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Message-ID: <Y8tcEtr8Kl3p4qtA@kernel.org>
Date: Sat, 21 Jan 2023 03:29:22 +0000
From: Jarkko Sakkinen <jarkko@...nel.org>
To: James Bottomley <jejb@...ux.ibm.com>
Cc: Matthew Garrett <mgarrett@...ora.tech>,
William Roberts <bill.c.roberts@...il.com>,
Evan Green <evgreen@...omium.org>,
linux-kernel@...r.kernel.org, corbet@....net,
linux-integrity@...r.kernel.org,
Eric Biggers <ebiggers@...nel.org>, gwendal@...omium.org,
dianders@...omium.org, apronin@...omium.org,
Pavel Machek <pavel@....cz>, Ben Boeckel <me@...boeckel.net>,
rjw@...ysocki.net, Kees Cook <keescook@...omium.org>,
dlunev@...gle.com, zohar@...ux.ibm.com, linux-pm@...r.kernel.org,
Matthew Garrett <mjg59@...gle.com>,
Jason Gunthorpe <jgg@...pe.ca>, Peter Huewe <peterhuewe@....de>
Subject: Re: [PATCH v5 03/11] tpm: Allow PCR 23 to be restricted to
kernel-only use
On Sat, Jan 14, 2023 at 09:55:37AM -0500, James Bottomley wrote:
> On Tue, 2023-01-03 at 13:10 -0800, Matthew Garrett wrote:
> > On Tue, Jan 3, 2023 at 1:05 PM William Roberts
> > <bill.c.roberts@...il.com> wrote:
> >
> > > What's the use case of using the creation data and ticket in this
> > > context? Who gets the creationData and the ticket?
> > > Could a user supplied outsideInfo work? IIRC I saw some patches
> > > flying around where the sessions will get encrypted and presumably
> > > correctly as well. This would allow the transfer of that
> > > outsideInfo, like the NV Index PCR value to be included and
> > > integrity protected by the session HMAC.
> >
> > The goal is to ensure that the key was generated by the kernel. In
> > the absence of the creation data, an attacker could generate a
> > hibernation image using their own key and trick the kernel into
> > resuming arbitrary code. We don't have any way to pass secret data
> > from the hibernate kernel to the resume kernel, so I don't think
> > there's any easy way to do it with outsideinfo.
>
> Can we go back again to why you can't use locality? It's exactly
> designed for this since locality is part of creation data. Currently
> everything only uses locality 0, so it's impossible for anyone on Linux
> to produce a key with anything other than 0 in the creation data for
> locality. However, the dynamic launch people are proposing that the
> Kernel should use Locality 2 for all its operations, which would allow
> you to distinguish a key created by the kernel from one created by a
> user by locality.
>
> I think the previous objection was that not all TPMs implement
> locality, but then not all laptops have TPMs either, so if you ever
> come across one which has a TPM but no locality, it's in a very similar
> security boat to one which has no TPM.
Kernel could try to use locality 2 and use locality 0 as fallback.
BR, Jarkko
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