linux-kernel - Re: [PATCH 2/2] x86: Allow disabling of sys_iopl, sys

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Message-ID: <20110715105557.7cb3dfcc@lxorguk.ukuu.org.uk>
Date:	Fri, 15 Jul 2011 10:55:57 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Mike Waychison <mikew@...gle.com>
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86: Allow disabling of sys_iopl, sys_ioperm

> > So lets turn the question around a moment - what breaks if you simply
> > take CAP_SYS_RAWIO away from everything ?
> >
> 
> Alright, I see your point.   ISTR that CAP_SYS_RAWIO was required for
> accessing block devices directly, but this doesn't seem to be the
> case.

Its needed for certain kinds of command issue (raw commands) but not I
believe raw block I/O

> I think the approach I'll try next is to try and drop it with
> PR_CAPBSET_DROP from early userspace's init.
> 
> Any other vectors you would suggest to keep the kiddies away?

/dev/mem /dev/kmem (which do have options to clamp down on)
module loading you have down

GPU if you don't need any graphics. Not so much because its a specific
threat area but because its a large exposure.

For media there are exploit paths to consider where an attacker rewrites
the boot media and reboots. If you need raw disk I/O those are a spot
harder to mend.

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