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

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Message-ID: <5115A4CC.3080102@zytor.com>
Date:	Fri, 08 Feb 2013 17:22:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matthew Garrett <matthew.garrett@...ula.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 02/08/2013 03:26 PM, Matthew Garrett wrote:
> 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.
> 

You don't have to build the kernel twice to exclude a loadable module.

	-hpa

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