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

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Date:	Thu, 31 Jan 2008 15:04:28 +0100
From:	devzero@....de
To:	arjan@...radead.org
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: introduce /dev/mem restrictions with a config option

nice !

did you think about some boot-time param , e.g. "insecure-devmem" or something like that?

recompiling kernel is time consuming.....

From: Arjan van de Ven <arjan@...ux.intel.com>
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.

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.
Other popular users of /dev/mem are rootkits and the like.
(note: mmap access of memory via /dev/mem was already not allowed since
a really long time)

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

The restrictions of this patch have been in the Fedora and RHEL kernels for
at least 4 years without any problems.

Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
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