linux-kernel - Re: [PATCH V3 03/11] x86: Lock down IO port access when module security is enabled

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Message-ID: <1378353524.13193.26.camel@x230>
Date:	Thu, 5 Sep 2013 03:58:45 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	"keescook@...omium.org" <keescook@...omium.org>
Subject: Re: [PATCH V3 03/11] x86: Lock down IO port access when module
 security is enabled

On Wed, 2013-09-04 at 20:52 -0700, H. Peter Anvin wrote:
> On 09/03/2013 04:50 PM, Matthew Garrett wrote:
> > IO port access would permit users to gain access to PCI configuration
> > registers, which in turn (on a lot of hardware) give access to MMIO register
> > space. This would potentially permit root to trigger arbitrary DMA, so lock
> > it down by default.
> > 
> > Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
> 
> Seriously... just deny CAP_SYS_RAWIO to any system in secure mode.

No. CAP_SYS_RAWIO blocks things that we don't want blocked (x86
microcode updates, various disk ioctls, *device firmware uploads* and a
few others) - the semantics just don't match. We could relax those
permissions, but then we'd potentially break someone else's security
considerations.

-- 
Matthew Garrett <matthew.garrett@...ula.com>