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

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Message-ID: <511B33BC.9080307@zytor.com>
Date:	Tue, 12 Feb 2013 22:33:32 -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 10:27 PM, Matthew Garrett wrote:
> On Tue, 2013-02-12 at 22:12 -0800, H. Peter Anvin wrote:
>
>> 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.
>
> Not having CAP_SYS_RAWIO blocks various SCSI commands, for instance.
> These might result in the ability to write individual blocks or destroy
> the device firmware, but do any of them permit modifying the running
> kernel?

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.

And some SCSI driver requires this??!

	-hpa

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

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