[PATCH v3 2/3] efi_firmware: set EFI capsule dfu_alt_info env explicitly

[Ilias Apalodimas]

Hi Jonathan, 

The patch looks correct but there's a few more things to address.

On Thu, Feb 13, 2025 at 01:53:50PM -0600, Jonathan Humphreys wrote:
> The current implementation of EFI capsule update uses set_dfu_alt_info() to
> set the dfu_alt_info environment variable with the settings it requires.
> However, set_dfu_alt_info() is doing this for all DFU operations, even
> those unrelated to capsule update.
> 
> Thus other uses of DFU, such as DFU boot which sets its own value for the
> dfu_alt_info environment variable, will have that setting overwritten with
> the capsule update setting. Similarly, any user defined value for the
> dfu_alt_info environment variable would get overwritten when any DFU
> operation was performed, including simply performing a "dfu 0 list"
> command.
> 
> The solution is stop using the set_dfu_alt_info() mechanism to set the
> dfu_alt_info environment variable and instead explicitly set it to the
> capsule update's setting just before performing the capsule update's DFU
> operation, and then restore the environment variable back to its original
> value.
> 
> This patch implements the explicit setting and restoring of the
> dfu_alt_info environment variable as part of the EFI capsule update
> operation.
> 
> The fix is fully implemented in a subsequent patch that removes the capsule
> update dfu_alt_info support in set_dfu_alt_info().
> 
> Signed-off-by: Jonathan Humphreys <j-humphreys at ti.com>
> ---
>  lib/efi_loader/efi_firmware.c | 39 ++++++++++++++++++++++++++++++++---
>  1 file changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/efi_loader/efi_firmware.c b/lib/efi_loader/efi_firmware.c
> index 5a754c9cd03..1a1cf3b55e1 100644
> --- a/lib/efi_loader/efi_firmware.c
> +++ b/lib/efi_loader/efi_firmware.c
> @@ -649,8 +649,10 @@ efi_status_t EFIAPI efi_firmware_fit_set_image(
>  	efi_status_t (*progress)(efi_uintn_t completion),
>  	u16 **abort_reason)
>  {
> +	int ret;
>  	efi_status_t status;
>  	struct fmp_state state = { 0 };
> +	char *orig_dfu_env;
>  
>  	EFI_ENTRY("%p %d %p %zu %p %p %p\n", this, image_index, image,
>  		  image_size, vendor_code, progress, abort_reason);
> @@ -663,7 +665,22 @@ efi_status_t EFIAPI efi_firmware_fit_set_image(
>  	if (status != EFI_SUCCESS)
>  		return EFI_EXIT(status);
>  
> -	if (fit_update(image))
> +	orig_dfu_env = strdup(env_get("dfu_alt_info"));

strdup might fail, we need to check that the orig_dfu_env is !NULL

> +	if (env_set("dfu_alt_info", update_info.dfu_string)) {
> +		log_err("unable to set env variable \"dfu_alt_info\"!\n");
> +		free(orig_dfu_env);
> +		return EFI_EXIT(EFI_DEVICE_ERROR);
> +	}
> +
> +	ret = fit_update(image);

> +
> +	if (env_set("dfu_alt_info", orig_dfu_env)) {
> +		log_err("unable to set env variable \"dfu_alt_info\"!\n");
> +		ret = 1;

This will work but for consistency just use an EFI defined error e.g 
ret = EFI_DEVICE_ERROR;

> +	}
> +	free(orig_dfu_env);
> +
> +	if (ret)

I am not 100% sure this exiting here is useful. If fit_update has succeeded
we have updated our firmware. So I think we should just add a warning here,
that resetting the dfu to its original value failed, and any further dfu
ops will fail. 

>  		return EFI_EXIT(EFI_DEVICE_ERROR);
>  
>  	efi_firmware_set_fmp_state_var(&state, image_index);
> @@ -717,6 +734,7 @@ efi_status_t EFIAPI efi_firmware_raw_set_image(
>  	u8 dfu_alt_num;
>  	efi_status_t status;
>  	struct fmp_state state = { 0 };
> +	char *orig_dfu_env;
>  
>  	EFI_ENTRY("%p %d %p %zu %p %p %p\n", this, image_index, image,
>  		  image_size, vendor_code, progress, abort_reason);
> @@ -747,8 +765,23 @@ efi_status_t EFIAPI efi_firmware_raw_set_image(
>  		}
>  	}
>  
> -	if (dfu_write_by_alt(dfu_alt_num, (void *)image, image_size,
> -			     NULL, NULL))
> +	orig_dfu_env = strdup(env_get("dfu_alt_info"));
> +	if (env_set("dfu_alt_info", update_info.dfu_string)) {
> +		log_err("unable to set env variable \"dfu_alt_info\"!\n");
> +		free(orig_dfu_env);
> +		return EFI_EXIT(EFI_DEVICE_ERROR);
> +	}
> +
> +	ret = dfu_write_by_alt(dfu_alt_num, (void *)image, image_size,
> +			       NULL, NULL);
> +
> +	if (env_set("dfu_alt_info", orig_dfu_env)) {
> +		log_err("unable to set env variable \"dfu_alt_info\"!\n");
> +		ret = 1;
> +	}
> +	free(orig_dfu_env);
> +
> +	if (ret)
>  		return EFI_EXIT(EFI_DEVICE_ERROR);
>  
>  	efi_firmware_set_fmp_state_var(&state, image_index);
> -- 
> 2.34.1
> 

Thanks
/Ilias