lib/efi_loader/efi_bootmgr.c

// SPDX-License-Identifier: GPL-2.0+
/*
 *  EFI boot manager
 *
 *  Copyright (c) 2017 Rob Clark
 */

#define LOG_CATEGORY LOGC_EFI

#include <common.h>
#include <charset.h>
#include <log.h>
#include <malloc.h>
#include <efi_loader.h>
#include <efi_variable.h>
#include <asm/unaligned.h>

static const struct efi_boot_services *bs;
static const struct efi_runtime_services *rs;

/*
 * bootmgr implements the logic of trying to find a payload to boot
 * based on the BootOrder + BootXXXX variables, and then loading it.
 *
 * TODO detecting a special key held (f9?) and displaying a boot menu
 * like you would get on a PC would be clever.
 *
 * TODO if we had a way to write and persist variables after the OS
 * has started, we'd also want to check OsIndications to see if we
 * should do normal or recovery boot.
 */

/**
 * get_var() - get UEFI variable
 *
 * It is the caller's duty to free the returned buffer.
 *
 * @name:	name of variable
 * @vendor:	vendor GUID of variable
 * @size:	size of allocated buffer
 * Return:	buffer with variable data or NULL
 */
static void *get_var(u16 *name, const efi_guid_t *vendor,
		     efi_uintn_t *size)
{
	efi_status_t ret;
	void *buf = NULL;

	*size = 0;
	ret = efi_get_variable_int(name, vendor, NULL, size, buf, NULL);
	if (ret == EFI_BUFFER_TOO_SMALL) {
		buf = malloc(*size);
		ret = efi_get_variable_int(name, vendor, NULL, size, buf, NULL);
	}

	if (ret != EFI_SUCCESS) {
		free(buf);
		*size = 0;
		return NULL;
	}

	return buf;
}

/**
 * try_load_entry() - try to load image for boot option
 *
 * Attempt to load load-option number 'n', returning device_path and file_path
 * if successful. This checks that the EFI_LOAD_OPTION is active (enabled)
 * and that the specified file to boot exists.
 *
 * @n:			number of the boot option, e.g. 0x0a13 for Boot0A13
 * @handle:		on return handle for the newly installed image
 * @load_options:	load options set on the loaded image protocol
 * Return:		status code
 */
static efi_status_t try_load_entry(u16 n, efi_handle_t *handle,
				   void **load_options)
{
	struct efi_load_option lo;
	u16 varname[] = L"Boot0000";
	u16 hexmap[] = L"0123456789ABCDEF";
	void *load_option;
	efi_uintn_t size;
	efi_status_t ret;

	varname[4] = hexmap[(n & 0xf000) >> 12];
	varname[5] = hexmap[(n & 0x0f00) >> 8];
	varname[6] = hexmap[(n & 0x00f0) >> 4];
	varname[7] = hexmap[(n & 0x000f) >> 0];

	load_option = get_var(varname, &efi_global_variable_guid, &size);
	if (!load_option)
		return EFI_LOAD_ERROR;

	ret = efi_deserialize_load_option(&lo, load_option, &size);
	if (ret != EFI_SUCCESS) {
		log_warning("Invalid load option for %ls\n", varname);
		goto error;
	}

	if (lo.attributes & LOAD_OPTION_ACTIVE) {
		u32 attributes;

		log_debug("%s: trying to load \"%ls\" from %pD\n",
			  __func__, lo.label, lo.file_path);

		ret = EFI_CALL(efi_load_image(true, efi_root, lo.file_path,
					      NULL, 0, handle));
		if (ret != EFI_SUCCESS) {
			log_warning("Loading %ls '%ls' failed\n",
				    varname, lo.label);
			goto error;
		}

		attributes = EFI_VARIABLE_BOOTSERVICE_ACCESS |
			     EFI_VARIABLE_RUNTIME_ACCESS;
		ret = efi_set_variable_int(L"BootCurrent",
					   &efi_global_variable_guid,
					   attributes, sizeof(n), &n, false);
		if (ret != EFI_SUCCESS) {
			if (EFI_CALL(efi_unload_image(*handle))
			    != EFI_SUCCESS)
				log_err("Unloading image failed\n");
			goto error;
		}

		log_info("Booting: %ls\n", lo.label);
	} else {
		ret = EFI_LOAD_ERROR;
	}

	/* Set load options */
	if (size) {
		*load_options = malloc(size);
		if (!*load_options) {
			ret = EFI_OUT_OF_RESOURCES;
			goto error;
		}
		memcpy(*load_options, lo.optional_data, size);
		ret = efi_set_load_options(*handle, size, *load_options);
	} else {
		*load_options = NULL;
	}

error:
	free(load_option);

	return ret;
}

/**
 * efi_bootmgr_load() - try to load from BootNext or BootOrder
 *
 * Attempt to load from BootNext or in the order specified by BootOrder
 * EFI variable, the available load-options, finding and returning
 * the first one that can be loaded successfully.
 *
 * @handle:		on return handle for the newly installed image
 * @load_options:	load options set on the loaded image protocol
 * Return:		status code
 */
efi_status_t efi_bootmgr_load(efi_handle_t *handle, void **load_options)
{
	u16 bootnext, *bootorder;
	efi_uintn_t size;
	int i, num;
	efi_status_t ret;

	bs = systab.boottime;
	rs = systab.runtime;

	/* BootNext */
	size = sizeof(bootnext);
	ret = efi_get_variable_int(L"BootNext",
				   &efi_global_variable_guid,
				   NULL, &size, &bootnext, NULL);
	if (ret == EFI_SUCCESS || ret == EFI_BUFFER_TOO_SMALL) {
		/* BootNext does exist here */
		if (ret == EFI_BUFFER_TOO_SMALL || size != sizeof(u16))
			log_err("BootNext must be 16-bit integer\n");

		/* delete BootNext */
		ret = efi_set_variable_int(L"BootNext",
					   &efi_global_variable_guid,
					   0, 0, NULL, false);

		/* load BootNext */
		if (ret == EFI_SUCCESS) {
			if (size == sizeof(u16)) {
				ret = try_load_entry(bootnext, handle,
						     load_options);
				if (ret == EFI_SUCCESS)
					return ret;
				log_warning(
					"Loading from BootNext failed, falling back to BootOrder\n");
			}
		} else {
			log_err("Deleting BootNext failed\n");
		}
	}

	/* BootOrder */
	bootorder = get_var(L"BootOrder", &efi_global_variable_guid, &size);
	if (!bootorder) {
		log_info("BootOrder not defined\n");
		ret = EFI_NOT_FOUND;
		goto error;
	}

	num = size / sizeof(uint16_t);
	for (i = 0; i < num; i++) {
		log_debug("%s trying to load Boot%04X\n", __func__,
			  bootorder[i]);
		ret = try_load_entry(bootorder[i], handle, load_options);
		if (ret == EFI_SUCCESS)
			break;
	}

	free(bootorder);

error:
	return ret;
}