Message-ID: <20161029094641.GA23362@ermac>
Date:   Sat, 29 Oct 2016 11:46:42 +0200
From:   Jens Wiklander <jens.wiklander@...aro.org>
To:     "Andrew F. Davis" <afd@...com>
Cc:     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, vlad.babchuk@...il.com
Subject: Re: [PATCH v12 RESEND 0/4] generic TEE subsystem

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.

> 
> 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.

Thanks,
Jens

> 
> This may also help with the perceived lack of reviewers for this series.
> 
> Thanks,
> Andrew
> 
> > "tee: generic TEE subsystem" brings in the generic TEE subsystem which
> > helps when writing a driver for a specific TEE, for example, OP-TEE.
> > 
> > "tee: add OP-TEE driver" is an OP-TEE driver which uses the subsystem to do
> > its work.
> > 
> > This patch set has been prepared in cooperation with Javier González who
> > proposed "Generic TrustZone Driver in Linux Kernel" patches 28 Nov 2014,
> > https://lwn.net/Articles/623380/ . We've since then changed the scope to
> > TEE instead of TrustZone.
> > 
> > We have discussed the design on tee-dev@...ts.linaro.org (archive at
> > https://lists.linaro.org/pipermail/tee-dev/) with people from other
> > companies, including Valentin Manea <valentin.manea@...wei.com>,
> > Emmanuel MICHEL <emmanuel.michel@...com>,
> > Jean-michel DELORME <jean-michel.delorme@...com>,
> > and Joakim Bech <joakim.bech@...aro.org>. Our main concern has been to
> > agree on something that is generic enough to support many different
> > TEEs while still keeping the interface together.
> > 
> > v12-resend:
> > * Rebased on v4.9-rc2
> > 
> > v12:
> > * Rebased on v4.8-rc5
> > * Addressed review comments from Andrew F. Davis
> > * Removed Acked-by: Andreas Dannenberg <dannenberg@...com> as the
> >   mail bounces
> > * Bugfix possible null dereference in error cleanup path of
> >   optee_probe().
> > * Bugfix optee_from_msg_param() when calculating offset of memref
> >   into a shared memory object
> > 
> > v11:
> > * Rebased on v4.8-rc3
> > * Addressed review comments from Nishanth Menon
> > * Made the TEE framework available as a loadable module.
> > * Reviewed-by: Javier González <javier@...igon.com>
> > * Zeroes shared memory on allocation to avoid information leakage
> > * Links shared memory objects to context to avoid stealing of shared memory
> >   object from an unrelated process
> > * Allow RPC interruption if supplicant is unavailable
> > 
> > v10:
> > * Rebased on v4.7-rc1
> > * Addressed private review comments from Nishanth Menon
> > * Optee driver only accepts one supplicant process on the privileged device
> > * Optee driver avoids long delayed releases of shm objects
> > * Added more comments on functions and structs
> > 
> > v9:
> > * Rebased on v4.6-rc1
> > * Acked-by: Andreas Dannenberg <dannenberg@...com>
> > * Addressed comments from Al Viro how file descriptors are passed to
> >   user space
> > * Addressed comments from Randy Dunlap on documentation
> > * Changed license for include/uapi/linux/tee.h
> > 
> > v8:
> > * Rebased on v4.5-rc3
> > * dt/bindings: add bindings for optee
> >   Acked-by: Rob Herring <robh@...nel.org>
> > * Fixes build error for X86
> > * Fixes spell error in "dt/bindings: add bindings for optee"
> > 
> > v7:
> > * Rebased on v4.5-rc2
> > * Moved the ARM SMC Calling Convention support into a separate patch
> >   set, which is now merged
> > 
> > v6:
> > * Rebased on v4.3-rc7
> > * Changed smccc interface to let the compiler marshal most of the
> >   parameters
> > * Added ARCH64 capability for smccc interface
> > * Changed the PSCI firmware calls (both arm and arm64) to use the new
> >   generic smccc interface instead instead of own assembly functions.
> > * Move optee DT bindings to below arm/firmware
> > * Defines method for OP-TEE driver to call secure world in DT, smc or hvc
> > * Exposes implementation id of a TEE driver in sysfs
> >   to easily spawn corresponding tee-supplicant when device is ready
> > * Update OP-TEE Message Protocol to better cope with fragmented physical
> >   memory
> > * Read time directly from OP-TEE driver instead of forwarding the RPC
> >   request to tee-supplicant
> > 
> > v5:
> > * Replaced kref reference counting for the device with a size_t instead as
> >   the counter is always protected by a mutex
> > 
> > v4:
> > * Rebased on 4.1
> > * Redesigned the synchronization around entry exit of normal SMC
> > * Replaced rwsem on the driver instance with kref and completion since
> >   rwsem wasn't intended to be used in this way
> > * Expanded the TEE_IOCTL_PARAM_ATTR_TYPE_MASK to make room for
