Re: [PATCH 06/14] Pramfs: Include files

From: Marco <marco.stornelli@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "David Woodhouse" <dwmw2@infradead.org>,
	"Jörn Engel" <joern@lazybastard.org>,
	"Sam Ravnborg" <sam@ravnborg.org>,
	"Tim Bird" <tim.bird@am.sony.com>,
	"Chris Simmonds" <chris@2net.co.uk>,
	"Linux FS Devel" <linux-fsdevel@vger.kernel.org>,
	"Linux Embedded" <linux-embedded@vger.kernel.org>,
	"Linux Kernel" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 06/14] Pramfs: Include files
Date: Wed, 24 Jun 2009 18:49:41 +0200	[thread overview]
Message-ID: <4A425925.7000601@gmail.com> (raw)
In-Reply-To: <200906241730.37151.arnd@arndb.de>

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