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

[Heinrich Schuchardt]

Am 3. Juni 2021 04:17:56 MESZ schrieb 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.
>

Does the UEFI spec forbid to access to other file systems?

Which problems were observed?

Best regards

Heinrich


>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,