Re: [PATCH 2/2] efi_loader: use short-form DP for load options

[AKASHI Takahiro <takahiro.akashi@linaro.org>]

On Sat, Feb 26, 2022 at 12:56:51PM +0100, Heinrich Schuchardt wrote:
> The GUID of partitions is sufficient for identification and will stay
> constant in the lifetime of a boot option. The preceding path of the
> device-path may change due to changes in the enumeration of devices.
> Therefore it is preferable to use the short-form of device-paths in load
> options. Adjust the 'efidebug boot add' command accordingly.

Since a "long" device path is still valid, I think that a user should
be allowed to use a long device path especially if he or she wants to
limit an interface for loading any image.
Please add an option to efidebug to select a short or long path.

Furthermore, I would like to ask you to add a test, as you always
require me to do so, for loading from a short path.
Otherwise, the feature will never be exercised in CI loop.

-Takahiro Akashi


> Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
> ---
>  cmd/efidebug.c                   | 15 +++++++++++----
>  include/efi_loader.h             |  3 ++-
>  lib/efi_loader/efi_device_path.c | 21 +++++++++++++--------
>  3 files changed, 26 insertions(+), 13 deletions(-)
> 
> diff --git a/cmd/efidebug.c b/cmd/efidebug.c
> index 401d13cc4c..f62a4345fd 100644
> --- a/cmd/efidebug.c
> +++ b/cmd/efidebug.c
> @@ -747,7 +747,7 @@ struct efi_device_path *create_initrd_dp(const char *dev, const char *part,
>  					 const char *file)
> 
>  {
> -	struct efi_device_path *tmp_dp = NULL, *tmp_fp = NULL;
> +	struct efi_device_path *tmp_dp = NULL, *tmp_fp = NULL, *short_fp;
>  	struct efi_device_path *initrd_dp = NULL;
>  	efi_status_t ret;
>  	const struct efi_initrd_dp id_dp = {
> @@ -771,9 +771,12 @@ struct efi_device_path *create_initrd_dp(const char *dev, const char *part,
>  		printf("Cannot create device path for \"%s %s\"\n", part, file);
>  		goto out;
>  	}
> +	short_fp = efi_dp_shorten(tmp_fp);
> +	if (!short_fp)
> +		short_fp = tmp_fp;
> 
>  	initrd_dp = efi_dp_append((const struct efi_device_path *)&id_dp,
> -				  tmp_fp);
> +				  short_fp);
> 
>  out:
>  	efi_free_pool(tmp_dp);
> @@ -807,6 +810,7 @@ static int do_efi_boot_add(struct cmd_tbl *cmdtp, int flag,
>  	size_t label_len, label_len16;
>  	u16 *label;
>  	struct efi_device_path *device_path = NULL, *file_path = NULL;
> +	struct efi_device_path *fp_free = NULL;
>  	struct efi_device_path *final_fp = NULL;
>  	struct efi_device_path *initrd_dp = NULL;
>  	struct efi_load_option lo;
> @@ -849,13 +853,16 @@ static int do_efi_boot_add(struct cmd_tbl *cmdtp, int flag,
> 
>  			/* file path */
>  			ret = efi_dp_from_name(argv[3], argv[4], argv[5],
> -					       &device_path, &file_path);
> +					       &device_path, &fp_free);
>  			if (ret != EFI_SUCCESS) {
>  				printf("Cannot create device path for \"%s %s\"\n",
>  				       argv[3], argv[4]);
>  				r = CMD_RET_FAILURE;
>  				goto out;
>  			}
> +			file_path = efi_dp_shorten(fp_free);
> +			if (!file_path)
> +				file_path = fp_free;
>  			fp_size += efi_dp_size(file_path) +
>  				sizeof(struct efi_device_path);
>  			argc -= 5;
> @@ -927,7 +934,7 @@ out:
>  	efi_free_pool(final_fp);
>  	efi_free_pool(initrd_dp);
>  	efi_free_pool(device_path);
> -	efi_free_pool(file_path);
> +	efi_free_pool(fp_free);
>  	free(lo.label);
> 
>  	return r;
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index e390d323a9..c7d6b7c7f3 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -725,7 +725,8 @@ extern void *efi_bounce_buffer;
>  #define EFI_LOADER_BOUNCE_BUFFER_SIZE (64 * 1024 * 1024)
>  #endif
> 
> -
> +/* shorten device path */
> +struct efi_device_path *efi_dp_shorten(struct efi_device_path *dp);
>  struct efi_device_path *efi_dp_next(const struct efi_device_path *dp);
>  int efi_dp_match(const struct efi_device_path *a,
>  		 const struct efi_device_path *b);
> diff --git a/lib/efi_loader/efi_device_path.c b/lib/efi_loader/efi_device_path.c
> index dc787b4d3d..ddd5f132ec 100644
> --- a/lib/efi_loader/efi_device_path.c
> +++ b/lib/efi_loader/efi_device_path.c
> @@ -122,20 +122,25 @@ int efi_dp_match(const struct efi_device_path *a,
>  	}
>  }
> 
> -/*
> +/**
> + * efi_dp_shorten() - shorten device-path
> + *
>   * We can have device paths that start with a USB WWID or a USB Class node,
>   * and a few other cases which don't encode the full device path with bus
>   * hierarchy:
>   *
> - *   - MESSAGING:USB_WWID
> - *   - MESSAGING:USB_CLASS
> - *   - MEDIA:FILE_PATH
> - *   - MEDIA:HARD_DRIVE
> - *   - MESSAGING:URI
> + * * MESSAGING:USB_WWID
> + * * MESSAGING:USB_CLASS
> + * * MEDIA:FILE_PATH
> + * * MEDIA:HARD_DRIVE
> + * * MESSAGING:URI
>   *
>   * See UEFI spec (section 3.1.2, about short-form device-paths)
> + *
> + * @dp:		original devie-path
> + * @Return:	shortened device-path or NULL
>   */
> -static struct efi_device_path *shorten_path(struct efi_device_path *dp)
> +struct efi_device_path *efi_dp_shorten(struct efi_device_path *dp)
>  {
>  	while (dp) {
>  		/*
> @@ -189,7 +194,7 @@ static struct efi_object *find_obj(struct efi_device_path *dp, bool short_path,
>  				}
>  			}
> 
> -			obj_dp = shorten_path(efi_dp_next(obj_dp));
> +			obj_dp = efi_dp_shorten(efi_dp_next(obj_dp));
>  		} while (short_path && obj_dp);
>  	}
> 
> --
> 2.34.1
>