1 /* $OpenBSD: arc4random.c,v 1.55 2019/03/24 17:56:54 deraadt 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 <sys/cdefs.h> 27 __FBSDID("$FreeBSD$"); 28 29 #include "namespace.h" 30 #if defined(__FreeBSD__) 31 #include <assert.h> 32 #endif 33 #include <fcntl.h> 34 #include <limits.h> 35 #include <pthread.h> 36 #include <signal.h> 37 #include <stdint.h> 38 #include <stdlib.h> 39 #include <string.h> 40 #include <unistd.h> 41 #include <sys/types.h> 42 #include <sys/time.h> 43 44 #include "libc_private.h" 45 #include "un-namespace.h" 46 47 #define CHACHA_EMBED 48 #define KEYSTREAM_ONLY 49 #if defined(__FreeBSD__) 50 #define ARC4RANDOM_FXRNG 1 51 #else 52 #define ARC4RANDOM_FXRNG 0 53 #endif 54 #include "chacha.c" 55 56 #define minimum(a, b) ((a) < (b) ? (a) : (b)) 57 58 #if defined(__GNUC__) || defined(_MSC_VER) 59 #define inline __inline 60 #else /* __GNUC__ || _MSC_VER */ 61 #define inline 62 #endif /* !__GNUC__ && !_MSC_VER */ 63 64 #define KEYSZ 32 65 #define IVSZ 8 66 #define BLOCKSZ 64 67 #define RSBUFSZ (16*BLOCKSZ) 68 69 /* Marked INHERIT_ZERO, so zero'd out in fork children. */ 70 static struct _rs { 71 size_t rs_have; /* valid bytes at end of rs_buf */ 72 size_t rs_count; /* bytes till reseed */ 73 } *rs; 74 75 /* Maybe be preserved in fork children, if _rs_allocate() decides. */ 76 static struct _rsx { 77 chacha_ctx rs_chacha; /* chacha context for random keystream */ 78 u_char rs_buf[RSBUFSZ]; /* keystream blocks */ 79 #ifdef __FreeBSD__ 80 uint32_t rs_seed_generation; /* 32-bit userspace RNG version */ 81 #endif 82 } *rsx; 83 84 static inline int _rs_allocate(struct _rs **, struct _rsx **); 85 static inline void _rs_forkdetect(void); 86 #include "arc4random.h" 87 88 static inline void _rs_rekey(u_char *dat, size_t datlen); 89 90 static inline void 91 _rs_init(u_char *buf, size_t n) 92 { 93 if (n < KEYSZ + IVSZ) 94 return; 95 96 if (rs == NULL) { 97 if (_rs_allocate(&rs, &rsx) == -1) 98 _exit(1); 99 } 100 101 chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8); 102 chacha_ivsetup(&rsx->rs_chacha, buf + KEYSZ, NULL); 103 } 104 105 static void 106 _rs_stir(void) 107 { 108 u_char rnd[KEYSZ + IVSZ]; 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 rs->rs_count = 1600000; 156 } 157 158 static inline void 159 _rs_stir_if_needed(size_t len) 160 { 161 _rs_forkdetect(); 162 if (!rs || rs->rs_count <= len) 163 _rs_stir(); 164 if (rs->rs_count <= len) 165 rs->rs_count = 0; 166 else 167 rs->rs_count -= len; 168 } 169 170 static inline void 171 _rs_rekey(u_char *dat, size_t datlen) 172 { 173 #ifndef KEYSTREAM_ONLY 174 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 175 #endif 176 /* fill rs_buf with the keystream */ 177 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 178 rsx->rs_buf, sizeof(rsx->rs_buf)); 179 /* mix in optional user provided data */ 180 if (dat) { 181 size_t i, m; 182 183 m = minimum(datlen, KEYSZ + IVSZ); 184 for (i = 0; i < m; i++) 185 rsx->rs_buf[i] ^= dat[i]; 186 } 187 /* immediately reinit for backtracking resistance */ 188 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 189 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 190 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 191 } 192 193 static inline void 194 _rs_random_buf(void *_buf, size_t n) 195 { 196 u_char *buf = (u_char *)_buf; 197 u_char *keystream; 198 size_t m; 199 200 _rs_stir_if_needed(n); 201 while (n > 0) { 202 if (rs->rs_have > 0) { 203 m = minimum(n, rs->rs_have); 204 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 205 - rs->rs_have; 206 memcpy(buf, keystream, m); 207 memset(keystream, 0, m); 208 buf += m; 209 n -= m; 210 rs->rs_have -= m; 211 } 212 if (rs->rs_have == 0) 213 _rs_rekey(NULL, 0); 214 } 215 } 216 217 static inline void 218 _rs_random_u32(uint32_t *val) 219 { 220 u_char *keystream; 221 222 _rs_stir_if_needed(sizeof(*val)); 223 if (rs->rs_have < sizeof(*val)) 224 _rs_rekey(NULL, 0); 225 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 226 memcpy(val, keystream, sizeof(*val)); 227 memset(keystream, 0, sizeof(*val)); 228 rs->rs_have -= sizeof(*val); 229 } 230 231 uint32_t 232 arc4random(void) 233 { 234 uint32_t val; 235 236 _ARC4_LOCK(); 237 _rs_random_u32(&val); 238 _ARC4_UNLOCK(); 239 return val; 240 } 241 242 void 243 arc4random_buf(void *buf, size_t n) 244 { 245 _ARC4_LOCK(); 246 _rs_random_buf(buf, n); 247 _ARC4_UNLOCK(); 248 } 249