linux-kernel - Re: Turn CONFIG_STRICT_DEVMEM in sysctl dev.mem.restricted

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Date:	Sun, 16 Nov 2008 16:09:05 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Bernhard Walle <bwalle@...e.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	crash-utility@...hat.com
Subject: Re: Turn CONFIG_STRICT_DEVMEM in sysctl dev.mem.restricted

> because it can load kernel modules?
> or because it can bypass the iommu?

It has iopl, firmware loading, ioperm, raw disk I/O, mknod, module loading
etc etc.. 

> the point of the /dev/mem restrictions is to not allow things you know
> you don't need, while still allowing X to function where it can access
> the crap it does. Now in Bernhard's case he DOES need them, so he
> shouldn't use the restrictions.

I know what the point is, but it doesn't actually implement any
meaningful restriction to achieve that result, so it is worthless junk.

> > There are proper ways to deal with X, modern video cards and modern
> > security models. They involve using framebuffer mappings off the PCI
> > device node itself and DRI.
> > 
> when X has this for all hw that matters /dev/mem could go away for the
> people who then no longer have any need for it.

Why should it go away ? It's a matter of file permissions and security
rules as to who can access it. Trying to make it go away is just more
fake-security crap.

Alan
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