linux-kernel - Re: Linux Firmware Signing

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Date:	Tue, 1 Sep 2015 20:08:35 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	David Woodhouse <dwmw2@...radead.org>,
	David Howells <dhowells@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Roberts, William C" <william.c.roberts@...el.com>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"james.l.morris@...cle.com" <james.l.morris@...cle.com>,
	"serge@...lyn.com" <serge@...lyn.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	Eric Paris <eparis@...isplace.org>,
	SE Linux <selinux@...ho.nsa.gov>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	"Schaufler, Casey" <casey.schaufler@...el.com>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Jones <pjones@...hat.com>, Takashi Iwai <tiwai@...e.de>,
	Ming Lei <ming.lei@...onical.com>, Joey Lee <jlee@...e.de>,
	Vojtěch Pavlík <vojtech@...e.com>,
	Kyle McMartin <kyle@...nel.org>,
	Seth Forshee <seth.forshee@...onical.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Johannes Berg <johannes@...solutions.net>,
	Julia Lawall <julia.lawall@...6.fr>,
	Jay Schulist <jschlst@...ba.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: Linux Firmware Signing

On Tue, Sep 1, 2015 at 4:43 PM, Luis R. Rodriguez <mcgrof@...e.com> wrote:
> On Mon, Aug 31, 2015 at 10:18:55AM -0400, Mimi Zohar wrote:
>> > > eBPF/seccomp
>
> OK I knew nothing about this but I just looked into it, here are my notes:
>
>   * old BPF - how far do we want to go? This goes so far as to parsing
>     user passed void __user *arg data through ioctls which typically
>     gets copy_from_user()'d and eventually gets BPF_PROG_RUN().
>
>   * eBPF:
>                              seccomp() & prctl_set_seccomp()
>                                         |
>                                         V
>                              do_seccomp()
>                                         |
>                                         V
>                              seccomp_set_mode_filter()
>                                         |
>                                         V
>                              seccomp_prepare_user_filter()
>                                         |
>                                         V
>         bpf_prog_create_from_user() (seccomp) \
>         bpf_prog_create()                      > bpf_prepare_filter()
>         sk_attach_filter()                    /
>
>     All approaches come from user passed data, nothing fd based.
>
>     For both old BPF and eBPF then:
>
>     If we wanted to be paranoid I suppose the Machine Owner Key (MOK)
>     Paul had mentioned up could be used to vet for passed filters, or
>     a new interface to enable fd based filters. This really would limit
>     the dynamic nature of these features though.
>
>     eBPF / secccomp would not be the only place in the kernel that would have
>     issues with user passed data, we have tons of places the same applies so
>     implicating the old BPF / eBPF / seccomp approaches can easily implicate
>     many other areas of the kernel, that's pretty huge but from the looks of
>     it below you seem to enable that to be a possibility for us to consider.

At the time (LSS 2014?) I argued that seccomp policies come from
binaries, which are already being measured. And that policies only
further restrict a process, so there seems to be to be little risk in
continuing to leave them unmeasured.

-Kees

-- 
Kees Cook
Chrome OS Security
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