linux-kernel - Re: [PATCH 06/14] Pramfs: Include files

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Date:	Wed, 24 Jun 2009 18:49:41 +0200
From:	Marco <marco.stornelli@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	David Woodhouse <dwmw2@...radead.org>,
	Jörn Engel <joern@...ybastard.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Tim Bird <tim.bird@...sony.com>,
	Chris Simmonds <chris@...t.co.uk>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Linux Embedded <linux-embedded@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/14] Pramfs: Include files

Arnd Bergmann wrote:
> On Wednesday 24 June 2009, Marco Stornelli wrote:
>>> Actually, reading from /dev/mem is only valid on real RAM. If the nvram
>>> is part of an IO memory mapping, you have to do mmap()+memcpy() rather
>>> than read(). So dd won't do it, but it's still easy to read from user
>>> space.
>> For "security" reasons pram reserve the region of memory with
>> reserve_mem_region_exclusive().....
> 
> That will only prevent other device drivers from stepping on it,
> /dev/mem does not care about mem_region reservations.
> 
> 	Arnd <><
> 

Userland may not map this resource, so /dev/mem and the sysfs MMIO
access will not be allowed. This restriction depends on STRICT_DEVMEM
option. It's true that currently is only implemented in the x86 world.

Marco

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