1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Copyright (c) 2020, Alexandru Gagniuc <mr.nuke.me@gmail.com>
4 * Copyright (c) 2013, Google Inc.
5 */
6
7#include <libfdt.h>
8#include <u-boot/fdt-libcrypto.h>
9
10int fdt_add_bignum(void *blob, int noffset, const char *prop_name,
11		   BIGNUM *num, int num_bits)
12{
13	int nwords = num_bits / 32;
14	int size;
15	uint32_t *buf, *ptr;
16	BIGNUM *tmp, *big2, *big32, *big2_32;
17	BN_CTX *ctx;
18	int ret;
19
20	tmp = BN_new();
21	big2 = BN_new();
22	big32 = BN_new();
23	big2_32 = BN_new();
24
25	/*
26	 * Note: This code assumes that all of the above succeed, or all fail.
27	 * In practice memory allocations generally do not fail (unless the
28	 * process is killed), so it does not seem worth handling each of these
29	 * as a separate case. Technicaly this could leak memory on failure,
30	 * but a) it won't happen in practice, and b) it doesn't matter as we
31	 * will immediately exit with a failure code.
32	 */
33	if (!tmp || !big2 || !big32 || !big2_32) {
34		fprintf(stderr, "Out of memory (bignum)\n");
35		return -ENOMEM;
36	}
37	ctx = BN_CTX_new();
38	if (!ctx) {
39		fprintf(stderr, "Out of memory (bignum context)\n");
40		return -ENOMEM;
41	}
42	BN_set_word(big2, 2L);
43	BN_set_word(big32, 32L);
44	BN_exp(big2_32, big2, big32, ctx); /* B = 2^32 */
45
46	size = nwords * sizeof(uint32_t);
47	buf = malloc(size);
48	if (!buf) {
49		fprintf(stderr, "Out of memory (%d bytes)\n", size);
50		return -ENOMEM;
51	}
52
53	/* Write out modulus as big endian array of integers */
54	for (ptr = buf + nwords - 1; ptr >= buf; ptr--) {
55		BN_mod(tmp, num, big2_32, ctx); /* n = N mod B */
56		*ptr = cpu_to_fdt32(BN_get_word(tmp));
57		BN_rshift(num, num, 32); /*  N = N/B */
58	}
59
60	/*
61	 * We try signing with successively increasing size values, so this
62	 * might fail several times
63	 */
64	ret = fdt_setprop(blob, noffset, prop_name, buf, size);
65	free(buf);
66	BN_free(tmp);
67	BN_free(big2);
68	BN_free(big32);
69	BN_free(big2_32);
70
71	return ret ? -FDT_ERR_NOSPACE : 0;
72}
73