efi: libstub: Implement devicepath support for initrd commandline loader

Currently, the initrd= command line option to the EFI stub only supports
loading files that reside on the same volume as the loaded image, which
is not workable for loaders like GRUB that don't even implement the
volume abstraction (EFI_SIMPLE_FILE_SYSTEM_PROTOCOL), and load the
kernel from an anonymous buffer in memory. For this reason, another
method was devised that relies on the LoadFile2 protocol.

However, the command line loader is rather useful when using the UEFI
shell or other generic loaders that have no awareness of Linux specific
protocols so let's make it a bit more flexible, by permitting textual
device paths to be provided to initrd= as well, provided that they refer
to a file hosted on a EFI_SIMPLE_FILE_SYSTEM_PROTOCOL volume. E.g.,

  initrd=PciRoot(0x0)/Pci(0x3,0x0)/HD(1,MBR,0xBE1AFDFA,0x3F,0xFBFC1)/rootfs.cpio.gz

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
index e85916ed5311..1fde9cbe6899 100644
--- a/drivers/firmware/efi/libstub/efistub.h
+++ b/drivers/firmware/efi/libstub/efistub.h
@@ -179,6 +179,21 @@ union efi_device_path_to_text_protocol {
 
 typedef union efi_device_path_to_text_protocol efi_device_path_to_text_protocol_t;
 
+union efi_device_path_from_text_protocol {
+	struct {
+		efi_device_path_protocol_t *
+			(__efiapi *convert_text_to_device_node)(const efi_char16_t *);
+		efi_device_path_protocol_t *
+			(__efiapi *convert_text_to_device_path)(const efi_char16_t *);
+	};
+	struct {
+		u32 convert_text_to_device_node;
+		u32 convert_text_to_device_path;
+	} mixed_mode;
+};
+
+typedef union efi_device_path_from_text_protocol efi_device_path_from_text_protocol_t;
+
 typedef void *efi_event_t;
 /* Note that notifications won't work in mixed mode */
 typedef void (__efiapi *efi_event_notify_t)(efi_event_t, void *);