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

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Date:   Mon, 25 Mar 2019 16:59:44 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Matthew Garrett <matthewgarrett@...gle.com>
Cc:     jmorris@...ei.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        netdev@...r.kernel.org, Chun-Yi Lee <jlee@...e.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 23/27] bpf: Restrict kernel image access functions when
 the kernel is locked down

On Mon, 25 Mar 2019 16:42:21 -0700
Stephen Hemminger <stephen@...workplumber.org> wrote:

> On Mon, 25 Mar 2019 15:09:50 -0700
> Matthew Garrett <matthewgarrett@...gle.com> wrote:
> 
> > From: David Howells <dhowells@...hat.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 allow
> > 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.
> > 
> > Completely prohibit the use of BPF when the kernel is locked down.
> > 
> > Suggested-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
> > Signed-off-by: David Howells <dhowells@...hat.com>
> > cc: netdev@...r.kernel.org
> > cc: Chun-Yi Lee <jlee@...e.com>
> > cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > Signed-off-by: Matthew Garrett <matthewgarrett@...gle.com>  
> 
> Wouldn't this mean that Seccomp won't work in locked down mode?

Never mind. This is about bpf system call, not locking out all bpf in general.