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

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Message-ID: <CAGXu5jKo2PfMBO4A0ZgQcrPuj8OHNaff+CjAesOAWkZc0vB9+Q@mail.gmail.com>
Date:	Fri, 8 Feb 2013 13:02:15 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Matthew Garrett <matthew.garrett@...ula.com>
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, Feb 8, 2013 at 12:34 PM, Matthew Garrett
<matthew.garrett@...ula.com> wrote:
> On Fri, 2013-02-08 at 12:28 -0800, Kees Cook wrote:
>
>> Maybe a capability isn't the right way to go, I'm not sure. I'll leave
>> that to Matthew. Whatever the flag, it should be an immutable state of
>> the boot. Though, it probably makes sense as a cap just so that
>> non-secure-boot systems can still remove it from containers, etc.
>
> There was interest in ensuring that this wasn't something special-cased
> to UEFI Secure Boot, so using a capability seemed like the most
> straightforward way - it's fundamentally a restriction on what an
> otherwise privileged user is able to do, so it seemed like it fit the
> model. But I'm not wed to it in the slightest, and in fact it causes
> problems for some userspace (anything that drops all capabilities
> suddenly finds itself unable to do something that it expects to be able
> to do), so if anyone has any suggestions for a better approach…

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.

-Kees

--
Kees Cook
Chrome OS Security
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