linux-kernel - Re: [PATCH v4 0/3] introduce tee-based EFI Runtime Variable Service

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Message-ID: <CAFA6WYOOEwd=jWk1LEaj9K2GkjfV+kfPYOfwPkJVoWXJKGoQXA@mail.gmail.com>
Date:   Wed, 24 May 2023 13:26:18 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Masahisa Kojima <masahisa.kojima@...aro.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        linux-kernel@...r.kernel.org, op-tee@...ts.trustedfirmware.org,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v4 0/3] introduce tee-based EFI Runtime Variable Service

On Tue, 23 May 2023 at 14:36, Masahisa Kojima
<masahisa.kojima@...aro.org> wrote:
>
> This series introduces the tee based EFI Runtime Variable Service.
>
> The eMMC device is typically owned by the non-secure world(linux in
> this case). There is an existing solution utilizing eMMC RPMB partition
> for EFI Variables, it is implemented by interacting with
> OP-TEE, StandaloneMM(as EFI Variable Service Pseudo TA), eMMC driver
> and tee-supplicant. The last piece is the tee-based variable access
> driver to interact with OP-TEE and StandaloneMM.
>
> Changelog:
> v3 -> v4:
> - replace the reference from EDK2 to PI Specification
> - remove EDK2 source code reference comments
> - prepare nonblocking variant of set_variable, it just returns
>   EFI_UNSUPPORTED
> - remove redundant buffer size check
> - argument name change in mm_communicate
> - function interface changes in setup_mm_hdr to remove (void **) cast

I don't have detailed insights into how EFI spec mandates StandaloneMM
should be implemented. But utilizing OP-TEE as the underlying
transport here looks fine to me. FWIW,

For the series:
Acked-by: Sumit Garg <sumit.garg@...aro.org>

-Sumit

>
> v2 -> v3:
> - add CONFIG_EFI dependency to TEE_STMM_EFI
> - add missing return code check for tee_client_invoke_func()
> - directly call efivars_register/unregister from tee_stmm_efi.c
>
> rfc v1 -> v2:
> - split patch into three patches, one for drivers/tee,
>   one for include/linux/efi.h, and one for the driver/firmware/efi/stmm
> - context/session management into probe() and remove() same as other tee
> client driver
> - StMM variable driver is moved from driver/tee/optee to driver/firmware/efi
> - use "tee" prefix instead of "optee" in driver/firmware/efi/stmm/tee_stmm_efi.c,
>   this file does not contain op-tee specific code, abstracted by tee layer and
>   StMM variable driver will work on other tee implementation.
> - PTA_STMM_CMD_COMMUNICATE -> PTA_STMM_CMD_COMMUNICATE
> - implement query_variable_store() but currently not used
> - no use of TEEC_SUCCESS, it is defined in driver/tee/optee/optee_private.h.
>   Other tee client drivers use 0 instead of using TEEC_SUCCESS
> - remove TEEC_ERROR_EXCESS_DATA status, it is referred just to output
> error message
>
> Masahisa Kojima (3):
>   efi: expose efivar generic ops register function
>   efi: Add EFI_ACCESS_DENIED status code
>   efi: Add tee-based EFI variable driver
>
>  drivers/firmware/efi/Kconfig                 |  15 +
>  drivers/firmware/efi/Makefile                |   1 +
>  drivers/firmware/efi/efi.c                   |  12 +
>  drivers/firmware/efi/stmm/mm_communication.h | 236 +++++++
>  drivers/firmware/efi/stmm/tee_stmm_efi.c     | 637 +++++++++++++++++++
>  include/linux/efi.h                          |   4 +
>  6 files changed, 905 insertions(+)
>  create mode 100644 drivers/firmware/efi/stmm/mm_communication.h
>  create mode 100644 drivers/firmware/efi/stmm/tee_stmm_efi.c
>
> --
> 2.30.2
>