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From:   Evan Green <evgreen@chromium.org>
Date:   Tue, 17 May 2022 10:34:05 -0700
Message-ID: <CAE=gft6V6RLc-d4AOuRUVU2u1jMGghDRSrFqiCqMCLxemui8Pw@mail.gmail.com>
Subject: Re: [PATCH 00/10] Encrypted Hibernation
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Pavel Machek <pavel@ucw.cz>, LKML <linux-kernel@vger.kernel.org>,
        Matthew Garrett <mgarrett@aurora.tech>,
        Daniil Lunev <dlunev@google.com>, zohar@linux.ibm.com,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        linux-integrity@vger.kernel.org, Jonathan Corbet <corbet@lwn.net>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Gwendal Grignou <gwendal@chromium.org>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        Hao Wu <hao.wu@rubrik.com>, James Morris <jmorris@namei.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Len Brown <len.brown@intel.com>,
        Matthew Garrett <matthewgarrett@google.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        "Serge E. Hallyn" <serge@hallyn.com>, axelj <axelj@axis.com>,
        keyrings@vger.kernel.org,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        linux-security-module@vger.kernel.org
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Hi Rafael,

On Tue, May 17, 2022 at 9:06 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Mon, May 9, 2022 at 6:44 PM Evan Green <evgreen@chromium.org> wrote:
> >
> > On Fri, May 6, 2022 at 9:08 AM Pavel Machek <pavel@ucw.cz> wrote:
> > >
> > > Hi!
> > >
> > > > We are exploring enabling hibernation in some new scenarios. However,
> > > > our security team has a few requirements, listed below:
> > > > 1. The hibernate image must be encrypted with protection derived from
> > > >    both the platform (eg TPM) and user authentication data (eg
> > > >    password).
> > > > 2. Hibernation must not be a vector by which a malicious userspace can
> > > >    escalate to the kernel.
> > >
> > > Can you (or your security team) explain why requirement 2. is needed?
> > >
> > > On normal systems, trusted userspace handles kernel upgrades (for example),
> > > so it can escalate to kernel priviledges.
> > >
> >
> > Our systems are a little more sealed up than a normal distro, we use
> > Verified Boot [1]. To summarize, RO firmware with an embedded public
> > key verifies that the kernel+commandline was signed by Google. The
> > commandline includes the root hash of the rootfs as well (where the
> > modules live). So when an update is applied (A/B style, including the
> > whole rootfs), assuming the RO firmware stayed RO (which requires
> > physical measures to defeat), we can guarantee that the kernel,
> > commandline, and rootfs have not been tampered with.
> >
> > Verified boot gives us confidence that on each boot, we're at least
> > starting from known code. This makes it more challenging for an
> > attacker to persist an exploit across reboot. With the kernel and
> > modules verified, we try to make it non-trivial for someone who does
> > manage to gain root execution once from escalating to kernel
> > execution. Hibernation would be one obvious escalation route, so we're
> > hoping to find a way to enable it without handing out that easy
> > primitive.
> >
> > [1] https://www.chromium.org/chromium-os/chromiumos-design-docs/verified-boot/
>
> So I guess this really is an RFC.

Yes, I suppose it is.

>
> Honestly, I need more time to go through this and there are pieces of
> it that need to be looked at other people (like the TPM-related
> changes).

No problem, thanks for the reply to let me know. I expect some back
and forth in terms of what should be hidden behind abstractions and
where exactly things should live. But I wanted to get this out to
upstream as early as I could, just to get initial reactions on the
overall concept and design. Looking forward to hearing your thoughts
when you get a chance, and let me know if there are others I should be
adding that I've missed.

-Evan

>
> Thanks!