util/cbfstool/platform_fixups.c

/* SPDX-License-Identifier: GPL-2.0-only */

#include "cbfs.h"
#include "cbfs_sections.h"
#include "elfparsing.h"

/*
 * NOTE: This currently only implements support for MBN version 6 (as used by sc7180). Support
 * for other MBN versions could probably be added but may require more parsing to tell them
 * apart, and minor modifications (e.g. different hash algorithm). Add later as needed.
 */
static void *qualcomm_find_hash(struct buffer *in, size_t bb_offset, struct vb2_hash *real_hash)
{
	struct buffer elf;
	buffer_clone(&elf, in);

	/* When buffer_size(&elf) becomes this small, we know we've searched through 32KiB (or
	   the whole bootblock) without finding anything, so we know we can stop looking. */
	size_t search_end_size = MIN(0, buffer_size(in) - 32 * KiB);

	/* To identify a Qualcomm image, first we find the GPT header... */
	while (buffer_size(&elf) > search_end_size &&
	       !buffer_check_magic(&elf, "EFI PART", 8))
		buffer_seek(&elf, 512);

	/* ...then shortly afterwards there's an ELF header... */
	while (buffer_size(&elf) > search_end_size &&
	       !buffer_check_magic(&elf, ELFMAG, 4))
		buffer_seek(&elf, 512);

	if (buffer_size(&elf) <= search_end_size)
		return NULL;	/* Doesn't seem to be a Qualcomm image. */

	struct parsed_elf pelf;
	if (parse_elf(&elf, &pelf, ELF_PARSE_PHDR))
		return NULL;	/* Not an ELF -- guess not a Qualcomm MBN after all? */

	/* Qualcomm stores an array of SHA-384 hashes in a special ELF segment. One special one
	   to start with, and then one for each segment in order. */
	void *bb_hash = NULL;
	void *hashtable = NULL;
	int i;
	int bb_segment = -1;
	for (i = 0; i < pelf.ehdr.e_phnum; i++) {
		Elf64_Phdr *ph = &pelf.phdr[i];
		if ((ph->p_flags & PF_QC_SG_MASK) == PF_QC_SG_HASH) {
			if ((int)ph->p_filesz !=
			    (pelf.ehdr.e_phnum + 1) * VB2_SHA384_DIGEST_SIZE) {
				ERROR("fixups: Qualcomm hash segment has wrong size!\n");
				goto destroy_elf;
			} /* Found the table with the hashes -- store its address. */
			hashtable = buffer_get(&elf) + ph->p_offset;
		} else if (bb_segment < 0 && ph->p_offset + ph->p_filesz < buffer_size(&elf) &&
			   buffer_offset(&elf) + ph->p_offset <= bb_offset &&
			   buffer_offset(&elf) + ph->p_offset + ph->p_filesz > bb_offset) {
			bb_segment = i;	/* Found the bootblock segment -- store its index. */
		}
	}
	if (!hashtable)	/* ELF but no special QC hash segment -- guess not QC after all? */
		goto destroy_elf;
	if (bb_segment < 0) {	/* Can assume it's QC if we found the special segment. */
		ERROR("fixups: Cannot find bootblock code in Qualcomm MBN!\n");
		goto destroy_elf;
	}

	/* Pass out the actual hash of the current bootblock segment in |real_hash|. */
	if (vb2_hash_calculate(buffer_get(&elf) + pelf.phdr[bb_segment].p_offset,
			       pelf.phdr[bb_segment].p_filesz, VB2_HASH_SHA384, real_hash)) {
		ERROR("fixups: vboot digest error\n");
		goto destroy_elf;
	} /* Return pointer to where the bootblock hash needs to go in Qualcomm's table. */
	bb_hash = hashtable + (bb_segment + 1) * VB2_SHA384_DIGEST_SIZE;

destroy_elf:
	parsed_elf_destroy(&pelf);
	return bb_hash;
}

static bool qualcomm_probe(struct buffer *buffer, size_t offset)
{
	struct vb2_hash real_hash;
	void *table_hash = qualcomm_find_hash(buffer, offset, &real_hash);
	if (!table_hash)
		return false;

	if (memcmp(real_hash.raw, table_hash, VB2_SHA384_DIGEST_SIZE)) {
		ERROR("fixups: Identified Qualcomm MBN, but existing hash doesn't match!\n");
		return false;
	}

	return true;
}

static int qualcomm_fixup(struct buffer *buffer, size_t offset)
{
	struct vb2_hash real_hash;
	void *table_hash = qualcomm_find_hash(buffer, offset, &real_hash);
	if (!table_hash) {
		ERROR("fixups: Cannot find Qualcomm MBN headers anymore!\n");
		return -1;
	}

	memcpy(table_hash, real_hash.raw, VB2_SHA384_DIGEST_SIZE);
	INFO("fixups: Updated Qualcomm MBN header bootblock hash.\n");
	return 0;
}

platform_fixup_func platform_fixups_probe(struct buffer *buffer, size_t offset,
					  const char *region_name)
{
	if (!strcmp(region_name, SECTION_NAME_BOOTBLOCK)) {
		if (qualcomm_probe(buffer, offset))
			return qualcomm_fixup;
	} else if (!strcmp(region_name, SECTION_NAME_PRIMARY_CBFS)) {
		/* TODO: add fixups for primary CBFS bootblock platforms, if needed */
	} else {
		ERROR("%s called for unexpected FMAP region %s!\n", __func__, region_name);
	}

	return NULL;
}