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

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Date:	Wed, 13 Feb 2013 09:51:13 -0800
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Matthew Garrett <matthew.garrett@...ula.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 2/13/2013 9:26 AM, Matthew Garrett wrote:
> On Wed, 2013-02-13 at 09:20 -0800, H. Peter Anvin wrote:
>
>> Problem:
>>
>> Someone adds SYS_CAP_RAWIO to some places it definitely does not
>> belong.
>>
>> Solution:
>>
>> Break all the *appropriate* (as defined)uses of SYS_CAP_RAWIO?
> Problem:
>
> CAP_SYS_RAWIO has been used in a bunch of arguably inappropriate places.
> Removing CAP_SYS_RAWIO from the set of possible capabilities on a system
> will prevent userspace from doing things that userspace should be
> permitted to do. Removing CAP_SYS_RAWIO from the places that it
> currently exists will allow userspace to do too much. Replacing
> CAP_SYS_RAWIO with CAP_SYS_ADMIN will prevent userspace from doing
> things that it can currently do.
>
> Solution:
>
> 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.

If you tried to "fix" CAP_SYS_RAWIO and/or CAP_SYS_ADMIN you'd end
up with hundreds of capabilities.

Your particular problem is *not* so important that you get a
capability all to yourself.


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