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

Sughosh Ganu
2020-03-18T13:54:20Z

On Tue, 17 Mar 2020 at 07:42, AKASHI Takahiro <takahiro.akashi@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@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