1/*	$OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb Exp $	*/
2
3/*
4 * Copyright (c) 1996, David Mazieres <dm@uun.org>
5 * Copyright (c) 2008, Damien Miller <djm@openbsd.org>
6 * Copyright (c) 2013, Markus Friedl <markus@openbsd.org>
7 * Copyright (c) 2014, Theo de Raadt <deraadt@openbsd.org>
8 *
9 * Permission to use, copy, modify, and distribute this software for any
10 * purpose with or without fee is hereby granted, provided that the above
11 * copyright notice and this permission notice appear in all copies.
12 *
13 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
14 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
15 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
16 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
17 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
18 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
19 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
20 */
21
22/*
23 * ChaCha based random number generator for OpenBSD.
24 */
25
26#include "namespace.h"
27#if defined(__FreeBSD__)
28#include <assert.h>
29#endif
30#include <fcntl.h>
31#include <limits.h>
32#include <pthread.h>
33#include <signal.h>
34#include <stdint.h>
35#include <stdlib.h>
36#include <string.h>
37#include <unistd.h>
38#include <sys/types.h>
39#include <sys/time.h>
40
41#include "libc_private.h"
42#include "un-namespace.h"
43
44#define CHACHA_EMBED
45#define KEYSTREAM_ONLY
46#if defined(__FreeBSD__)
47#define ARC4RANDOM_FXRNG 1
48#else
49#define ARC4RANDOM_FXRNG 0
50#endif
51#include "chacha.c"
52
53#define minimum(a, b) ((a) < (b) ? (a) : (b))
54
55#if defined(__GNUC__) || defined(_MSC_VER)
56#define inline __inline
57#else				/* __GNUC__ || _MSC_VER */
58#define inline
59#endif				/* !__GNUC__ && !_MSC_VER */
60
61#define KEYSZ	32
62#define IVSZ	8
63#define BLOCKSZ	64
64#define RSBUFSZ	(16*BLOCKSZ)
65
66#define REKEY_BASE	(1024*1024) /* NB. should be a power of 2 */
67
68/* Marked INHERIT_ZERO, so zero'd out in fork children. */
69static struct _rs {
70	size_t		rs_have;	/* valid bytes at end of rs_buf */
71	size_t		rs_count;	/* bytes till reseed */
72} *rs;
73
74/* Maybe be preserved in fork children, if _rs_allocate() decides. */
75static struct _rsx {
76	chacha_ctx	rs_chacha;	/* chacha context for random keystream */
77	u_char		rs_buf[RSBUFSZ];	/* keystream blocks */
78#ifdef __FreeBSD__
79	uint32_t	rs_seed_generation;	/* 32-bit userspace RNG version */
80#endif
81} *rsx;
82
83static inline int _rs_allocate(struct _rs **, struct _rsx **);
84static inline void _rs_forkdetect(void);
85#include "arc4random.h"
86
87static inline void _rs_rekey(u_char *dat, size_t datlen);
88
89static inline void
90_rs_init(u_char *buf, size_t n)
91{
92	if (n < KEYSZ + IVSZ)
93		return;
94
95	if (rs == NULL) {
96		if (_rs_allocate(&rs, &rsx) == -1)
97			_exit(1);
98	}
99
100	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8);
101	chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ, NULL);
102}
103
104static void
105_rs_stir(void)
106{
107	u_char rnd[KEYSZ + IVSZ];
108	uint32_t rekey_fuzz = 0;
109
110#if defined(__FreeBSD__)
111	bool need_init;
112
113	/*
114	 * De-couple allocation (which locates the vdso_fxrngp pointer in
115	 * auxinfo) from initialization.  This allows us to read the root seed
116	 * version before we fetch system entropy, maintaining the invariant
117	 * that the PRF was seeded with entropy from rs_seed_generation or a
118	 * later generation.  But never seeded from an earlier generation.
119	 * This invariant prevents us from missing a root reseed event.
