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

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Message-ID: <511BDF0F.2000005@zytor.com>
Date:	Wed, 13 Feb 2013 10:44:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Garrett <matthew.garrett@...ula.com>
CC:	Casey Schaufler <casey@...aufler-ca.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 02/13/2013 09:56 AM, Matthew Garrett wrote:
> 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.
>

So people have piggybacked complete inappropriate junk onto 
CAP_SYS_RAWIO.  Great.  What the hell do we do now?  We can't break 
apart CAP_SYS_RAWIO because we don't have hierarchical capabilities.

We thus have a bunch of unpalatable choices, **all of which are wrong**.

This, incidentally, is *exactly* the reason I object to 
CAP_COMPROMISE_KERNEL as well... it describes a usage model, not a resource.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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