[PATCH] efi: Restrict the simple file system protocol to support only FAT

[Masami Hiramatsu]

+Cc: Grant and Vincent

This will fix some EBBR certification test errors if the target
machine has any partition which is partially (e.g. read only)
supported by U-Boot. UEFI spec doesn't require accessing such
filesystems, but U-Boot provides.

Of course, we can also drop filesystem configs except for FAT
filesystem support for UEFI only platforms. But it doesn't help hybrid
platforms.

Thank you,

2021年6月3日(木) 11:17 Masami Hiramatsu <masami.hiramatsu at linaro.org>:
>
> Because UEFI specification v2.9, 13.3 File System Format said "The
> file system supported by the Extensible Firmware Interface is based
> on the FAT file system.", the simple file system protocol might be
> better to support only FAT filesystem.
>
> There must be no problem from UEFI application to access only FAT
> because ESP must be formatted by FAT32 and the removable media is
> FAT12 or FAT16, according to the UEFI spec.
>
> Reported-by: Kazuhiko Sakamoto <sakamoto.kazuhiko at socionext.com>
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu at linaro.org>
> ---
>  lib/efi_loader/efi_disk.c |   18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/lib/efi_loader/efi_disk.c b/lib/efi_loader/efi_disk.c
> index 307d5d759b..f69ae6587f 100644
> --- a/lib/efi_loader/efi_disk.c
> +++ b/lib/efi_loader/efi_disk.c
> @@ -318,19 +318,25 @@ efi_fs_from_path(struct efi_device_path *full_path)
>  }
>
>  /**
> - * efi_fs_exists() - check if a partition bears a file system
> + * efi_supported_fs_exists() - check if a partition bears a supported file system
>   *
>   * @desc:      block device descriptor
>   * @part:      partition number
> - * Return:     1 if a file system exists on the partition
> + * Return:     1 if a supported file system exists on the partition
>   *             0 otherwise
>   */
> -static int efi_fs_exists(struct blk_desc *desc, int part)
> +static int efi_supported_fs_exists(struct blk_desc *desc, int part)
>  {
>         if (fs_set_blk_dev_with_part(desc, part))
>                 return 0;
>
> -       if (fs_get_type() == FS_TYPE_ANY)
> +       /*
> +        * Because UEFI specification v2.9, 13.3 File System Format said
> +        * "The file system supported by the Extensible Firmware Interface
> +        * is based on the FAT file system.", the simple file system protocol
> +        * should support only FAT filesystem.
> +        */
> +       if (fs_get_type() != FS_TYPE_FAT)
>                 return 0;
>
>         fs_close();
> @@ -428,10 +434,10 @@ static efi_status_t efi_disk_add_dev(
>
>         /*
>          * On partitions or whole disks without partitions install the
> -        * simple file system protocol if a file system is available.
> +        * simple file system protocol if a supported file system exists.
>          */
>         if ((part || desc->part_type == PART_TYPE_UNKNOWN) &&
> -           efi_fs_exists(desc, part)) {
> +           efi_supported_fs_exists(desc, part)) {
>                 diskobj->volume = efi_simple_file_system(desc, part,
>                                                          diskobj->dp);
>                 ret = efi_add_protocol(&diskobj->header,
>


-- 
Masami Hiramatsu