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

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Message-ID: <1360357636.18083.19.camel@x230.lan>
Date:	Fri, 8 Feb 2013 21:07:21 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	Kees Cook <keescook@...omium.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	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 Fri, 2013-02-08 at 13:02 -0800, Kees Cook wrote:

> I don't find it unreasonable to drop all caps and lose access to
> sensitive things. :) That's sort of the point, really. I think a cap
> is the best match. It seems like it should either be a cap or a
> namespace flag, but the latter seems messy.

Yeah, I think it's an expected outcome, but it means that if (say) qemu
drops privileges, qemu can no longer access PCI resources - even on
non-secure boot systems. That breaks existing userspace.