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

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Message-ID: <1360366012.18083.21.camel@x230.lan>
Date:	Fri, 8 Feb 2013 23:26:53 +0000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	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 Sat, 2013-02-09 at 00:06 +0100, Borislav Petkov wrote:
> On Fri, Feb 08, 2013 at 02:30:52PM -0800, H. Peter Anvin wrote:
> > Also, keep in mind that there is a very simple way to deny MSR access
> > completely, which is to not include the driver in your kernel (and not
> > allow module loading, but if you can load modules you can just load a
> > module to muck with whatever MSR you want.)
> 
> I was contemplating that too. What is the use case of having
> msr.ko in a secure boot environment? Isn't that an all-no-tools,
> you-can't-do-sh*t-except-what-you're-explicitly-allowed-to environment which
> simply doesn't need to write MSRs in the first place?

Well, sure, distributions could build every kernel twice. That seems a
little excessive, though.