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

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Message-ID: <511B2EB9.5070406@zytor.com>
Date:	Tue, 12 Feb 2013 22:12:09 -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 02/12/2013 09:39 PM, Matthew Garrett wrote:
> 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.
>

Sounds like you are thinking of CAP_SYS_ADMIN, but I don't really see a 
huge difference between MSRs and I/O control registers... just different 
address spaces.

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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