netdev - Re: [PATCH 23/27] bpf: Restrict kernel image access functions when the kernel is locked down

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Message-ID: <alpine.LRH.2.21.1903290621350.1769@namei.org>
Date:   Fri, 29 Mar 2019 06:23:30 +1100 (AEDT)
From:   James Morris <jmorris@...ei.org>
To:     Matthew Garrett <mjg59@...gle.com>
cc:     Andy Lutomirski <luto@...nel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Linux API <linux-api@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        Chun-Yi Lee <jlee@...e.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 23/27] bpf: Restrict kernel image access functions when
 the kernel is locked down

On Thu, 28 Mar 2019, Matthew Garrett wrote:

> On Wed, Mar 27, 2019 at 8:15 PM James Morris <jmorris@...ei.org> wrote:
> > OTOH, this seems like a combination of mechanism and policy. The 3 modes
> > are a help here, but I wonder if they may be too coarse grained still,
> > e.g. if someone wants to allow a specific mechanism according to their own
> > threat model and mitigations.
> 
> In general the interfaces blocked by these patches could also be
> blocked with an LSM, and I'd guess that people with more fine-grained
> requirements would probably take that approach.

So... I have to ask, why not use LSM for this in the first place?

Either with an existing module or perhaps a lockdown LSM?

> 
> > Secure boot gives you some assurance of the static state of the system at
> > boot time, and lockdown is certainly useful (with or without secure boot),
> > but it's not a complete solution to runtime kernel integrity protection by
> > any stretch of the imagination.  I'm concerned about it being perceived as
> > such.
> 
> What do you think the functionality gaps are in terms of ensuring
> kernel integrity (other than kernel flaws that allow the restrictions
> to be bypassed)?

I don't know of any non-flaw gaps.

-- 
James Morris
<jmorris@...ei.org>