictions with a config option

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Date:	Thu, 31 Jan 2008 17:53:04 +0100 (CET)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	linux-kernel@...r.kernel.org, davej@...hat.com, mingo@...e.hu,
	tglx@...x.de, hpa@...or.com
Subject: Re: [PATCH] x86: introduce /dev/mem restrictions with a config option


On Jan 30 2008 12:48, Arjan van de Ven wrote:
>Subject: [PATCH] x86: introduce /dev/mem restrictions with a config option
>
>This patch introduces a restriction on /dev/mem: Only non-memory can be
>read or written unless the newly introduced config option is set.

Would not it be nicer to add a /dev/pcimem that implements the given 
restrictive semantics?

Maybe it's just wishful thinking, but I am dreaming of an unprivileged 
X, and /dev/pcimem (owned by an 'x11' user or so) would be a step in 
that direction.

>The X server needs access to /dev/mem for the PCI space, but it doesn't need
>access to memory; both the file permissions and SELinux permissions of /dev/mem
>just make X effectively super-super powerful. With the exception of the
>BIOS area, there's just no valid app that uses /dev/mem on actual memory.

And so I could even get rid of /dev/mem.

>People who want to use /dev/mem for kernel debugging can enable the config
>option.

With a pcimem, kernel people would not need to reconfig the kernel, just 
create/delete the node as they wish.
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