drivers/firmware/efi/efibc.c

// SPDX-License-Identifier: GPL-2.0
/*
 * efibc: control EFI bootloaders which obey LoaderEntryOneShot var
 * Copyright (c) 2013-2016, Intel Corporation.
 */

#define pr_fmt(fmt) "efibc: " fmt

#include <linux/efi.h>
#include <linux/module.h>
#include <linux/reboot.h>
#include <linux/slab.h>

static void efibc_str_to_str16(const char *str, efi_char16_t *str16)
{
	size_t i;

	for (i = 0; i < strlen(str); i++)
		str16[i] = str[i];

	str16[i] = '\0';
}

static int efibc_set_variable(const char *name, const char *value)
{
	int ret;
	efi_guid_t guid = LINUX_EFI_LOADER_ENTRY_GUID;
	struct efivar_entry *entry;
	size_t size = (strlen(value) + 1) * sizeof(efi_char16_t);

	if (size > sizeof(entry->var.Data)) {
		pr_err("value is too large (%zu bytes) for '%s' EFI variable\n", size, name);
		return -EINVAL;
	}

	entry = kmalloc(sizeof(*entry), GFP_KERNEL);
	if (!entry) {
		pr_err("failed to allocate efivar entry for '%s' EFI variable\n", name);
		return -ENOMEM;
	}

	efibc_str_to_str16(name, entry->var.VariableName);
	efibc_str_to_str16(value, (efi_char16_t *)entry->var.Data);
	memcpy(&entry->var.VendorGuid, &guid, sizeof(guid));

	ret = efivar_entry_set_safe(entry->var.VariableName,
				    entry->var.VendorGuid,
				    EFI_VARIABLE_NON_VOLATILE
				    | EFI_VARIABLE_BOOTSERVICE_ACCESS
				    | EFI_VARIABLE_RUNTIME_ACCESS,
				    false, size, entry->var.Data);

	if (ret)
		pr_err("failed to set %s EFI variable: 0x%x\n",
		       name, ret);

	kfree(entry);
	return ret;
}

static int efibc_reboot_notifier_call(struct notifier_block *notifier,
				      unsigned long event, void *data)
{
	const char *reason = "shutdown";
	int ret;

	if (event == SYS_RESTART)
		reason = "reboot";

	ret = efibc_set_variable("LoaderEntryRebootReason", reason);
	if (ret || !data)
		return NOTIFY_DONE;

	efibc_set_variable("LoaderEntryOneShot", (char *)data);

	return NOTIFY_DONE;
}

static struct notifier_block efibc_reboot_notifier = {
	.notifier_call = efibc_reboot_notifier_call,
};

static int __init efibc_init(void)
{
	int ret;

	if (!efivars_kobject() || !efivar_supports_writes())
		return -ENODEV;

	ret = register_reboot_notifier(&efibc_reboot_notifier);
	if (ret)
		pr_err("unable to register reboot notifier\n");

	return ret;
}
module_init(efibc_init);

static void __exit efibc_exit(void)
{
	unregister_reboot_notifier(&efibc_reboot_notifier);
}
module_exit(efibc_exit);

MODULE_AUTHOR("Jeremy Compostella <jeremy.compostella@intel.com>");
MODULE_AUTHOR("Matt Gumbel <matthew.k.gumbel@intel.com");
MODULE_DESCRIPTION("EFI Bootloader Control");
MODULE_LICENSE("GPL v2");