efi_loader: UEFI variable persistence

Persist non-volatile UEFI variables in a file on the EFI system partition.

The file is written whenever a non-volatile UEFI variable is changed after
initialization of the UEFI sub-system.

The file is read during the UEFI sub-system initialization to restore
non-volatile UEFI variables.

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

include/efi_variable.h

@@ -79,4 +79,66 @@ efi_status_t efi_query_variable_info_int(u32 attributes,
 					 u64 *remaining_variable_storage_size,
 					 u64 *maximum_variable_size);
 
+#define EFI_VAR_FILE_NAME "ubootefi.var"
+
+#define EFI_VAR_BUF_SIZE 0x4000
+
+#define EFI_VAR_FILE_MAGIC 0x0161566966456255 /* UbEfiVa, version 1 */
+
+/**
+ * struct efi_var_entry - UEFI variable file entry
+ *
+ * @length:	length of enty, multiple of 8
+ * @attr:	variable attributes
+ * @time:	authentication time (seconds since start of epoch)
+ * @guid:	vendor GUID
+ * @name:	UTF16 variable name
+ */
+struct efi_var_entry {
+	u32 length;
+	u32 attr;
+	u64 time;
+	efi_guid_t guid;
+	u16 name[];
+};
+
+/**
+ * struct efi_var_file - file for storing UEFI variables
+ *
+ * @reserved:	unused, may be overwritten by memory probing
+ * @magic:	identifies file format
+ * @length:	length including header
+ * @crc32:	CRC32 without header
+ * @var:	variables
+ */
+struct efi_var_file {
+	u64 reserved;
+	u64 magic;
+	u32 length;
+	u32 crc32;
+	struct efi_var_entry var[];
+};
+
+/**
+ * efi_var_to_file() - save non-volatile variables as file
+ *
+ * File ubootefi.var is created on the EFI system partion.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_var_to_file(void);
+
+/**
+ * efi_var_from_file() - read variables from file
+ *
+ * File ubootefi.var is read from the EFI system partitions and the variables
+ * stored in the file are created.
+ *
+ * In case the file does not exist yet or a variable cannot be set EFI_SUCCESS
+ * is returned.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_var_from_file(void);
+
 #endif

lib/efi_loader/Kconfig

@@ -27,6 +27,14 @@ config EFI_LOADER
 
 if EFI_LOADER
 
+config EFI_VARIABLE_FILE_STORE
+	bool "Store non-volatile UEFI variables as file"
+	depends on FAT_WRITE
+	default y
+	help
+	  Select tis option if you want non-volatile UEFI variables to be stored
+	  as file /ubootefi.var on the EFI system partition.
+
 config EFI_GET_TIME
 	bool "GetTime() runtime service"
 	depends on DM_RTC

lib/efi_loader/Makefile

@@ -40,6 +40,7 @@ ifeq ($(CONFIG_EFI_MM_COMM_TEE),y)
 obj-y += efi_variable_tee.o
 else
 obj-y += efi_variable.o
+obj-y += efi_var_file.o
 endif
 obj-y += efi_watchdog.o
 obj-$(CONFIG_LCD) += efi_gop.o

