[RFC 11/14] efi_loader: variable: export variables table for runtime access

[Sughosh Ganu]

On Tue, 17 Mar 2020 at 07:42, AKASHI Takahiro <takahiro.akashi at linaro.org>
wrote:

> There are platforms on which OS's won't be able to access UEFI variables
> at runtime (i.e. after ExitBootServices).
> With this patch, all the UEFI variables are exported as a configuration
> table so as to enable retrieving variables' values from the table, and
> later modifying them via capsule-on-disk if necessary.
>
> The idea is based on Peter's proposal[1] in boot-arch ML.
>
> [1]
> https://lists.linaro.org/pipermail/boot-architecture/2018-October/000883.html
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
> ---
>  include/efi_loader.h          |   7 +++
>  lib/efi_loader/Kconfig        |  10 ++++
>  lib/efi_loader/efi_boottime.c |  10 ++++
>  lib/efi_loader/efi_capsule.c  |   4 ++
>  lib/efi_loader/efi_variable.c | 109 ++++++++++++++++++++++++++++++++++
>  5 files changed, 140 insertions(+)
>
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index 79bdf9586d24..93ed5502821c 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -183,6 +183,8 @@ extern const efi_guid_t efi_guid_hii_string_protocol;
>  extern const efi_guid_t efi_guid_capsule_report;
>  /* GUID of firmware management protocol */
>  extern const efi_guid_t efi_guid_firmware_management_protocol;
> +/* GUID of runtime variable access */
> +extern const efi_guid_t efi_guid_variable_storage;
>
>  /* GUID of RNG protocol */
>  extern const efi_guid_t efi_guid_rng_protocol;
> @@ -659,6 +661,10 @@ efi_status_t EFIAPI efi_query_variable_info(
>                         u64 *remaining_variable_storage_size,
>                         u64 *maximum_variable_size);
>
> +#ifdef CONFIG_EFI_VARIABLE_EXPORT
> +efi_status_t efi_install_variables_table(void);
> +#endif
> +
>  /*
>   * See section 3.1.3 in the v2.7 UEFI spec for more details on
>   * the layout of EFI_LOAD_OPTION.  In short it is:
> @@ -683,6 +689,7 @@ struct efi_load_option {
>  void efi_deserialize_load_option(struct efi_load_option *lo, u8 *data);
>  unsigned long efi_serialize_load_option(struct efi_load_option *lo, u8
> **data);
>  efi_status_t efi_bootmgr_load(efi_handle_t *handle);
> +efi_status_t efi_install_variables_table(void);
>
>  /* Capsule update */
>  efi_status_t EFIAPI efi_update_capsule(
> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> index 616e2acbe102..edb8d19059ea 100644
> --- a/lib/efi_loader/Kconfig
> +++ b/lib/efi_loader/Kconfig
> @@ -41,6 +41,16 @@ config EFI_SET_TIME
>           Provide the SetTime() runtime service at boottime. This service
>           can be used by an EFI application to adjust the real time clock.
>
> +config EFI_VARIABLE_EXPORT
> +       bool "Export variables table as configuration table"
> +       depends on !EFI_VARIABLE_RUNTIME_ACCESS
> +       depends on  EFI_CAPSULE_UPDATE_VARIABLE
> +       default y
> +       help
> +         Select this option if you want to export UEFI variables as
> +         configuration table so that OS can still get UEFI variable's
> +         value.
> +
>  config EFI_DEVICE_PATH_TO_TEXT
>         bool "Device path to text protocol"
>         default y
> diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
> index c2a789b4f910..406644e4da67 100644
> --- a/lib/efi_loader/efi_boottime.c
> +++ b/lib/efi_loader/efi_boottime.c
> @@ -2898,6 +2898,16 @@ efi_status_t EFIAPI efi_start_image(efi_handle_t
> image_handle,
>         if (ret != EFI_SUCCESS)
>                 return EFI_EXIT(EFI_INVALID_PARAMETER);
>
> +#ifdef CONFIG_EFI_VARIABLE_EXPORT
> +       /* Install variables database as a configuration table */
> +       ret = efi_install_variables_table();
> +       if (ret != EFI_SUCCESS)
> +               return EFI_EXIT(ret);
> +#endif
> +       /*
> +        * TODO: remove a table after image is terminated.
> +        */
> +
>         image_obj->exit_data_size = exit_data_size;
>         image_obj->exit_data = exit_data;
>
> diff --git a/lib/efi_loader/efi_capsule.c b/lib/efi_loader/efi_capsule.c
> index 1293270aea95..6b737aec1b28 100644
> --- a/lib/efi_loader/efi_capsule.c
> +++ b/lib/efi_loader/efi_capsule.c
> @@ -18,7 +18,11 @@ static const efi_guid_t
> efi_guid_firmware_management_capsule_id =
>                 EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID;
>  const efi_guid_t efi_guid_firmware_management_protocol =
>                 EFI_FIRMWARE_MANAGEMENT_PROTOCOL_GUID;
> +#ifdef CONFIG_EFI_VARIABLE_EXPORT
> +const efi_guid_t efi_guid_variable_storage = EFI_VARIABLE_STORAGE_GUID;
> +#else
>  static const efi_guid_t efi_guid_variable_storage =
> EFI_VARIABLE_STORAGE_GUID;
> +#endif
>

Need to remove the static keyword here. The build fails when
CONFIG_EFI_VARIABLE_EXPORT is not defined, with the extern declaration now
being done in efi_loader.h

-sughosh