120	 */
121	need_init = false;
122	if (rs == NULL) {
123		if (_rs_allocate(&rs, &rsx) == -1)
124			abort();
125		need_init = true;
126	}
127	/*
128	 * Transition period: new userspace on old kernel.  This should become
129	 * a hard error at some point, if the scheme is adopted.
130	 */
131	if (vdso_fxrngp != NULL)
132		rsx->rs_seed_generation =
133		    fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32);
134#endif
135
136	if (getentropy(rnd, sizeof rnd) == -1)
137		_getentropy_fail();
138
139#if !defined(__FreeBSD__)
140	if (!rs)
141		_rs_init(rnd, sizeof(rnd));
142#else /* __FreeBSD__ */
143	assert(rs != NULL);
144	if (need_init)
145		_rs_init(rnd, sizeof(rnd));
146#endif
147	else
148		_rs_rekey(rnd, sizeof(rnd));
149	explicit_bzero(rnd, sizeof(rnd));	/* discard source seed */
150
151	/* invalidate rs_buf */
152	rs->rs_have = 0;
153	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
154
155	/* rekey interval should not be predictable */
156	chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
157	    (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
158	rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
159}
160
161static inline void
162_rs_stir_if_needed(size_t len)
163{
164	_rs_forkdetect();
165	if (!rs || rs->rs_count <= len)
166		_rs_stir();
167	if (rs->rs_count <= len)
168		rs->rs_count = 0;
169	else
170		rs->rs_count -= len;
171}
172
173static inline void
174_rs_rekey(u_char *dat, size_t datlen)
175{
176#ifndef KEYSTREAM_ONLY
177	memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
178#endif
179	/* fill rs_buf with the keystream */
180	chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf,
181	    rsx->rs_buf, sizeof(rsx->rs_buf));
182	/* mix in optional user provided data */
183	if (dat) {
184		size_t i, m;
185
186		m = minimum(datlen, KEYSZ + IVSZ);
187		for (i = 0; i < m; i++)
188			rsx->rs_buf[i] ^= dat[i];
189	}
190	/* immediately reinit for backtracking resistance */
191	_rs_init(rsx->rs_buf, KEYSZ + IVSZ);
192	memset(rsx->rs_buf, 0, KEYSZ + IVSZ);
193	rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ;
194}
195
196static inline void
197_rs_random_buf(void *_buf, size_t n)
198{
199	u_char *buf = (u_char *)_buf;
200	u_char *keystream;
201	size_t m;
202
203	_rs_stir_if_needed(n);
204	while (n > 0) {
205		if (rs->rs_have > 0) {
206			m = minimum(n, rs->rs_have);
207			keystream = rsx->rs_buf + sizeof(rsx->rs_buf)
208			    - rs->rs_have;
209			memcpy(buf, keystream, m);
210			memset(keystream, 0, m);
211			buf += m;
212			n -= m;
213			rs->rs_have -= m;
214		}
215		if (rs->rs_have == 0)
216			_rs_rekey(NULL, 0);
217	}
218}
219
220static inline void
221_rs_random_u32(uint32_t *val)
222{
223	u_char *keystream;
224
225	_rs_stir_if_needed(sizeof(*val));
226	if (rs->rs_have < sizeof(*val))
227		_rs_rekey(NULL, 0);
228	keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have;
229	memcpy(val, keystream, sizeof(*val));
230	memset(keystream, 0, sizeof(*val));
231	rs->rs_have -= sizeof(*val);
232}
233
234uint32_t
235arc4random(void)
236{
237	uint32_t val;
238
239	_ARC4_LOCK();
240	_rs_random_u32(&val);
241	_ARC4_UNLOCK();
242	return val;
243}
244
245void
246arc4random_buf(void *buf, size_t n)
247{
248	_ARC4_LOCK();
249	_rs_random_buf(buf, n);
250	_ARC4_UNLOCK();
251}
252