lib/efi_loader/efi_var_common.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * UEFI runtime variable services
 *
 * Copyright (c) 2020, Heinrich Schuchardt <xypron.glpk@gmx.de>
 */

#include <common.h>
#include <efi_loader.h>
#include <efi_variable.h>

enum efi_secure_mode {
	EFI_MODE_SETUP,
	EFI_MODE_USER,
	EFI_MODE_AUDIT,
	EFI_MODE_DEPLOYED,
};

static bool efi_secure_boot;
static enum efi_secure_mode efi_secure_mode;

/**
 * efi_efi_get_variable() - retrieve value of a UEFI variable
 *
 * This function implements the GetVariable runtime service.
 *
 * See the Unified Extensible Firmware Interface (UEFI) specification for
 * details.
 *
 * @variable_name:	name of the variable
 * @vendor:		vendor GUID
 * @attributes:		attributes of the variable
 * @data_size:		size of the buffer to which the variable value is copied
 * @data:		buffer to which the variable value is copied
 * Return:		status code
 */
efi_status_t EFIAPI efi_get_variable(u16 *variable_name,
				     const efi_guid_t *vendor, u32 *attributes,
				     efi_uintn_t *data_size, void *data)
{
	efi_status_t ret;

	EFI_ENTRY("\"%ls\" %pUl %p %p %p", variable_name, vendor, attributes,
		  data_size, data);

	ret = efi_get_variable_int(variable_name, vendor, attributes,
				   data_size, data, NULL);

	/* Remove EFI_VARIABLE_READ_ONLY flag */
	if (attributes)
		*attributes &= EFI_VARIABLE_MASK;

	return EFI_EXIT(ret);
}

/**
 * efi_set_variable() - set value of a UEFI variable
 *
 * This function implements the SetVariable runtime service.
 *
 * See the Unified Extensible Firmware Interface (UEFI) specification for
 * details.
 *
 * @variable_name:	name of the variable
 * @vendor:		vendor GUID
 * @attributes:		attributes of the variable
 * @data_size:		size of the buffer with the variable value
 * @data:		buffer with the variable value
 * Return:		status code
 */
efi_status_t EFIAPI efi_set_variable(u16 *variable_name,
				     const efi_guid_t *vendor, u32 attributes,
				     efi_uintn_t data_size, const void *data)
{
	efi_status_t ret;

	EFI_ENTRY("\"%ls\" %pUl %x %zu %p", variable_name, vendor, attributes,
		  data_size, data);

	/* Make sure that the EFI_VARIABLE_READ_ONLY flag is not set */
	if (attributes & ~(u32)EFI_VARIABLE_MASK)
		ret = EFI_INVALID_PARAMETER;
	else
		ret = efi_set_variable_int(variable_name, vendor, attributes,
					   data_size, data, true);

	return EFI_EXIT(ret);
}

/**
 * efi_get_next_variable_name() - enumerate the current variable names
 *
 * @variable_name_size:	size of variable_name buffer in byte
 * @variable_name:	name of uefi variable's name in u16
 * @vendor:		vendor's guid
 *
 * See the Unified Extensible Firmware Interface (UEFI) specification for
 * details.
 *
 * Return: status code
 */
efi_status_t EFIAPI efi_get_next_variable_name(efi_uintn_t *variable_name_size,
					       u16 *variable_name,
					       efi_guid_t *vendor)
{
	efi_status_t ret;

	EFI_ENTRY("%p \"%ls\" %pUl", variable_name_size, variable_name, vendor);

	ret = efi_get_next_variable_name_int(variable_name_size, variable_name,
					     vendor);

	return EFI_EXIT(ret);
}

/**
 * efi_query_variable_info() - get information about EFI variables
 *
 * This function implements the QueryVariableInfo() runtime service.
 *
 * See the Unified Extensible Firmware Interface (UEFI) specification for
 * details.
 *
 * @attributes:				bitmask to select variables to be
 *					queried
 * @maximum_variable_storage_size:	maximum size of storage area for the
 *					selected variable types
 * @remaining_variable_storage_size:	remaining size of storage are for the
 *					selected variable types
 * @maximum_variable_size:		maximum size of a variable of the
 *					selected type
 * Returns:				status code
 */
efi_status_t EFIAPI efi_query_variable_info(
			u32 attributes, u64 *maximum_variable_storage_size,
			u64 *remaining_variable_storage_size,
			u64 *maximum_variable_size)
{
	efi_status_t ret;

