linux-kernel - Re: [PATCH V34 23/29] bpf: Restrict bpf when kernel lockdown is in confidentiality mode

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Message-ID: <CACdnJuu20Rsb-9XAcTR5Q9RJ5wY7ATazS7dLgDODH+YSZU50Tg@mail.gmail.com>
Date:   Mon, 24 Jun 2019 13:15:44 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...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>, Jann Horn <jannh@...gle.com>,
        bpf@...r.kernel.org
Subject: Re: [PATCH V34 23/29] bpf: Restrict bpf when kernel lockdown is in
 confidentiality mode

On Mon, Jun 24, 2019 at 1:09 PM Andy Lutomirski <luto@...nel.org> wrote:

> I'm confused.  I understand why we're restricting bpf_probe_read().
> Why are we restricting bpf_probe_write_user() and bpf_trace_printk(),
> though?

Hmm. I think the thinking here was around exfiltration mechanisms, but
if the read is blocked then that seems less likely. This seems to
trace back to http://kernsec.org/pipermail/linux-security-module-archive/2017-October/003545.html
- Joey, do you know the reasoning here?