1 /* $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb Exp $ */
2
3 /*
4 * Copyright (c) 1996, David Mazieres <[email protected]>
5 * Copyright (c) 2008, Damien Miller <[email protected]>
6 * Copyright (c) 2013, Markus Friedl <[email protected]>
7 * Copyright (c) 2014, Theo de Raadt <[email protected]>
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. */
69 static 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. */
75 static 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
83 static inline int _rs_allocate(struct _rs **, struct _rsx **);
84 static inline void _rs_forkdetect(void);
85 #include "arc4random.h"
86
87 static inline void _rs_rekey(u_char *dat, size_t datlen);
88
89 static inline void
_rs_init(u_char * buf,size_t n)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
104 static void
_rs_stir(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
161 static inline void
_rs_stir_if_needed(size_t len)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
173 static inline void
_rs_rekey(u_char * dat,size_t datlen)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
196 static inline void
_rs_random_buf(void * _buf,size_t n)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
220 static inline void
_rs_random_u32(uint32_t * val)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
234 uint32_t
arc4random(void)235 arc4random(void)
236 {
237 uint32_t val;
238
239 _ARC4_LOCK();
240 _rs_random_u32(&val);
241 _ARC4_UNLOCK();
242 return val;
243 }
244
245 void
arc4random_buf(void * buf,size_t n)246 arc4random_buf(void *buf, size_t n)
247 {
248 _ARC4_LOCK();
249 _rs_random_buf(buf, n);
250 _ARC4_UNLOCK();
251 }
252