Re: [PATCH v12 09/10] arm_ffa: efi: introduce FF-A MM communication

Ilias Apalodimas
2023-05-19T12:56:13Z

Hi Abdellatif

I still have some concerns on this

In the past [0] I asking why this needs to be a Kconfig option. Since FF-A
is a mechanism we can use to discover SPs, in theory we dont need the
ifdefery. We might need something if the code difference grows too much
but I think we are fine for now.

On top of that I am nissing how was this tested? did you test the current
SMC to optee and the stmm for the RPMB backend?

> +++ b/include/mm_communication.h
> @@ -6,6 +6,9 @@
> * Copyright (c) 2017, Intel Corporation. All rights reserved.
> * Copyright (C) 2020 Linaro Ltd. <sughosh.ganu@linaro.org>
> * Copyright (C) 2020 Linaro Ltd. <ilias.apalodimas@linaro.org>
> + * Copyright 2022-2023 Arm Limited and/or its affiliates <open-source-office@arm.com>
> + * Authors:
> + * Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
> */
>
> #ifndef _MM_COMMUNICATION_H_
> @@ -13,6 +16,9 @@
>
> #include <part_efi.h>
>
> +/* MM service UUID string (big-endian format). This UUID is common across all MM SPs */
> +#define MM_SP_UUID "33d532ed-e699-0942-c09c-a798d9cd722d"
> +
> /*
> * Interface to the pseudo Trusted Application (TA), which provides a
> * communication channel with the Standalone MM (Management Mode)
> @@ -248,4 +254,11 @@ struct smm_variable_var_check_property {
> u16 name[];
> };
>
> +/* supported MM transports */
> +enum mm_comms_select {
> + MM_COMMS_UNDEFINED,
> + MM_COMMS_FFA,
> + MM_COMMS_OPTEE
> +};
> +
> #endif /* _MM_COMMUNICATION_H_ */
> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> index c5835e6ef6..08a6b84101 100644
> --- a/lib/efi_loader/Kconfig
> +++ b/lib/efi_loader/Kconfig
> @@ -55,13 +55,23 @@ config EFI_VARIABLE_FILE_STORE
> stored as file /ubootefi.var on the EFI system partition.
>
> config EFI_MM_COMM_TEE
> - bool "UEFI variables storage service via OP-TEE"
> - depends on OPTEE
> + bool "UEFI variables storage service via the trusted world"
> + depends on OPTEE || ARM_FFA_TRANSPORT
> help
> + Allowing access to the MM SP services (SPs such as StandAlonneMM, smm-gateway).
> + When using the u-boot OP-TEE driver, StandAlonneMM is supported.
> + When using the u-boot FF-A driver any MM SP is supported.
> +
> If OP-TEE is present and running StandAloneMM, dispatch all UEFI
> variable related operations to that. The application will verify,
> authenticate and store the variables on an RPMB.
>
> + When ARM_FFA_TRANSPORT is used, dispatch all UEFI variable related
> + operations to the MM SP running in the secure world.
> + A door bell mechanism is used to notify the SP when there is data in the shared
> + MM buffer. The data is copied by u-boot to the shared buffer before issuing
> + the door bell event.
> +
> config EFI_VARIABLE_NO_STORE
> bool "Don't persist non-volatile UEFI variables"
> help
> diff --git a/lib/efi_loader/efi_variable_tee.c b/lib/efi_loader/efi_variable_tee.c
> index dfef18435d..2effb705d7 100644
> --- a/lib/efi_loader/efi_variable_tee.c
> +++ b/lib/efi_loader/efi_variable_tee.c
> @@ -4,9 +4,14 @@
> *
> * Copyright (C) 2019 Linaro Ltd. <sughosh.ganu@linaro.org>
> * Copyright (C) 2019 Linaro Ltd. <ilias.apalodimas@linaro.org>
> + * Copyright 2022-2023 Arm Limited and/or its affiliates <open-source-office@arm.com>
> + *
> + * Authors:
> + * Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
> */
>
> #include <common.h>
> +#include <dm.h>
> #include <efi.h>
> #include <efi_api.h>
> #include <efi_loader.h>
> @@ -15,6 +20,36 @@
> #include <malloc.h>
> #include <mm_communication.h>
>
> +#if IS_ENABLED(CONFIG_ARM_FFA_TRANSPORT)
> +
> +#include <arm_ffa.h>
> +#include <cpu_func.h>
> +#include <mapmem.h>
> +
> +#ifndef FFA_SHARED_MM_BUFFER_SIZE
> +#error "FFA_SHARED_MM_BUFFER_SIZE must be defined in include/configs/<board>.h"
> +#define FFA_SHARED_MM_BUFFER_SIZE 0
> +#endif
> +
> +#ifndef FFA_SHARED_MM_BUFFER_OFFSET
> +#error "FFA_SHARED_MM_BUFFER_OFFSET must be defined in include/configs/<board>.h"
> +#define FFA_SHARED_MM_BUFFER_OFFSET 0
> +#endif
> +
> +#ifndef FFA_SHARED_MM_BUFFER_ADDR
> +#error "FFA_SHARED_MM_BUFFER_ADDR must be defined in include/configs/<board>.h"
> +#define FFA_SHARED_MM_BUFFER_ADDR 0
> +#endif
> +
> +/* MM return codes */
> +#define MM_SUCCESS (0)
> +
> +static const char *mm_sp_svc_uuid = MM_SP_UUID;
> +
> +static u16 mm_sp_id;
> +
> +#endif
> +
> extern struct efi_var_file __efi_runtime_data *efi_var_buf;
> static efi_uintn_t max_buffer_size; /* comm + var + func + data */
> static efi_uintn_t max_payload_size; /* func + data */
> @@ -24,6 +59,7 @@ struct mm_connection {
> u32 session;
> };
>
> +#if (IS_ENABLED(CONFIG_OPTEE))

> /**
> * get_connection() - Retrieve OP-TEE session for a specific UUID.
> *

[...]

Isn't this problematic? At the moment there's not > 8.4 hardware out
there. As a result the SPMC *is* implemented in OP-TEE. So how do we
expect FF-A to work?

[...]

[0] https://lore.kernel.org/u-boot/Y3NV991bKRgas1zZ@hera/

Thanks
/Ilias