efi_loader: pre-seed UEFI variables

Include a file with the initial values for non-volatile UEFI variables
into the U-Boot binary. If this variable is set, changes to variable PK
will not be allowed.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

include/asm-generic/sections.h

@@ -25,6 +25,8 @@ extern char __initdata_begin[], __initdata_end[];
 extern char __start_rodata[], __end_rodata[];
 extern char __efi_helloworld_begin[];
 extern char __efi_helloworld_end[];
+extern char __efi_var_file_begin[];
+extern char __efi_var_file_end[];
 
 /* Start and end of .ctors section - used for constructor calls. */
 extern char __ctors_start[], __ctors_end[];

include/efi_variable.h

@@ -138,6 +138,14 @@ struct efi_var_file {
  */
 efi_status_t efi_var_to_file(void);
 
+/**
+ * efi_var_restore() - restore EFI variables from buffer
+ *
+ * @buf:	buffer
+ * Return:	status code
+ */
+efi_status_t efi_var_restore(struct efi_var_file *buf);
+
 /**
  * efi_var_from_file() - read variables from file
  *

lib/efi_loader/Kconfig

@@ -50,6 +50,29 @@ config EFI_MM_COMM_TEE
 
 endchoice
 
+config EFI_VARIABLES_PRESEED
+	bool "Initial values for UEFI variables"
+	depends on EFI_VARIABLE_FILE_STORE
+	help
+	  Include a file with the initial values for non-volatile UEFI variables
+	  into the U-Boot binary. If this configuration option is set, changes
+	  to authentication related variables (PK, KEK, db, dbx) are not
+	  allowed.
+
+if EFI_VARIABLES_PRESEED
+
+config EFI_VAR_SEED_FILE
+	string "File with initial values of non-volatile UEFI variables"
+	default ubootefi.var
+	help
+	  File with initial values of non-volatile UEFI variables. The file must
+	  be in the same format as the storage in the EFI system partition. The
+	  easiest way to create it is by setting the non-volatile variables in
+	  U-Boot. If a relative file path is used, it is relative to the source
+	  directory.
+
+endif
+
 config EFI_GET_TIME
 	bool "GetTime() runtime service"
 	depends on DM_RTC

lib/efi_loader/Makefile

@@ -6,7 +6,7 @@
 # This file only gets included with CONFIG_EFI_LOADER set, so all
 # object inclusion implicitly depends on it
 
-asflags-y += -DHOST_ARCH="$(HOST_ARCH)"
+asflags-y += -DHOST_ARCH="$(HOST_ARCH)" -I.
 ccflags-y += -DHOST_ARCH="$(HOST_ARCH)"
 
 CFLAGS_efi_boottime.o += \
@@ -42,6 +42,7 @@ obj-y += efi_variable_tee.o
 else
 obj-y += efi_variable.o
 obj-y += efi_var_file.o
+obj-$(CONFIG_EFI_VARIABLES_PRESEED) += efi_var_seed.o
 endif
 obj-y += efi_watchdog.o
 obj-$(CONFIG_LCD) += efi_gop.o
@@ -53,3 +54,6 @@ obj-$(CONFIG_GENERATE_SMBIOS_TABLE) += efi_smbios.o
 obj-$(CONFIG_EFI_RNG_PROTOCOL) += efi_rng.o
 obj-$(CONFIG_EFI_LOAD_FILE2_INITRD) += efi_load_initrd.o
 obj-y += efi_signature.o
+
+EFI_VAR_SEED_FILE := $(subst $\",,$(CONFIG_EFI_VAR_SEED_FILE))
+$(obj)/efi_var_seed.o: $(srctree)/$(EFI_VAR_SEED_FILE)

lib/efi_loader/efi_var_file.c

@@ -159,13 +159,7 @@ error:
 #endif
 }
 
-/**
- * efi_var_restore() - restore EFI variables from buffer
- *
- * @buf:	buffer
- * Return:	status code
- */
-static efi_status_t __maybe_unused efi_var_restore(struct efi_var_file *buf)
+efi_status_t efi_var_restore(struct efi_var_file *buf)
 {
 	struct efi_var_entry *var, *last_var;
 	efi_status_t ret;

lib/efi_loader/efi_var_seed.S

@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Predefined UEFI variables
+ *
+ * Copyright (c) 2020, Heinrich Schuchardt <xypron.glpk@gmx.de>
+ */
+
+#include <config.h>
+
+.section .rodata.efi_seed.init,"a"
+.balign 16
+.global __efi_var_file_begin
+__efi_var_file_begin:
+.incbin CONFIG_EFI_VAR_SEED_FILE
+.global __efi_var_file_end
+__efi_var_file_end:
+.balign 16

lib/efi_loader/efi_variable.c

@@ -5,12 +5,15 @@
  * Copyright (c) 2017 Rob Clark
  */
 
+#define LOG_CATEGORY LOGC_EFI
+
 #include <common.h>
 #include <efi_loader.h>
 #include <efi_variable.h>
 #include <env.h>
 #include <env_internal.h>
 #include <hexdump.h>
+#include <log.h>
 #include <malloc.h>
 #include <rtc.h>
 #include <search.h>
@@ -18,7 +21,7 @@
 #include <crypto/pkcs7_parser.h>
 #include <linux/compat.h>
 #include <u-boot/crc.h>
-
+#include <asm/sections.h>
 
 #ifdef CONFIG_EFI_SECURE_BOOT
 static u8 pkcs7_hdr[] = {
@@ -365,10 +368,16 @@ efi_status_t efi_set_variable_int(u16 *variable_name, const efi_guid_t *vendor,
 	delete = !append && (!data_size || !attributes);
 
 	/* check attributes */
+	var_type = efi_auth_var_get_type(variable_name, vendor);
 	if (var) {
 		if (ro_check && (var->attr & EFI_VARIABLE_READ_ONLY))
 			return EFI_WRITE_PROTECTED;
 
+		if (IS_ENABLED(CONFIG_EFI_VARIABLES_PRESEED)) {
+			if (var_type != EFI_AUTH_VAR_NONE)
+				return EFI_WRITE_PROTECTED;
+		}
+
 		/* attributes won't be changed */
 		if (!delete &&
 		    ((ro_check && var->attr != attributes) ||
@@ -386,7 +395,6 @@ efi_status_t efi_set_variable_int(u16 *variable_name, const efi_guid_t *vendor,
 			return EFI_NOT_FOUND;
 	}
 
-	var_type = efi_auth_var_get_type(variable_name, vendor);
 	if (var_type != EFI_AUTH_VAR_NONE) {
 		/* authentication is mandatory */
 		if (!(attributes &
@@ -589,5 +597,12 @@ efi_status_t efi_init_variables(void)
 	if (ret != EFI_SUCCESS)
 		return ret;
 
+	if (IS_ENABLED(CONFIG_EFI_VARIABLES_PRESEED)) {
+		ret = efi_var_restore((struct efi_var_file *)
+				      __efi_var_file_begin);
+		if (ret != EFI_SUCCESS)
+			log_err("Invalid EFI variable seed\n");
+	}
+
 	return efi_var_from_file();
 }