linux-hardening - Re: [QUESTION] Full user space process isolation?

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Date:   Mon, 3 Jul 2023 11:47:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Roberto Sassu <roberto.sassu@...weicloud.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Casey Schaufler <casey@...aufler-ca.com>,
        David Howells <dhowells@...hat.com>,
        LuisChamberlain <mcgrof@...nel.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Petr Tesarik <petrtesarik@...weicloud.com>,
        Christoph Hellwig <hch@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, keyrings@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [QUESTION] Full user space process isolation?

On Mon, Jul 03, 2023 at 05:06:42PM +0200, Jann Horn wrote:
> But I'm not convinced that it makes sense to try to draw a security
> boundary between fully-privileged root (with the ability to mount
> things and configure swap and so on) and the kernel - my understanding
> is that some kernel subsystems don't treat root-to-kernel privilege
> escalation issues as security bugs that have to be fixed.

There are certainly arguments to be made about this, but efforts continue
to provide a separation between full-cap uid 0 and kernel memory. LSMs
like Lockdown, IMA, and LoadPin, for example, seek to close these gaps,
and systems are designed with this bright line existing between kernel
and root (e.g. Chrome OS). I'm sure there are gaps in attack surface
coverage, but since work continues on this kind of hardening, I'd hate
to knowingly create new attack surface. Providing uid 0 with kernel
memory access should continue to be mediated by at least Lockdown, and
if there are gaps in coverage, let's get them recorded[1] to be fixed.

-Kees

[1] https://github.com/KSPP/linux/issues

-- 
Kees Cook