Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3537521837
MIME-Version: 1.0
In-Reply-To: <20180403154156.f37wrzjhuvijzi2i@ast-mbp.dhcp.thefacebook.com>
References: <4136.1522452584@warthog.procyon.org.uk> <alpine.LRH.2.21.1803311145180.7769@namei.org>
 <186aeb7e-1225-4bb8-3ff5-863a1cde86de@kernel.org> <30459.1522739219@warthog.procyon.org.uk>
 <CALCETrUFOdrH5ShCCd8yguGjC2NtG8fJY7AW26HH467-02UVGA@mail.gmail.com> <20180403154156.f37wrzjhuvijzi2i@ast-mbp.dhcp.thefacebook.com>
From:   Andy Lutomirski <luto@kernel.org>
Date:   Tue, 3 Apr 2018 09:26:26 -0700
Message-ID: <CALCETrX3D3jrr=Vq70H+ttdCKSevU-cC-cvZrfaoahEQoO7wzA@mail.gmail.com>
Subject: Re: [GIT PULL] Kernel lockdown for secure boot
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        David Howells <dhowells@redhat.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        James Morris <jmorris@namei.org>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Matthew Garrett <mjg59@google.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Justin Forbes <jforbes@redhat.com>,
        linux-man <linux-man@vger.kernel.org>, joeyli <jlee@suse.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        linux-efi <linux-efi@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Apr 3, 2018 at 8:41 AM, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
> On Tue, Apr 03, 2018 at 08:11:07AM -0700, Andy Lutomirski wrote:
>> >
>> >> "bpf: Restrict kernel image access functions when the kernel is locked down":
>> >> This patch just sucks in general.
>> >
>> > Yes - but that's what Alexei Starovoitov specified.  bpf kind of sucks since
>> > it gives you unrestricted access to the kernel.
>>
>> bpf, in certain contexts, gives you unrestricted access to *reading*
>> kernel memory.  bpf should, under no circumstances, let you write to
>> the kernel unless you're using fault injection or similar.
>>
>> I'm surprised that Alexei acked this patch.  If something like XDP or
>> bpfilter starts becoming widely used, this patch will require a lot of
>> reworking to avoid breaking standard distros.
>
> my understanding was that this lockdown set attemps to disallow _reads_
> of kernel memory from anything, so first version of patch was adding
> run-time checks for bpf_probe_read() which is no-go
> and without this helper the bpf for tracing is losing a lot of its power,
> so the easiest is to disable it all.

Fair enough.

> I think lockdown suppose to disable xdp, bpfilter, nflog, raw sockets + pcap too
> otherwise even cap_net_admin can see traffic coming into host.
> Similarly kprobe, perf_event, ftrace should be off as well?
>

I'm reasonably sure that lockdown is not intended to be this far
reaching.  cap_net_admin can see traffic coming into the host, and I
don't think lockdown is intended to change that.

David, I think this is exactly why you need to define what "lockdown"
means.  As it stands, the best argument I've seen involves
"blacklisting", but that's a political thing and almost no one
involved has any ability to evaluate it.  Right now there's a series
of patches that check for "lockdown" and seem to disable things that
make someone uncomfortable.  That's not a good way to design a
security feature.