efi: libstub: remove DT dependency from generic stub

Refactor the generic EFI stub entry code so that all the dependencies on
device tree are abstracted and hidden behind a generic efi_boot_kernel()
routine that can also be implemented in other ways. This allows users of
the generic stub to avoid using FDT for passing information to the core
kernel.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/efi-stub.c

@@ -10,7 +10,6 @@
  */
 
 #include <linux/efi.h>
-#include <linux/libfdt.h>
 #include <asm/efi.h>
 
 #include "efistub.h"
@@ -132,14 +131,11 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 	unsigned long image_addr;
 	unsigned long image_size = 0;
 	/* addr/point and size pairs for memory management*/
-	unsigned long fdt_addr = 0;  /* Original DTB */
-	unsigned long fdt_size = 0;
 	char *cmdline_ptr = NULL;
 	int cmdline_size = 0;
 	efi_guid_t loaded_image_proto = LOADED_IMAGE_PROTOCOL_GUID;
 	unsigned long reserve_addr = 0;
 	unsigned long reserve_size = 0;
-	enum efi_secureboot_mode secure_boot;
 	struct screen_info *si;
 	efi_properties_table_t *prop_tbl;
 
@@ -215,38 +211,6 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 	/* Ask the firmware to clear memory on unclean shutdown */
 	efi_enable_reset_attack_mitigation();
 
-	secure_boot = efi_get_secureboot();
-
-	/*
-	 * Unauthenticated device tree data is a security hazard, so ignore
-	 * 'dtb=' unless UEFI Secure Boot is disabled.  We assume that secure
-	 * boot is enabled if we can't determine its state.
-	 */
-	if (!IS_ENABLED(CONFIG_EFI_ARMSTUB_DTB_LOADER) ||
-	     secure_boot != efi_secureboot_mode_disabled) {
-		if (strstr(cmdline_ptr, "dtb="))
-			efi_err("Ignoring DTB from command line.\n");
-	} else {
-		status = efi_load_dtb(image, &fdt_addr, &fdt_size);
-
-		if (status != EFI_SUCCESS && status != EFI_NOT_READY) {
-			efi_err("Failed to load device tree!\n");
-			goto fail_free_image;
-		}
-	}
-
-	if (fdt_addr) {
-		efi_info("Using DTB from command line\n");
-	} else {
-		/* Look for a device tree configuration table entry. */
-		fdt_addr = (uintptr_t)get_fdt(&fdt_size);
-		if (fdt_addr)
-			efi_info("Using DTB from configuration table\n");
-	}
-
-	if (!fdt_addr)
-		efi_info("Generating empty DTB\n");
-
 	efi_load_initrd(image, ULONG_MAX, efi_get_max_initrd_addr(image_addr),
 			NULL);
 
@@ -290,23 +254,8 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
 
 	install_memreserve_table();
 
-	status = allocate_new_fdt_and_exit_boot(handle, &fdt_addr, cmdline_ptr,
-						fdt_addr, fdt_size);
-	if (status != EFI_SUCCESS)
-		goto fail_free_fdt;
-
-	if (IS_ENABLED(CONFIG_ARM))
-		efi_handle_post_ebs_state();
-
-	efi_enter_kernel(image_addr, fdt_addr, fdt_totalsize((void *)fdt_addr));
-	/* not reached */
-
-fail_free_fdt:
-	efi_err("Failed to update FDT and exit boot services\n");
-
-	efi_free(fdt_size, fdt_addr);
+	status = efi_boot_kernel(handle, image, image_addr, cmdline_ptr);
 
-fail_free_image:
 	efi_free(image_size, image_addr);
 	efi_free(reserve_size, reserve_addr);
 fail_free_screeninfo:

drivers/firmware/efi/libstub/efistub.h

@@ -844,11 +844,8 @@ typedef efi_status_t (*efi_exit_boot_map_processing)(
 efi_status_t efi_exit_boot_services(void *handle, void *priv,
 				    efi_exit_boot_map_processing priv_func);
 
-efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
-					    unsigned long *new_fdt_addr,
-					    char *cmdline_ptr,
-					    unsigned long fdt_addr,
-					    unsigned long fdt_size);
+efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
+			     unsigned long kernel_addr, char *cmdline_ptr);
 
 void *get_fdt(unsigned long *fdt_size);
 

drivers/firmware/efi/libstub/fdt.c

@@ -219,17 +219,18 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map, void *priv)
  * exit_boot_services() call, so the exiting of boot services is very tightly
  * tied to the creation of the FDT with the final memory map in it.
  */
-
+static
 efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
+					    efi_loaded_image_t *image,
 					    unsigned long *new_fdt_addr,
-					    char *cmdline_ptr,
-					    unsigned long fdt_addr,
-					    unsigned long fdt_size)
+					    char *cmdline_ptr)
 {
 	unsigned long desc_size;
 	u32 desc_ver;
 	efi_status_t status;
 	struct exit_boot_struct priv;
+	unsigned long fdt_addr = 0;
+	unsigned long fdt_size = 0;
 
 	if (!efi_novamap) {
 		status = efi_alloc_virtmap(&priv.runtime_map, &desc_size,
@@ -240,6 +241,36 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 		}
 	}
 
+	/*
+	 * Unauthenticated device tree data is a security hazard, so ignore
+	 * 'dtb=' unless UEFI Secure Boot is disabled.  We assume that secure
+	 * boot is enabled if we can't determine its state.
+	 */
+	if (!IS_ENABLED(CONFIG_EFI_ARMSTUB_DTB_LOADER) ||
+	    efi_get_secureboot() != efi_secureboot_mode_disabled) {
+		if (strstr(cmdline_ptr, "dtb="))
+			efi_err("Ignoring DTB from command line.\n");
+	} else {
+		status = efi_load_dtb(image, &fdt_addr, &fdt_size);
+
+		if (status != EFI_SUCCESS && status != EFI_NOT_READY) {
+			efi_err("Failed to load device tree!\n");
+			goto fail;
+		}
+	}
+
+	if (fdt_addr) {
+		efi_info("Using DTB from command line\n");
+	} else {
+		/* Look for a device tree configuration table entry. */
+		fdt_addr = (uintptr_t)get_fdt(&fdt_size);
+		if (fdt_addr)
+			efi_info("Using DTB from configuration table\n");
+	}
+
+	if (!fdt_addr)
+		efi_info("Generating empty DTB\n");
+
 	efi_info("Exiting boot services...\n");
 
 	status = efi_allocate_pages(MAX_FDT_SIZE, new_fdt_addr, ULONG_MAX);
@@ -303,11 +334,33 @@ efi_status_t allocate_new_fdt_and_exit_boot(void *handle,
 	efi_free(MAX_FDT_SIZE, *new_fdt_addr);
 
 fail:
+	efi_free(fdt_size, fdt_addr);
+
 	efi_bs_call(free_pool, priv.runtime_map);
 
 	return EFI_LOAD_ERROR;
 }
 
+efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
+			     unsigned long kernel_addr, char *cmdline_ptr)
+{
+	unsigned long fdt_addr;
+	efi_status_t status;
+
+	status = allocate_new_fdt_and_exit_boot(handle, image, &fdt_addr,
+						cmdline_ptr);
+	if (status != EFI_SUCCESS) {
+		efi_err("Failed to update FDT and exit boot services\n");
+		return status;
+	}
+
+	if (IS_ENABLED(CONFIG_ARM))
+		efi_handle_post_ebs_state();
+
+	efi_enter_kernel(kernel_addr, fdt_addr, fdt_totalsize((void *)fdt_addr));
+	/* not reached */
+}
+
 void *get_fdt(unsigned long *fdt_size)
 {
 	void *fdt;