drivers/firmware/efi/efi-bgrt.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright 2012 Intel Corporation
 * Author: Josh Triplett <josh@joshtriplett.org>
 *
 * Based on the bgrt driver:
 * Copyright 2012 Red Hat, Inc <mjg@redhat.com>
 * Author: Matthew Garrett
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/acpi.h>
#include <linux/efi.h>
#include <linux/efi-bgrt.h>

struct acpi_table_bgrt bgrt_tab;
size_t bgrt_image_size;

struct bmp_header {
	u16 id;
	u32 size;
} __packed;

void __init efi_bgrt_init(struct acpi_table_header *table)
{
	void *image;
	struct bmp_header bmp_header;
	struct acpi_table_bgrt *bgrt = &bgrt_tab;

	if (acpi_disabled)
		return;

	if (!efi_enabled(EFI_MEMMAP))
		return;

	if (table->length < sizeof(bgrt_tab)) {
		pr_notice("Ignoring BGRT: invalid length %u (expected %zu)\n",
		       table->length, sizeof(bgrt_tab));
		return;
	}
	*bgrt = *(struct acpi_table_bgrt *)table;
	/*
	 * Only version 1 is defined but some older laptops (seen on Lenovo
	 * Ivy Bridge models) have a correct version 1 BGRT table with the
	 * version set to 0, so we accept version 0 and 1.
	 */
	if (bgrt->version > 1) {
		pr_notice("Ignoring BGRT: invalid version %u (expected 1)\n",
		       bgrt->version);
		goto out;
	}
	if (bgrt->image_type != 0) {
		pr_notice("Ignoring BGRT: invalid image type %u (expected 0)\n",
		       bgrt->image_type);
		goto out;
	}
	if (!bgrt->image_address) {
		pr_notice("Ignoring BGRT: null image address\n");
		goto out;
	}

	if (efi_mem_type(bgrt->image_address) != EFI_BOOT_SERVICES_DATA) {
		pr_notice("Ignoring BGRT: invalid image address\n");
		goto out;
	}
	image = early_memremap(bgrt->image_address, sizeof(bmp_header));
	if (!image) {
		pr_notice("Ignoring BGRT: failed to map image header memory\n");
		goto out;
	}

	memcpy(&bmp_header, image, sizeof(bmp_header));
	early_memunmap(image, sizeof(bmp_header));
	if (bmp_header.id != 0x4d42) {
		pr_notice("Ignoring BGRT: Incorrect BMP magic number 0x%x (expected 0x4d42)\n",
			bmp_header.id);
		goto out;
	}
	bgrt_image_size = bmp_header.size;
	efi_mem_reserve(bgrt->image_address, bgrt_image_size);

	return;
out:
	memset(bgrt, 0, sizeof(bgrt_tab));
}