> >   future additional parameter types
> > * Documents TEE subsystem and OP-TEE driver
> > * Replaced TEE_IOC_CMD with TEE_IOC_OPEN_SESSION, TEE_IOC_INVOKE,
> >   TEE_IOC_CANCEL and TEE_IOC_CLOSE_SESSION
> > * DT bindings in a separate patch
> > * Assembly parts moved to arch/arm and arch/arm64 respectively, in a
> >   separate patch
> > * Redefined/clarified the meaning of OPTEE_SMC_SHM_CACHED
> > * Removed CMA usage to limit the scope of the patch set
> > 
> > v3:
> > * Rebased on 4.1-rc3 (dma_buf_export() API change)
> > * A couple of small sparse fixes
> > * Documents bindings for OP-TEE driver
> > * Updated MAINTAINERS
> > 
> > v2:
> > * Replaced the stubbed OP-TEE driver with a real OP-TEE driver
> > * Removed most APIs not needed by OP-TEE in current state
> > * Update Documentation/ioctl/ioctl-number.txt with correct path to tee.h
> > * Rename tee_shm_pool_alloc_cma() to tee_shm_pool_alloc()
> > * Moved tee.h into include/uapi/linux/
> > * Redefined tee.h IOCTL macros to be directly based on _IOR and friends
> > * Removed version info on the API to user space, a data blob which
> >   can contain an UUID is left for user space to be able to tell which
> >   protocol to use in TEE_IOC_CMD
> > * Changed user space exposed structures to only have types with __ prefix
> > * Dropped THIS_MODULE from tee_fops
> > * Reworked how the driver is registered and ref counted:
> >   - moved from using an embedded struct miscdevice to an embedded struct
> >     device.
> >   - uses an struct rw_semaphore as synchronization for driver detachment
> >   - uses alloc/register pattern from TPM
> > 
> > Thanks,
> > Jens
> > 
> > Jens Wiklander (4):
> >   dt/bindings: add bindings for optee
> >   tee: generic TEE subsystem
> >   tee: add OP-TEE driver
> >   Documentation: tee subsystem and op-tee driver
> > 
> >  Documentation/00-INDEX                             |   2 +
> >  .../bindings/arm/firmware/linaro,optee-tz.txt      |  31 +
> >  .../devicetree/bindings/vendor-prefixes.txt        |   1 +
> >  Documentation/ioctl/ioctl-number.txt               |   1 +
> >  Documentation/tee.txt                              | 118 +++
> >  MAINTAINERS                                        |  13 +
> >  drivers/Kconfig                                    |   2 +
> >  drivers/Makefile                                   |   1 +
> >  drivers/tee/Kconfig                                |  18 +
> >  drivers/tee/Makefile                               |   5 +
> >  drivers/tee/optee/Kconfig                          |   7 +
> >  drivers/tee/optee/Makefile                         |   5 +
> >  drivers/tee/optee/call.c                           | 435 ++++++++++
> >  drivers/tee/optee/core.c                           | 598 ++++++++++++++
> >  drivers/tee/optee/optee_msg.h                      | 435 ++++++++++
> >  drivers/tee/optee/optee_private.h                  | 185 +++++
> >  drivers/tee/optee/optee_smc.h                      | 446 ++++++++++
> >  drivers/tee/optee/rpc.c                            | 404 +++++++++
> >  drivers/tee/optee/supp.c                           | 273 +++++++
> >  drivers/tee/tee_core.c                             | 901 +++++++++++++++++++++
> >  drivers/tee/tee_private.h                          | 129 +++
> >  drivers/tee/tee_shm.c                              | 357 ++++++++
> >  drivers/tee/tee_shm_pool.c                         | 158 ++++
> >  include/linux/tee_drv.h                            | 278 +++++++
> >  include/uapi/linux/tee.h                           | 403 +++++++++
> >  25 files changed, 5206 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/arm/firmware/linaro,optee-tz.txt
> >  create mode 100644 Documentation/tee.txt
> >  create mode 100644 drivers/tee/Kconfig
> >  create mode 100644 drivers/tee/Makefile
> >  create mode 100644 drivers/tee/optee/Kconfig
> >  create mode 100644 drivers/tee/optee/Makefile
> >  create mode 100644 drivers/tee/optee/call.c
> >  create mode 100644 drivers/tee/optee/core.c
> >  create mode 100644 drivers/tee/optee/optee_msg.h
> >  create mode 100644 drivers/tee/optee/optee_private.h
> >  create mode 100644 drivers/tee/optee/optee_smc.h
> >  create mode 100644 drivers/tee/optee/rpc.c
> >  create mode 100644 drivers/tee/optee/supp.c
> >  create mode 100644 drivers/tee/tee_core.c
> >  create mode 100644 drivers/tee/tee_private.h
> >  create mode 100644 drivers/tee/tee_shm.c
> >  create mode 100644 drivers/tee/tee_shm_pool.c
> >  create mode 100644 include/linux/tee_drv.h
> >  create mode 100644 include/uapi/linux/tee.h
> > 

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