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From: Matthew Garrett <mjg59@google.com>
To: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Andy Lutomirski <luto@kernel.org>,
	linux-security@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	David Howells <dhowells@redhat.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Network Development <netdev@vger.kernel.org>,
	Chun-Yi Lee <jlee@suse.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH V33 24/30] bpf: Restrict bpf when kernel lockdown is in confidentiality mode
Date: Thu, 27 Jun 2019 16:16:36 -0700
Message-ID: <CACdnJuuG8cR7h9v3pNcBKsxyckAzpKuBJs1GQxsz77jk5DRoQA@mail.gmail.com> (raw)
In-Reply-To: <de8b15eb-ba6c-847a-7435-42742203d4a5@tycho.nsa.gov>

On Thu, Jun 27, 2019 at 1:16 PM Stephen Smalley <sds@tycho.nsa.gov> wrote:
> That would only allow the LSM to further lock down the system above the
> lockdown level set at boot, not grant exemptions for specific
> functionality/interfaces required by the user or by a specific
> process/program. You'd have to boot with lockdown=none (or your
> lockdown=custom suggestion) in order for the LSM to allow anything
> covered by the integrity or confidentiality levels.  And then the kernel
> would be unprotected prior to full initialization of the LSM, including
> policy load.
>
> It seems like one would want to be able to boot with lockdown=integrity
> to protect the kernel initially, then switch over to allowing the LSM to
> selectively override it.

One option would be to allow modules to be "unstacked" at runtime, but
there's still something of a problem here - how do you ensure that
your userland can be trusted to load a new policy before it does so?
If you're able to assert that your early userland is trustworthy
(perhaps because it's in an initramfs that's part of your signed boot
payload), there's maybe an argument that most of the lockdown
integrity guarantees are unnecessary before handoff - just using the
lockdown LSM to protect against attacks via kernel parameters would be
sufficient.

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20190621011941.186255-1-matthewgarrett@google.com>
2019-06-21  1:19 ` Matthew Garrett
2019-06-21  5:22   ` Andy Lutomirski
2019-06-21 20:05     ` Matthew Garrett
2019-06-26 20:22     ` James Morris
2019-06-27  0:57       ` Andy Lutomirski
2019-06-27 14:35         ` Stephen Smalley
2019-06-27 18:06           ` James Morris
2019-06-27 20:16             ` Stephen Smalley
2019-06-27 23:16               ` Matthew Garrett [this message]
2019-06-27 23:23                 ` Andy Lutomirski
2019-06-27 23:27           ` Andy Lutomirski
2019-06-28 18:47             ` Matthew Garrett
2019-06-29 23:47               ` Andy Lutomirski

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