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

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Message-ID: <1360776399.18083.39.camel@x230.lan>
Date:	Wed, 13 Feb 2013 17:26:39 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	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 09:20 -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.