fdt-libcrypto.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * Copyright (c) 2020, Alexandru Gagniuc <mr.nuke.me@gmail.com>
 * Copyright (c) 2013, Google Inc.
 */

#include <libfdt.h>
#include <u-boot/fdt-libcrypto.h>

int fdt_add_bignum(void *blob, int noffset, const char *prop_name,
		   BIGNUM *num, int num_bits)
{
	int nwords = num_bits / 32;
	int size;
	uint32_t *buf, *ptr;
	BIGNUM *tmp, *big2, *big32, *big2_32;
	BN_CTX *ctx;
	int ret;

	tmp = BN_new();
	big2 = BN_new();
	big32 = BN_new();
	big2_32 = BN_new();

	/*
	 * Note: This code assumes that all of the above succeed, or all fail.
	 * In practice memory allocations generally do not fail (unless the
	 * process is killed), so it does not seem worth handling each of these
	 * as a separate case. Technicaly this could leak memory on failure,
	 * but a) it won't happen in practice, and b) it doesn't matter as we
	 * will immediately exit with a failure code.
	 */
	if (!tmp || !big2 || !big32 || !big2_32) {
		fprintf(stderr, "Out of memory (bignum)\n");
		return -ENOMEM;
	}
	ctx = BN_CTX_new();
	if (!ctx) {
		fprintf(stderr, "Out of memory (bignum context)\n");
		return -ENOMEM;
	}
	BN_set_word(big2, 2L);
	BN_set_word(big32, 32L);
	BN_exp(big2_32, big2, big32, ctx); /* B = 2^32 */

	size = nwords * sizeof(uint32_t);
	buf = malloc(size);
	if (!buf) {
		fprintf(stderr, "Out of memory (%d bytes)\n", size);
		return -ENOMEM;
	}

	/* Write out modulus as big endian array of integers */
	for (ptr = buf + nwords - 1; ptr >= buf; ptr--) {
		BN_mod(tmp, num, big2_32, ctx); /* n = N mod B */
		*ptr = cpu_to_fdt32(BN_get_word(tmp));
		BN_rshift(num, num, 32); /*  N = N/B */
	}

	/*
	 * We try signing with successively increasing size values, so this
	 * might fail several times
	 */
	ret = fdt_setprop(blob, noffset, prop_name, buf, size);
	free(buf);
	BN_free(tmp);
	BN_free(big2);
	BN_free(big32);
	BN_free(big2_32);

	return ret ? -FDT_ERR_NOSPACE : 0;
}