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
fdt_add_bignum(void * blob,int noffset,const char * prop_name,BIGNUM * num,int num_bits)10 int 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