Date:   Thu, 3 Nov 2016 21:52:13 +0200
From:   Volodymyr Babchuk <vlad.babchuk@...il.com>
To:     Jens Wiklander <jens.wiklander@...aro.org>
Cc:     "Andrew F. Davis" <afd@...com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>, valentin.manea@...wei.com,
        jean-michel.delorme@...com, emmanuel.michel@...com,
        javier@...igon.com,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        Mark Rutland <mark.rutland@....com>,
        Michal Simek <michal.simek@...inx.com>,
        Rob Herring <robh+dt@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>, Nishanth Menon <nm@...com>,
        broonie@...nel.org
Subject: Re: [PATCH v12 RESEND 0/4] generic TEE subsystem

On 3 November 2016 at 21:35, Jens Wiklander <jens.wiklander@...aro.org> wrote:
> On Mon, Oct 31, 2016 at 01:24:14PM -0500, Andrew F. Davis wrote:
>> On 10/29/2016 04:46 AM, Jens Wiklander wrote:
>> > On Fri, Oct 28, 2016 at 10:43:24AM -0500, Andrew F. Davis wrote:
>> >> On 10/28/2016 05:19 AM, Jens Wiklander wrote:
>> >>> Hi,
>> >>>
>> >>> This patch set introduces a generic TEE subsystem. The TEE subsystem will
>> >>> contain drivers for various TEE implementations. A TEE (Trusted Execution
>> >>> Environment) is a trusted OS running in some secure environment, for
>> >>> example, TrustZone on ARM CPUs, or a separate secure co-processor etc.
>> >>>
>> >>> Regarding use cases, TrustZone has traditionally been used for
>> >>> offloading secure tasks to the secure world. Examples include:
>> >>> - Secure key handling where the OS may or may not have direct access to key
>> >>>   material.
>> >>> - E-commerce and payment technologies. Credentials, credit card numbers etc
>> >>>   could be stored in a more secure environment.
>> >>> - Trusted User Interface (TUI) to ensure that no-one can snoop PIN-codes
>> >>>   etc.
>> >>> - Secure boot to ensure that loaded binaries haven’t been tampered with.
>> >>>   It’s not strictly needed for secure boot, but you could enhance security
>> >>>   by leveraging a TEE during boot.
>> >>> - Digital Rights Management (DRM), the studios provides content with
>> >>>   different resolution depending on the security of the device. Higher
>> >>>   security means higher resolution.
>> >>>
>> >>> A TEE could also be used in existing and new technologies. For example IMA
>> >>> (Integrity Measurement Architecture) which has been in the kernel for quite
>> >>> a while. Today you can enhance security by using a TPM-chip to sign the IMA
>> >>> measurement list. This is something that you also could do by leveraging a
>> >>> TEE.
>> >>>
>> >>> Another example could be in 2-factor authentication which is becoming
>> >>> increasingly more important. FIDO (https://fidoalliance.org) for example
>> >>> are using public key cryptography in their 2-factor authentication standard
>> >>> (U2F). With FIDO, a private and public key pair will be generated for every
>> >>> site you visit and the private key should never leave the local device.
>> >>> This is an example where you could use secure storage in a TEE for the
>> >>> private key.
>> >>>
>> >>> Today you will find a quite a few different out of tree implementations of
>> >>> TEE drivers which tends to fragment the TEE ecosystem and development. We
>> >>> think it would be a good idea to have a generic TEE driver integrated in
>> >>> the kernel which would serve as a base for several different TEE solutions,
>> >>> no matter if they are on-chip like TrustZone or if they are on a separate
>> >>> crypto co-processor.
>> >>>
>> >>> To develop this TEE subsystem we have been using the open source TEE called
>> >>> OP-TEE (https://github.com/OP-TEE/optee_os) and therefore this would be the
>> >>> first TEE solution supported by this new subsystem. OP-TEE is a
>> >>> GlobalPlatform compliant TEE, however this TEE subsystem is not limited to
>> >>> only GlobalPlatform TEEs, instead we have tried to design it so that it
>> >>> should work with other TEE solutions also.
>> >>>
>> >>
>> >> The above is my biggest concern with this whole subsystem, to me it
>> >> still feels very OPTEE specific. As much as I would love to believe
>> >> OPTEE will be the end-all TEE, I'm sure we soon will start to see wider
>> >> use of vendor TEEs (like TI's own legacy Trustzone thing we are hoping
>> >> to depreciate with OPTEE moving forward), possibly Google's Trusty TEE,
>> >> and whatever Intel/AMD are cooking up for x86.
>> >
>> > I'd rather say that it's slightly GlobalPlatform specific, but a bit
>> > more flexible.
>> >
>> >>
>> >> As we all know when things are upstreamed we lose the ability to make
>> >> radical changes easily, especially to full subsystems. What happens when
>> >> this framework, built with only one existing TEE, built by the one
>> >> existing TEE's devs, is not as flexible as we need when other TEEs start
>> >> rolling out?
>> >
>> > Initially the TEE subsystem was much more flexible and was criticized
>> > for that.
>> >
>>
>> That's rather strange, I haven't been following this from the start so I
>> will just take your word that this is where the community wants this
>> subsystem to go.
>>
>> >>
>> >> Do we see this as a chicken and egg situation, or is there any harm
>> >> beyond the pains of supporting an out-of-tree driver for a while, to
>> >> wait until we have at least one other TEE to add to this subsystem
>> >> before merging?
>> >
>> > This proposal is the bare minimum to have something useful. On top of
>> > this there's more things we'd like to add, for example an in-kernel API
>> > for accessing the TEE and secure buffer handling. The way we're dealing
>> > with shared memory need to be improved to better support multiple guests
>> > communicating with one TEE.
>> >
>> > What we can do now with the subsystem now is somewhat limited by the
>> > fact that we're trying to upstream it and want to do that it in
>> > manageable increments.
>> >
>>
>> Fair enough.
>>
>> For now this series is being used in our production SDKs so it has at
>> least some basic testing from us, so for the whole series:
>>
>> Tested-by: Andrew F. Davis <afd@...com>
>
> Thanks, Andrew. A summary of all tags so far:
>
> When I sent out this patch set I missed including the previous
> tested-bys:
> Tested-by: Jerome Forissier <jerome.forissier@...aro.org> (HiKey)
> Tested-by: Volodymyr Babchuk <vlad.babchuk@...il.com>
>
> Then there's also the acked-by from Andreas which should have been
> included even if the mail now bounces:
> Acked-by: Andreas Dannenberg <dannenberg@...com>
>
> The DT patch has (since v8):
> Acked-by: Rob Herring <robh@...nel.org>
>
> Thanks,
> Jens


Jens,

I want to specify that I tested those patches on Renesas RCAR H3 platform.
So my please update my Tested-by:

Tested-by: Volodymyr Babchuk <vlad.babchuk@...il.com> (RCAR H3)

As far as I know, Renesas plans to use OP-TEE as a driver for cryptographic
accelerators and others secure peripherals. So TEE support will be crucial
for theirs platform.

Also I suspect that every platform on ARMv8 will include ARM Trusted Firmware
(because it now provides PSCI) and some sort of TEE. So we really need
generic TEE interface in the kernel.

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