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. */ 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 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 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 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 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 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 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 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 246 arc4random_buf(void *buf, size_t n) 247 { 248 _ARC4_LOCK(); 249 _rs_random_buf(buf, n); 250 _ARC4_UNLOCK(); 251 } 252