Re: [PATCH] doc: trusted-encrypted: updates with TEE as a new trust source (update)

[Sumit Garg <sumit.garg@linaro.org>]

Hi Elaine,

On Sat, 16 Jan 2021 at 04:45, Elaine Palmer <erpalmerny@gmail.com> wrote:
>
>
>
> On 1/13/21 4:23 PM, Jarkko Sakkinen wrote:
> > On Tue, Jan 12, 2021 at 10:55:44AM +0530, Sumit Garg wrote:
> >> On Sun, 10 Jan 2021 at 08:46, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> >>> On Mon, Jan 04, 2021 at 06:06:33PM +0530, Sumit Garg wrote:
> >>>> Hi Jarkko, On Fri, 11 Dec 2020 at 13:44, Jarkko Sakkinen
> >>>> <jarkko@kernel.org> wrote:
> >>>>> On Wed, Dec 09, 2020 at 11:42:49AM -0500, Mimi Zohar wrote:
> >>>>>> From: Elaine Palmer <erpalmer@us.ibm.com> Update trusted key
> >>>>>> documentation with additional comparisons between discrete TPMs
> >>>>>> and TEE. Signed-off-by: Elaine Palmer <erpalmer@us.ibm.com>
> >>>>> Right, so OP-TEE is not the same as TEE. I did not know this and
> >>>>> the patch set does not underline this. I re-checked the patches
> >>>>> and none of them say explicitly that OP-TEE is an application
> >>>>> living inside TEE.
> >>>> This patch-set provides a trust source based on generic TEE
> >>>> interface where underlying TEE implementations like OP-TEE
> >>>> (drivers/tee/optee/), AMD TEE (drivers/tee/amdtee/) etc. can easily
> >>>> be hooked up. And this is similar to the TPM interface where
> >>>> underlying TPM implementations like discrete TPM, virtual TPM,
> >>>> firmware TPM etc. can be easily hooked up.
> >>>>> This essentially means that the backend needs to be renamed as
> >>>>> "op_tee".
> >>>> I don't see any need for this, see above.
> >>> Right, TEE is a protocol standard, just like TPM, and OP-TEE is one
> >>> implementation of this interface? I.e. OP-TEE does not define API
> >>> that is hard bound to OP-TEE?
> >> Yes, OP-TEE doesn't define a hard bound client interface API. The
> >> client API is based on TEE client API specification [1] from
> >> GlobalPlatform. [1]
> >> http://globalplatform.org/specs-library/tee-client-api-specification/
> >> -Sumit
> > Thanks, bookmarked. No need for name change. /Jarkko
> This discussion has illustrated that even those of us who live and
> breathe this stuff could use clarification.  Shouldn't we recommend
> that the Trust Source have a hardware root of trust?  We could be
> even more specific.  For example, the documentation could recommend
> that a TPM be evaluated under "TCG Protection Profile for PC Client
> Specific TPM 2.0" or later and a TEE be evaluated under GlobalPlatform
> "TEE Protection Profile v1.3, GPD_SPE_021" or later.  Of course, our
> recommendation would not be a requirement, but it would provide
> guidance for deployment as well as precedent for future Trust Sources.
>

Sure, I will update documentation to mention this as a recommendation.

> I know where I'm getting stuck is on TEEs as a concept vs
> TEEs with specific hardware requirements and interfaces.
> The same applies to TPMs.  There are hardware TPMs that meet
> the protection profile and there are other implementations
> (e.g., vTPMs) that use the same interface, but aren't anchored in
> hardware.

Similar is the case with TEEs which can have varying hardware
realizations. Have a look at "Figure 2-3: Example Hardware
Realizations of TEE" from TEE system architecture specification [1].

[1] https://globalplatform.org/specs-library/tee-system-architecture-v1-2/

>
> I know if I were deploying a server, mobile device, or IoT device, I'd
> want to know exactly what is protecting my keys.  A generic TPM or TEE
> doesn't tell me enough.
>

Agree.

-Sumit

> -Elaine
>
>