common/zircon_util.c

/*
 * Copyright (c) 2020 The Fuchsia Authors
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <common.h>
#include <emmc_storage.h>
#include <mmc.h>
#include <u-boot/sha256.h>
#include <zircon_util.h>

#define SHA256_DIGEST_SIZE 32

/*
 * Generate a default serial number of given size (including null terminator)
 * based on the eMMC device info.
 */
int get_default_serial_number(char *sn, size_t size)
{
	if ((sn == NULL) || !size) {
		return -1;
	}

	// Get eMMC device info.
	struct mmc *mmc = find_mmc_device(STORAGE_DEV_EMMC);
	if (!mmc) {
		printf("Cannot find eMMC dev.\n");
		return -1;
	}

	// The eMMC CID contains a serial number. Hash it to get a default serial number for use
	// in case a real one isn't available.
	uint8_t hash[SHA256_DIGEST_SIZE];
	sha256_csum_wd((const uchar*)mmc->cid, sizeof mmc->cid, hash, CHUNKSZ_SHA256);

	int i = SHA256_DIGEST_SIZE - 1;
	/* if |sn| is too small to fit all hash digest, calc how many can be stored */
	if (size < (SHA256_DIGEST_SIZE * 2 + 1)) {
		i = ((size - 1) / 2) - 1;
	}

	static const char hex[] = "0123456789ABCDEF";
	int j = 0;
	for (; i >= 0; i--) {
		sn[j++] = hex[(hash[i] >> 4) & 0xF];
		sn[j++] = hex[hash[i] & 0xF];
	}
	sn[size - 1] = '\0';

	return 0;
}