From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: Re: [PATCH 20/24] bpf: Restrict kernel image access functions when the kernel is locked down Date: Thu, 6 Apr 2017 08:29:09 -0400 Message-ID: <20170406122907.GA53880@ast-mbp.thefacebook.com> References: <149142326734.5101.4596394505987813763.stgit@warthog.procyon.org.uk> <149142344547.5101.4518618716303032193.stgit@warthog.procyon.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, gnomes@lxorguk.ukuu.org.uk, netdev@vger.kernel.org, Chun-Yi Lee , linux-security-module@vger.kernel.org, keyrings@vger.kernel.org, gregkh@linuxfoundation.org, matthew.garrett@nebula.com To: David Howells Return-path: Received: from mail-yb0-f194.google.com ([209.85.213.194]:33743 "EHLO mail-yb0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754077AbdDFM3O (ORCPT ); Thu, 6 Apr 2017 08:29:14 -0400 Content-Disposition: inline In-Reply-To: <149142344547.5101.4518618716303032193.stgit@warthog.procyon.org.uk> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Apr 05, 2017 at 09:17:25PM +0100, David Howells wrote: > From: Chun-Yi Lee > > 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. Prohibit those functions when the kernel is > locked down. > > Signed-off-by: Chun-Yi Lee > Signed-off-by: David Howells > cc: netdev@vger.kernel.org > --- > > kernel/trace/bpf_trace.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index cee9802cf3e0..7fde851f207b 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -65,6 +65,11 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr) > { > int ret; > > + if (kernel_is_locked_down()) { > + memset(dst, 0, size); > + return -EPERM; > + } this will obviously break the program. How about disabling loading tracing programs during the lockdown completely? Also is there a description of what this lockdown trying to accomplish? The cover letter is scarce in details.