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 fallback where image_size is 0 and
 * the offset was fixed. qemu virt loads us at the bottom of RAM, same
 * place the kernel wants to be, so the common case is a no move.
 *
 * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
 */

#include <string.h>
#include <sys/types.h>
#include <stdint.h>
#include <boot.h>
#include <endian.h>

#define SZ_2M		0x200000UL
#define SZ_16M		0x1000000UL
#define IMAGE_OFFSET_FIXUP	0x80000ULL

int tb_image_setup(uintptr_t image, uintptr_t mem_base, uint32 mem_size,
		   struct tb_image *img)
{
	struct Image_header *ih = (struct Image_header *)image;
	uint64_t image_size;
	uint64_t text_offset;
	uintptr_t dst;

	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 = IMAGE_OFFSET_FIXUP;
	} else {
		image_size = le64_to_cpu(ih->image_size);
		text_offset = le64_to_cpu(ih->text_offset);
	}

	if (image_size > mem_size)
		return -1;

	/*
	 * 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))
		dst = image - text_offset;
	else
		dst = mem_base;

	/* the whole image, header included, sits here, and code0 at its
	 * start is the first instruction executed */
	img->load = ((dst + SZ_2M - 1) & ~(uintptr_t)(SZ_2M - 1)) + text_offset;
	img->ep = img->load;
	img->size = image_size;

	if (dst + image_size > mem_base + mem_size)
		return -1;

	return 0;
}