	EFI_ENTRY("%x %p %p %p", attributes, maximum_variable_storage_size,
		  remaining_variable_storage_size, maximum_variable_size);

	ret = efi_query_variable_info_int(attributes,
					  maximum_variable_storage_size,
					  remaining_variable_storage_size,
					  maximum_variable_size);

	return EFI_EXIT(ret);
}

/**
 * efi_set_secure_state - modify secure boot state variables
 * @secure_boot:	value of SecureBoot
 * @setup_mode:		value of SetupMode
 * @audit_mode:		value of AuditMode
 * @deployed_mode:	value of DeployedMode
 *
 * Modify secure boot status related variables as indicated.
 *
 * Return:		status code
 */
static efi_status_t efi_set_secure_state(u8 secure_boot, u8 setup_mode,
					 u8 audit_mode, u8 deployed_mode)
{
	efi_status_t ret;
	const u32 attributes_ro = EFI_VARIABLE_BOOTSERVICE_ACCESS |
				  EFI_VARIABLE_RUNTIME_ACCESS |
				  EFI_VARIABLE_READ_ONLY;
	const u32 attributes_rw = EFI_VARIABLE_BOOTSERVICE_ACCESS |
				  EFI_VARIABLE_RUNTIME_ACCESS;

	efi_secure_boot = secure_boot;

	ret = efi_set_variable_int(L"SecureBoot", &efi_global_variable_guid,
				   attributes_ro, sizeof(secure_boot),
				   &secure_boot, false);
	if (ret != EFI_SUCCESS)
		goto err;

	ret = efi_set_variable_int(L"SetupMode", &efi_global_variable_guid,
				   attributes_ro, sizeof(setup_mode),
				   &setup_mode, false);
	if (ret != EFI_SUCCESS)
		goto err;

	ret = efi_set_variable_int(L"AuditMode", &efi_global_variable_guid,
				   audit_mode || setup_mode ?
				   attributes_ro : attributes_rw,
				   sizeof(audit_mode), &audit_mode, false);
	if (ret != EFI_SUCCESS)
		goto err;

	ret = efi_set_variable_int(L"DeployedMode",
				   &efi_global_variable_guid,
				   audit_mode || deployed_mode || setup_mode ?
				   attributes_ro : attributes_rw,
				   sizeof(deployed_mode), &deployed_mode,
				   false);
err:
	return ret;
}

/**
 * efi_transfer_secure_state - handle a secure boot state transition
 * @mode:	new state
 *
 * Depending on @mode, secure boot related variables are updated.
 * Those variables are *read-only* for users, efi_set_variable_int()
 * is called here.
 *
 * Return:	status code
 */
static efi_status_t efi_transfer_secure_state(enum efi_secure_mode mode)
{
	efi_status_t ret;

	EFI_PRINT("Switching secure state from %d to %d\n", efi_secure_mode,
		  mode);

	if (mode == EFI_MODE_DEPLOYED) {
		ret = efi_set_secure_state(1, 0, 0, 1);
		if (ret != EFI_SUCCESS)
			goto err;
	} else if (mode == EFI_MODE_AUDIT) {
		ret = efi_set_variable_int(L"PK", &efi_global_variable_guid,
					   EFI_VARIABLE_BOOTSERVICE_ACCESS |
					   EFI_VARIABLE_RUNTIME_ACCESS,
					   0, NULL, false);
		if (ret != EFI_SUCCESS)
			goto err;

		ret = efi_set_secure_state(0, 1, 1, 0);
		if (ret != EFI_SUCCESS)
			goto err;
	} else if (mode == EFI_MODE_USER) {
		ret = efi_set_secure_state(1, 0, 0, 0);
		if (ret != EFI_SUCCESS)
			goto err;
	} else if (mode == EFI_MODE_SETUP) {
		ret = efi_set_secure_state(0, 1, 0, 0);
		if (ret != EFI_SUCCESS)
			goto err;
	} else {
		return EFI_INVALID_PARAMETER;
	}

	efi_secure_mode = mode;

	return EFI_SUCCESS;

err:
	/* TODO: What action should be taken here? */
	printf("ERROR: Secure state transition failed\n");
	return ret;
}

efi_status_t efi_init_secure_state(void)
{
	enum efi_secure_mode mode = EFI_MODE_SETUP;
	u8 efi_vendor_keys = 0;
	efi_uintn_t size = 0;
	efi_status_t ret;

	ret = efi_get_variable_int(L"PK", &efi_global_variable_guid,
				   NULL, &size, NULL, NULL);
	if (ret == EFI_BUFFER_TOO_SMALL) {
		if (IS_ENABLED(CONFIG_EFI_SECURE_BOOT))
			mode = EFI_MODE_USER;
	}

	ret = efi_transfer_secure_state(mode);
	if (ret != EFI_SUCCESS)
		return ret;

	/* As we do not provide vendor keys this variable is always 0. */
	ret = efi_set_variable_int(L"VendorKeys",
				   &efi_global_variable_guid,
				   EFI_VARIABLE_BOOTSERVICE_ACCESS |
				   EFI_VARIABLE_RUNTIME_ACCESS |
				   EFI_VARIABLE_READ_ONLY,
				   sizeof(efi_vendor_keys),
				   &efi_vendor_keys, false);
	return ret;
}

/**
 * efi_secure_boot_enabled - return if secure boot is enabled or not
 *
 * Return:	true if enabled, false if disabled
 */
bool efi_secure_boot_enabled(void)
{
	return efi_secure_boot;
}