[PATCH v4 3/5] efi_loader: check lowest supported version in capsule update

[Ilias Apalodimas]

On Thu, 23 Mar 2023 at 13:09, Masahisa Kojima
<masahisa.kojima at linaro.org> wrote:
>
> The FMP Payload Header which EDK II capsule generation scripts
> insert contains lowest supported version.
> This commit reads the lowest supported version stored in the
> "FmpStateXXXX" EFI non-volatile variable, then check if the
> firmware version of ongoing capsule is equal or greater than
> the lowest supported version.
>
> Signed-off-by: Masahisa Kojima <masahisa.kojima at linaro.org>
> ---
> Changes in v4:
> - use log_err() instead of printf()
>
> Changes in v2:
> - add error message when the firmware version is lower than
>   lowest supported version
>
>  lib/efi_loader/efi_firmware.c | 50 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/lib/efi_loader/efi_firmware.c b/lib/efi_loader/efi_firmware.c
> index 7536fcfa55..9c25b5bb38 100644
> --- a/lib/efi_loader/efi_firmware.c
> +++ b/lib/efi_loader/efi_firmware.c
> @@ -385,6 +385,39 @@ void efi_firmware_parse_payload_header(const void **p_image,
>         *p_image_size = image_size;
>  }
>
> +/**
> + * efi_firmware_get_lowest_supported_version - get the lowest supported version
> + * @image_index:       image_index
> + *
> + * Get the lowest supported version from FmpStateXXXX variable.
> + *
> + * Return:             lowest supported version, return 0 if reading FmpStateXXXX
> + *                     variable failed
> + */
> +static
> +u32 efi_firmware_get_lowest_supported_version(u8 image_index)
> +{
> +       u16 varname[13]; /* u"FmpStateXXXX" */
> +       efi_status_t ret;
> +       efi_uintn_t size;
> +       efi_guid_t *image_type_id;
> +       struct fmp_state var_state = { 0 };
> +
> +       image_type_id = efi_firmware_get_image_type_id(image_index);
> +       if (!image_type_id)
> +               return 0;
> +
> +       efi_create_indexed_name(varname, sizeof(varname), "FmpState",
> +                               image_index);
> +       size = sizeof(var_state);
> +       ret = efi_get_variable_int(varname, image_type_id, NULL, &size,
> +                                  &var_state, NULL);
> +       if (ret != EFI_SUCCESS)
> +               return 0;
> +
> +       return var_state.lowest_supported_version;
> +}
> +
>  /**
>   * efi_firmware_verify_image - verify image
>   * @p_image:           Pointer to new image
> @@ -392,7 +425,8 @@ void efi_firmware_parse_payload_header(const void **p_image,
>   * @image_index                Image index
>   * @state              Pointer to fmp state
>   *
> - * Verify the capsule file
> + * Verify the capsule authentication and check if the fw_version
> + * is equal or greater than the lowest supported version.
>   *
>   * Return:             status code
>   */
> @@ -403,10 +437,24 @@ efi_status_t efi_firmware_verify_image(const void **p_image,
>                                        struct fmp_state *state)
>  {
>         efi_status_t ret;
> +       u32 lowest_supported_version;
>
>         ret = efi_firmware_capsule_authenticate(p_image, p_image_size, state);
>         efi_firmware_parse_payload_header(p_image, p_image_size, state);
>
> +       /* check lowest_supported_version if capsule authentication passes */
> +       if (ret == EFI_SUCCESS) {
> +               lowest_supported_version =
> +                       efi_firmware_get_lowest_supported_version(image_index);
> +               if (lowest_supported_version > state->fw_version) {
> +                       log_err("Firmware version %u too low. Expecting >= %u. Aborting update\n",
> +                               state->fw_version, lowest_supported_version);
> +                       state->last_attempt_status =
> +                               LAST_ATTEMPT_STATUS_ERROR_INCORRECT_VERSION;
> +                       ret = EFI_INVALID_PARAMETER;
> +               }
> +       }
> +
>         return ret;
>  }
>
> --
> 2.17.1
>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>