lib/efi_loader/efi_var_file.c

@@ -0,0 +1,239 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * File interface for UEFI variables
+ *
+ * Copyright (c) 2020, Heinrich Schuchardt
+ */
+
+#define LOG_CATEGORY LOGC_EFI
+
+#include <common.h>
+#include <charset.h>
+#include <fs.h>
+#include <log.h>
+#include <malloc.h>
+#include <mapmem.h>
+#include <efi_loader.h>
+#include <efi_variable.h>
+#include <u-boot/crc.h>
+
+#define PART_STR_LEN 10
+
+/**
+ * efi_set_blk_dev_to_system_partition() - select EFI system partition
+ *
+ * Set the EFI system partition as current block device.
+ *
+ * Return:	status code
+ */
+static efi_status_t __maybe_unused efi_set_blk_dev_to_system_partition(void)
+{
+	char part_str[PART_STR_LEN];
+	int r;
+
+	if (!efi_system_partition.if_type) {
+		log_err("No EFI system partition\n");
+		return EFI_DEVICE_ERROR;
+	}
+	snprintf(part_str, PART_STR_LEN, "%u:%u",
+		 efi_system_partition.devnum, efi_system_partition.part);
+	r = fs_set_blk_dev(blk_get_if_type_name(efi_system_partition.if_type),
+			   part_str, FS_TYPE_ANY);
+	if (r) {
+		log_err("Cannot read EFI system partition\n");
+		return EFI_DEVICE_ERROR;
+	}
+	return EFI_SUCCESS;
+}
+
+/**
+ * efi_var_collect() - collect non-volatile variables in buffer
+ *
+ * A buffer is allocated and filled with all non-volatile variables in a
+ * format ready to be written to disk.
+ *
+ * @bufp:	pointer to pointer of buffer with collected variables
+ * @lenp:	pointer to length of buffer
+ * Return:	status code
+ */
+static efi_status_t __maybe_unused efi_var_collect(struct efi_var_file **bufp,
+						   loff_t *lenp)
+{
+	size_t len = EFI_VAR_BUF_SIZE;
+	struct efi_var_file *buf;
+	struct efi_var_entry *var, *old_var;
+	size_t old_var_name_length = 2;
+
+	*bufp = NULL; /* Avoid double free() */
+	buf = calloc(1, len);
+	if (!buf)
+		return EFI_OUT_OF_RESOURCES;
+	var = buf->var;
+	old_var = var;
+	for (;;) {
+		efi_uintn_t data_length, var_name_length;
+		u8 *data;
+		efi_status_t ret;
+
+		if ((uintptr_t)buf + len <=
+		    (uintptr_t)var->name + old_var_name_length)
+			return EFI_BUFFER_TOO_SMALL;
+
+		var_name_length = (uintptr_t)buf + len - (uintptr_t)var->name;
+		memcpy(var->name, old_var->name, old_var_name_length);
+		guidcpy(&var->guid, &old_var->guid);
+		ret = efi_get_next_variable_name_int(
+				&var_name_length, var->name, &var->guid);
+		if (ret == EFI_NOT_FOUND)
+			break;
+		if (ret != EFI_SUCCESS) {
+			free(buf);
+			return ret;
+		}
+		old_var_name_length = var_name_length;
+		old_var = var;
+
+		data = (u8 *)var->name + old_var_name_length;
+		data_length = (uintptr_t)buf + len - (uintptr_t)data;
+		ret = efi_get_variable_int(var->name, &var->guid,
+					   &var->attr, &data_length, data,
+					   &var->time);
+		if (ret != EFI_SUCCESS) {
+			free(buf);
+			return ret;
+		}
+		if (!(var->attr & EFI_VARIABLE_NON_VOLATILE))
+			continue;
+		var->length = data_length;
+		var = (struct efi_var_entry *)
+		      ALIGN((uintptr_t)data + data_length, 8);
+	}
+
+	buf->reserved = 0;
+	buf->magic = EFI_VAR_FILE_MAGIC;
+	len = (uintptr_t)var - (uintptr_t)buf;
+	buf->crc32 = crc32(0, (u8 *)buf->var,
+			   len - sizeof(struct efi_var_file));
+	buf->length = len;
+	*bufp = buf;
+	*lenp = len;
+
+	return EFI_SUCCESS;
+}
+
+/**
+ * efi_var_to_file() - save non-volatile variables as file
+ *
+ * File ubootefi.var is created on the EFI system partion.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_var_to_file(void)
