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

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Message-ID: <CACdnJusbi1jB+G0wMcj43wNik9Fiv3QCc8v30ztrFWg5-P-0iQ@mail.gmail.com>
Date:   Thu, 28 Mar 2019 11:07:58 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     James Morris <jmorris@...ei.org>
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 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.

> 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)?