linux-kernel - Re: [PATCH] x86: Lock down MSR writing in secure boot

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Date:	Wed, 13 Feb 2013 17:56:19 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	Casey Schaufler <casey@...aufler-ca.com>
CC:	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] x86: Lock down MSR writing in secure boot

On Wed, 2013-02-13 at 09:51 -0800, Casey Schaufler wrote:
> On 2/13/2013 9:26 AM, Matthew Garrett wrote:
> > Admit that CAP_SYS_RAWIO is fucked up beyond rescue. Add a new
> > capability with well-defined semantics.
> 
> You can't add a new capability where there is an existing capability
> that can be remotely argued to be appropriate.

CAP_SYS_RAWIO can't be argued to be appropriate. It covers a range of
functionality that doesn't permit the running kernel to be modified and
which is required to provide a functional Linux system. Using it would
require redefining its existing usage, which would break existing
userspace.

-- 
Matthew Garrett | mjg59@...f.ucam.org