+{
+#ifdef CONFIG_EFI_VARIABLE_FILE_STORE
+	efi_status_t ret;
+	struct efi_var_file *buf;
+	loff_t len;
+	loff_t actlen;
+	int r;
+
+	ret = efi_var_collect(&buf, &len);
+	if (ret != EFI_SUCCESS)
+		goto error;
+
+	ret = efi_set_blk_dev_to_system_partition();
+	if (ret != EFI_SUCCESS)
+		goto error;
+
+	r = fs_write(EFI_VAR_FILE_NAME, map_to_sysmem(buf), 0, len, &actlen);
+	if (r || len != actlen)
+		ret = EFI_DEVICE_ERROR;
+
+error:
+	if (ret != EFI_SUCCESS)
+		log_err("Failed to persist EFI variables\n");
+	free(buf);
+	return ret;
+#else
+	return EFI_SUCCESS;
+#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)
+{
+	struct efi_var_entry *var, *last_var;
+	efi_status_t ret;
+
+	if (buf->reserved || buf->magic != EFI_VAR_FILE_MAGIC ||
+	    buf->crc32 != crc32(0, (u8 *)buf->var,
+				buf->length - sizeof(struct efi_var_file))) {
+		log_err("Invalid EFI variables file\n");
+		return EFI_INVALID_PARAMETER;
+	}
+
+	var = buf->var;
+	last_var = (struct efi_var_entry *)((u8 *)buf + buf->length);
+	while (var < last_var) {
+		u16 *data = var->name + u16_strlen(var->name) + 1;
+
+		if (var->attr & EFI_VARIABLE_NON_VOLATILE && var->length) {
+			ret = efi_set_variable_int(var->name, &var->guid,
+						   var->attr, var->length,
+						   data, true);
+			if (ret != EFI_SUCCESS)
+				log_err("Failed to set EFI variable %ls\n",
+					var->name);
+		}
+		var = (struct efi_var_entry *)
+		      ALIGN((uintptr_t)data + var->length, 8);
+	}
+	return EFI_SUCCESS;
+}
+
+/**
+ * efi_var_from_file() - read variables from file
+ *
+ * File ubootefi.var is read from the EFI system partitions and the variables
+ * stored in the file are created.
+ *
+ * In case the file does not exist yet or a variable cannot be set EFI_SUCCESS
+ * is returned.
+ *
+ * Return:	status code
+ */
+efi_status_t efi_var_from_file(void)
+{
+#ifdef CONFIG_EFI_VARIABLE_FILE_STORE
+	struct efi_var_file *buf;
+	loff_t len;
+	efi_status_t ret;
+	int r;
+
+	buf = calloc(1, EFI_VAR_BUF_SIZE);
+	if (!buf) {
+		log_err("Out of memory\n");
+		return EFI_OUT_OF_RESOURCES;
+	}
+
+	ret = efi_set_blk_dev_to_system_partition();
+	if (ret != EFI_SUCCESS)
+		goto error;
+	r = fs_read(EFI_VAR_FILE_NAME, map_to_sysmem(buf), 0, EFI_VAR_BUF_SIZE,
+		    &len);
+	if (r || len < sizeof(struct efi_var_file)) {
+		log_err("Failed to load EFI variables\n");
+		goto error;
+	}
+	if (buf->length != len || efi_var_restore(buf) != EFI_SUCCESS)
+		log_err("Invalid EFI variables file\n");
+error:
+	free(buf);
+#endif
+	return EFI_SUCCESS;
+}

lib/efi_loader/efi_variable.c

@@ -988,6 +988,11 @@ out:
 			ret = EFI_SUCCESS;
 	}
 
+	/* Write non-volatile EFI variables to file */
+	if (attributes & EFI_VARIABLE_NON_VOLATILE &&
+	    ret == EFI_SUCCESS && efi_obj_list_initialized == EFI_SUCCESS)
+		efi_var_to_file();
+
 err:
 	free(native_name);
 	free(old_data);
@@ -1083,6 +1088,7 @@ efi_set_variable_runtime(u16 *variable_name, const efi_guid_t *vendor,
  */
 void efi_variables_boot_exit_notify(void)
 {
+	/* Switch variable services functions to runtime version */
 	efi_runtime_services.get_variable = efi_get_variable_runtime;
 	efi_runtime_services.get_next_variable_name =
 				efi_get_next_variable_name_runtime;
@@ -1102,6 +1108,8 @@ efi_status_t efi_init_variables(void)
 	efi_status_t ret;
 
 	ret = efi_init_secure_state();
+	if (ret != EFI_SUCCESS)
+		return ret;
 
-	return ret;
+	return efi_var_from_file();
 }