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

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Date:	Wed, 13 Feb 2013 06:41:54 +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 22:33 -0800, H. Peter Anvin wrote:

> That is just batshit crazy.  If you have CAP_SYS_RAWIO you can do iopl() 
> which means you can reprogram your northbridge, at which point you most 
> definitely *can* modify the running kernel.

Well right, that's the point of this patchset - it adds some extra
permission checks to some of the existing CAP_SYS_RAWIO checks.
CAP_SYS_RAWIO hasn't meant "I can perform arbitrary pio and mmio" for
years - it means "I can do things that might maybe break something
somehow". So sure, removing CAP_SYS_RAWIO would give us basically all
the security we want in a secure boot environment, but it would also
block things that we *want* to work.