[PATCH 2/2] efi: libstub: Look for initrd LoadFile2 protocol on image handle

[Ard Biesheuvel <ardb@kernel.org>]

The use of a global singleton device path for describing the initrd to
be loaded by the kernel implies that only a single handle can exist that
carries the initrd LoadFile2 protocol implementation.

This avoids the need on the part of the EFI stub to reason about which
initrd is the preferred one when several are being provided - we already
have initrd loading via the setup header on x86 and via DT on other
architectures, in addition to the initrd= command line option, and so
having a single loader provided initrd that supersedes all of them was
deemed preferable over having multiple sources.

However, this means that intermediate loader stages cannot simply
install the LoadFile2 initrd device path, and will need to check for
failures and deal with them. It also means that such stages will have to
reason about whether or not the subsequent stage being loaded is the
final one, or whether it may attempt to install the initrd device path
itself.

We can solve this by associating the initrd LoadFile2 protocol with the
loaded image instead of with a global singleton device path. That way,
each stage can associate any initrd it provides with the image that it
is loading.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/libstub/efi-stub-helper.c | 42 ++++++++++++--------
 include/linux/efi.h                            |  2 +-
 include/linux/pe.h                             |  2 +-
 3 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index d47aa855398b39a6..a97c95a1d99e0b9d 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -482,10 +482,11 @@ static const struct {
 };
 
 /**
- * efi_load_initrd_dev_path() - load the initrd from the Linux initrd device path
- * @initrd:	pointer of struct to store the address where the initrd was loaded
- *		and the size of the loaded initrd
- * @max:	upper limit for the initrd memory allocation
+ * efi_load_initrd_lf2() - load the initrd from the Linux initrd device path
+ * @image_handle: EFI handle of the loaded image
+ * @initrd:	  pointer of struct to store the address where the initrd was
+ *                loaded and the size of the loaded initrd
+ * @max:	  upper limit for the initrd memory allocation
  *
  * Return:
  * * %EFI_SUCCESS if the initrd was loaded successfully, in which
@@ -495,24 +496,33 @@ static const struct {
  * * %EFI_LOAD_ERROR in all other cases
  */
 static
-efi_status_t efi_load_initrd_dev_path(struct linux_efi_initrd *initrd,
-				      unsigned long max)
+efi_status_t efi_load_initrd_lf2(efi_handle_t image_handle,
+				 struct linux_efi_initrd *initrd,
+				 unsigned long max)
 {
 	efi_guid_t lf2_proto_guid = EFI_LOAD_FILE2_PROTOCOL_GUID;
+	efi_guid_t initrd_lf2_proto_guid = LINUX_EFI_INITRD_LF2_PROTOCOL_GUID;
 	efi_device_path_protocol_t *dp;
 	efi_load_file2_protocol_t *lf2;
 	efi_handle_t handle;
 	efi_status_t status;
 
-	dp = (efi_device_path_protocol_t *)&initrd_dev_path;
-	status = efi_bs_call(locate_device_path, &lf2_proto_guid, &dp, &handle);
-	if (status != EFI_SUCCESS)
-		return status;
-
-	status = efi_bs_call(handle_protocol, handle, &lf2_proto_guid,
+	/* first look for a initrd loading protocol specific to this image */
+	status = efi_bs_call(handle_protocol, image_handle, &initrd_lf2_proto_guid,
 			     (void **)&lf2);
-	if (status != EFI_SUCCESS)
-		return status;
+	if (status != EFI_SUCCESS) {
+		/* look for the global singleton initrd loading protocol */
+		dp = (efi_device_path_protocol_t *)&initrd_dev_path;
+		status = efi_bs_call(locate_device_path, &lf2_proto_guid, &dp,
+				     &handle);
+		if (status != EFI_SUCCESS)
+			return status;
+
+		status = efi_bs_call(handle_protocol, handle, &lf2_proto_guid,
+				     (void **)&lf2);
+		if (status != EFI_SUCCESS)
+			return status;
+	}
 
 	initrd->size = 0;
 	status = efi_call_proto(lf2, load_file, dp, false, &initrd->size, NULL);
@@ -567,9 +577,9 @@ efi_status_t efi_load_initrd(efi_handle_t handle,
 	if (!IS_ENABLED(CONFIG_BLK_DEV_INITRD) || efi_noinitrd)
 		return EFI_SUCCESS;
 
-	status = efi_load_initrd_dev_path(&initrd, hard_limit);
+	status = efi_load_initrd_lf2(handle, &initrd, hard_limit);
 	if (status == EFI_SUCCESS) {
-		efi_info("Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path\n");
+		efi_info("Loaded initrd using LoadFile2 protocol\n");
 		if (initrd.size > 0 &&
 		    efi_measure_tagged_event(initrd.base, initrd.size,
 					     EFISTUB_EVT_INITRD) == EFI_SUCCESS)
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 04a733f0ba956211..83643d6aee755d85 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -417,7 +417,7 @@ void efi_native_runtime_setup(void);
 #define LINUX_EFI_MOK_VARIABLE_TABLE_GUID	EFI_GUID(0xc451ed2b, 0x9694, 0x45d3,  0xba, 0xba, 0xed, 0x9f, 0x89, 0x88, 0xa3, 0x89)
 #define LINUX_EFI_COCO_SECRET_AREA_GUID		EFI_GUID(0xadf956ad, 0xe98c, 0x484c,  0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47)
 #define LINUX_EFI_BOOT_MEMMAP_GUID		EFI_GUID(0x800f683f, 0xd08b, 0x423a,  0xa2, 0x93, 0x96, 0x5c, 0x3c, 0x6f, 0xe2, 0xb4)
-
+#define LINUX_EFI_INITRD_LF2_PROTOCOL_GUID	EFI_GUID(0xf9e3378e, 0xb3b1, 0x423a,  0xbd, 0x9a, 0x2d, 0x08, 0x60, 0x28, 0x7f, 0x72)
 #define RISCV_EFI_BOOT_PROTOCOL_GUID		EFI_GUID(0xccd15fec, 0x6f73, 0x4eec,  0x83, 0x95, 0x3e, 0x69, 0xe4, 0xb9, 0x40, 0xbf)
 
 /*
diff --git a/include/linux/pe.h b/include/linux/pe.h
index 6ffabf1e6d039e67..934e3a15ea7ddc07 100644
--- a/include/linux/pe.h
+++ b/include/linux/pe.h
@@ -29,7 +29,7 @@
  * handover_offset and xloadflags fields in the bootparams structure.
  */
 #define LINUX_EFISTUB_MAJOR_VERSION		0x1
-#define LINUX_EFISTUB_MINOR_VERSION		0x1
+#define LINUX_EFISTUB_MINOR_VERSION		0x2
 
 /*
  * LINUX_PE_MAGIC appears at offset 0x38 into the MS-DOS header of EFI bootable
-- 
2.39.2