Re: [PATCH 4/4] Documentation: tee: add AMD-TEE driver details

[Gary R Hook]

On 12/26/19 11:24 PM, Rijo Thomas wrote:
> Update tee.txt with AMD-TEE driver details. The driver is written
> to communicate with AMD's TEE.
>
> Acked-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> Co-developed-by: Devaraj Rangasamy <Devaraj.Rangasamy@xxxxxxx>
> Signed-off-by: Devaraj Rangasamy <Devaraj.Rangasamy@xxxxxxx>
> Signed-off-by: Rijo Thomas <Rijo-john.Thomas@xxxxxxx>

Reviewed-by: Gary R Hook <gary.hook@xxxxxxx>

> ---
>   Documentation/tee.txt | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 81 insertions(+)
>
> diff --git a/Documentation/tee.txt b/Documentation/tee.txt
> index afacdf2..c8fad81 100644
> --- a/Documentation/tee.txt
> +++ b/Documentation/tee.txt
> @@ -112,6 +112,83 @@ kernel are handled by the kernel driver. Other RPC messages will be forwarded to
>   tee-supplicant without further involvement of the driver, except switching
>   shared memory buffer representation.
>   
> +AMD-TEE driver
> +==============
> +
> +The AMD-TEE driver handles the communication with AMD's TEE environment. The
> +TEE environment is provided by AMD Secure Processor.
> +
> +The AMD Secure Processor (formerly called Platform Security Processor or PSP)
> +is a dedicated processor that features ARM TrustZone technology, along with a
> +software-based Trusted Execution Environment (TEE) designed to enable
> +third-party Trusted Applications. This feature is currently enabled only for
> +APUs.
> +
> +The following picture shows a high level overview of AMD-TEE::
> +
> +                                             |
> +    x86                                      |
> +                                             |
> + User space            (Kernel space)        |    AMD Secure Processor (PSP)
> + ~~~~~~~~~~            ~~~~~~~~~~~~~~        |    ~~~~~~~~~~~~~~~~~~~~~~~~~~
> +                                             |
> + +--------+                                  |       +-------------+
> + | Client |                                  |       | Trusted     |
> + +--------+                                  |       | Application |
> +     /\                                      |       +-------------+
> +     ||                                      |             /\
> +     ||                                      |             ||
> +     ||                                      |             \/
> +     ||                                      |         +----------+
> +     ||                                      |         |   TEE    |
> +     ||                                      |         | Internal |
> +     \/                                      |         |   API    |
> + +---------+           +-----------+---------+         +----------+
> + | TEE     |           | TEE       | AMD-TEE |         | AMD-TEE  |
> + | Client  |           | subsystem | driver  |         | Trusted  |
> + | API     |           |           |         |         |   OS     |
> + +---------+-----------+----+------+---------+---------+----------+
> + |   Generic TEE API        |      | ASP     |      Mailbox       |
> + |   IOCTL (TEE_IOC_*)      |      | driver  | Register Protocol  |
> + +--------------------------+      +---------+--------------------+
> +
> +At the lowest level (in x86), the AMD Secure Processor (ASP) driver uses the
> +CPU to PSP mailbox regsister to submit commands to the PSP. The format of the
> +command buffer is opaque to the ASP driver. It's role is to submit commands to
> +the secure processor and return results to AMD-TEE driver. The interface
> +between AMD-TEE driver and AMD Secure Processor driver can be found in [6].
> +
> +The AMD-TEE driver packages the command buffer payload for processing in TEE.
> +The command buffer format for the different TEE commands can be found in [7].
> +
> +The TEE commands supported by AMD-TEE Trusted OS are:
> +* TEE_CMD_ID_LOAD_TA          - loads a Trusted Application (TA) binary into
> +                                TEE environment.
> +* TEE_CMD_ID_UNLOAD_TA        - unloads TA binary from TEE environment.
> +* TEE_CMD_ID_OPEN_SESSION     - opens a session with a loaded TA.
> +* TEE_CMD_ID_CLOSE_SESSION    - closes session with loaded TA
> +* TEE_CMD_ID_INVOKE_CMD       - invokes a command with loaded TA
> +* TEE_CMD_ID_MAP_SHARED_MEM   - maps shared memory
> +* TEE_CMD_ID_UNMAP_SHARED_MEM - unmaps shared memory
> +
> +AMD-TEE Trusted OS is the firmware running on AMD Secure Processor.
> +
> +The AMD-TEE driver registers itself with TEE subsystem and implements the
> +following driver function callbacks:
> +
> +* get_version - returns the driver implementation id and capability.
> +* open - sets up the driver context data structure.
> +* release - frees up driver resources.
> +* open_session - loads the TA binary and opens session with loaded TA.
> +* close_session -  closes session with loaded TA and unloads it.
> +* invoke_func - invokes a command with loaded TA.
> +
> +cancel_req driver callback is not supported by AMD-TEE.
> +
> +The GlobalPlatform TEE Client API [5] can be used by the user space (client) to
> +talk to AMD's TEE. AMD's TEE provides a secure environment for loading, opening
> +a session, invoking commands and clossing session with TA.
> +
>   References
>   ==========
>   
> @@ -125,3 +202,7 @@ References
>   
>   [5] http://www.globalplatform.org/specificationsdevice.asp look for
>       "TEE Client API Specification v1.0" and click download.
> +
> +[6] include/linux/psp-tee.h
> +
> +[7] drivers/tee/amdtee/amdtee_if.h