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Date:   Tue, 26 Mar 2019 13:54:40 +0000
To:     Daniel Borkmann <daniel@iogearbox.net>
From:   Jordan Glover <Golden_Miller83@protonmail.ch>
Cc:     Stephen Hemminger <stephen@networkplumber.org>,
        Matthew Garrett <matthewgarrett@google.com>,
        "jmorris@namei.org" <jmorris@namei.org>,
        "linux-security-module@vger.kernel.org" 
        <linux-security-module@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dhowells@redhat.com" <dhowells@redhat.com>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Chun-Yi Lee <jlee@suse.com>, Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Will Drewry <wad@chromium.org>
Reply-To: Jordan Glover <Golden_Miller83@protonmail.ch>
Subject: Re: [PATCH 23/27] bpf: Restrict kernel image access functions when the kernel is locked down
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On Tuesday, March 26, 2019 12:00 AM, Daniel Borkmann <daniel@iogearbox.net>=
 wrote:

> On 03/26/2019 12:42 AM, Stephen Hemminger wrote:
>
> > On Mon, 25 Mar 2019 15:09:50 -0700
> > Matthew Garrett matthewgarrett@google.com wrote:
> >
> > > From: David Howells dhowells@redhat.com
> > > There are some bpf functions can be used to read kernel memory:
> > > bpf_probe_read, bpf_probe_write_user and bpf_trace_printk. These allo=
w
> > > private keys in kernel memory (e.g. the hibernation image signing key=
) to
> > > be read by an eBPF program and kernel memory to be altered without
> > > restriction.
>
> I'm not sure where 'kernel memory to be altered without restriction' come=
s
> from, but it's definitely a wrong statement.
>
> > > Completely prohibit the use of BPF when the kernel is locked down.
>
> In which scenarios will the lock-down mode be used? Mostly niche? I'm ask=
ing
> as this would otherwise break a lot of existing stuff ... I'd prefer you =
find
> a better solution to this than this straight -EPERM rejection.


AFAIK this change breaks IPAddressAllow/IPAddressDeny usage in systemd serv=
ices
which makes them LESS secure.

https://www.freedesktop.org/software/systemd/man/systemd.resource-control.h=
tml
https://github.com/systemd/systemd/blob/04d7ca022843913fba5170c40be07acf2ab=
5902b/README#L96

Jordan