linux-kernel - Re: [PATCH 1/5 v2] PM / hibernate: Create snapshot keys handler

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Date:   Fri, 18 Jan 2019 16:33:48 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Stephan Mueller <smueller@...onox.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "Lee, Chun-Yi" <joeyli.kernel@...il.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        LKML <linux-kernel@...r.kernel.org>, linux-pm@...r.kernel.org,
        keyrings@...r.kernel.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Chen Yu <yu.c.chen@...el.com>,
        Oliver Neukum <oneukum@...e.com>,
        Ryan Chen <yu.chen.surf@...il.com>,
        David Howells <dhowells@...hat.com>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH 1/5 v2] PM / hibernate: Create snapshot keys handler

On Fri, Jan 11, 2019 at 07:28:58AM -0800, James Bottomley wrote:
> On Fri, 2019-01-11 at 16:02 +0200, Jarkko Sakkinen wrote:
> > On Tue, Jan 08, 2019 at 05:43:53PM -0800, Andy Lutomirski wrote:
> > > (Also, do we have a sensible story of how the TPM interacts with
> > > hibernation at all?  Presumably we should at least try to replay
> > > the PCR operations that have occurred so that we can massage the
> > > PCRs into the same state post-hibernation.  Also, do we have any
> > > way for the kernel to sign something with the TPM along with an
> > > attestation that the signature was requested *by the
> > > kernel*?  Something like a sub-hierarchy of keys that the kernel
> > > explicitly prevents userspace from accessing?)
> > 
> > Kernel can keep it is own key hierarchy in memory as TPM2 chips allow
> > to offload data in encrypted form and load it to TPM when it needs to
> > use it.
> > 
> > The in-kernel resource manager that I initiated couple years ago
> > provides this type of functionality.
> 
> Actually, the resource manager only keeps volatile objects separated
> when in use not when offloaded.  The problem here is that the object
> needs to be persisted across reboots, so either it gets written to the
> NV area, bypassing the resource manager and making it globally visible
> or it has to get stored in TPM form in the hibernation image, meaning
> anyone with access to the TPM who can read the image can extract and
> load it. Further: anyone with access to the TPM can create a bogus
> sealed key and encrypt a malicious hibernation image with it.  So there
> are two additional problems
> 
>    1. Given that the attacker may have access to the binary form of the
>       key, can we make sure only the kernel can get it released?
>    2. How do we prevent an attacker with access to the TPM from creating a
>       bogus sealed key?
> 
> This is why I was thinking localities.

Why you would want to go for localities and not seal to PCRs?

/Jarkko