common/image.c


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/* SPDX-License-Identifier: GPL-2.0+ */
/*
 * image.c - arm64 kernel Image validation and placement.
 *
 * The relocation rules are the ones from the kernel boot protocol,
 * including the pre a2c1d73b94ed quirks, same math u-boot's
 * booti_setup() runs.
 *
 * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
 */

#include <stdint.h>
#include <string.h>
#include <endian.h>
#include <boot.h>

#define LINUX_ARM64_IMAGE_MAGIC	0x644d5241	/* "ARM\x64" */

#define SZ_16M			0x01000000
#define SZ_2M			0x00200000

/* the 64 byte header from Documentation/arch/arm64/booting.rst */
struct Image_header {
	uint32 code0;		/* executable */
	uint32 code1;		/* unused */
	uint64 text_offset;	/* load offset, LE */
	uint64 image_size;	/* size, LE */
	uint64 flags;		/* bit 3: relocatable */
	uint64 res1;
	uint64 res2;
	uint64 res3;
	uint32 magic;		/* "ARM\x64" */
	uint32 res4;
};

int tb_image_setup(uintptr_t image, struct tb_image *img)
{
	const struct Image_header *ih = (const struct Image_header *)image;
	uint64_t image_size, text_offset;

	if (le32_to_cpu(ih->magic) != LINUX_ARM64_IMAGE_MAGIC)
		return -1;

	if (le64_to_cpu(ih->image_size) == 0) {
		/* ancient image, no size field, assume the old defaults */
		image_size = SZ_16M;
		text_offset = 0x80000;
	} else {
		image_size = le64_to_cpu(ih->image_size);
		text_offset = le64_to_cpu(ih->text_offset);
	}

	/*
	 * flag bit 3 says the image can live anywhere, honour where it
	 * already is. otherwise the base must be 2MB aligned, the
	 * physical offset from there is text_offset.
	 */
	if (le64_to_cpu(ih->flags) & (1ULL << 3)) {
		uintptr_t base = image - text_offset;

		img->load = ((base + SZ_2M - 1) & ~(uintptr_t)(SZ_2M - 1)) +
			    text_offset;
	} else {
		/*
		 * no relocate flag: the image must sit text_offset from a
		 * 2MB aligned base. it is already staged at the fixed
		 * address, treat its own position as the answer.
		 */
		img->load = image;
	}

	/* the whole image, header included, lives at load, entry is code0 */
	img->ep = img->load;
	img->size = image_size;

	return 0;
}