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

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Date:	Wed, 13 Feb 2013 05:39:22 +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 Tue, 2013-02-12 at 16:48 -0800, H. Peter Anvin wrote:

> OK... what none of this gets into:
> 
> Why should CAP_RAWIO be allowed on a secure boot system, when there are
> 2^n known ways of compromise a system with CAP_RAWIO?

CAP_SYS_RAWIO seems to have ended up being a catchall of "Maybe someone
who isn't entirely root should be able to do this", and not everything
it covers is equivalent to being able to compromise the running kernel.
I wouldn't argue with the idea that maybe we should just reappraise most
of the current uses of CAP_SYS_RAWIO, but removing capability checks
from places that currently have them seems like an invitation for
userspace breakage.