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 <ssp/ssp.h> 39 #include <sys/types.h> 40 #include <sys/time.h> 41 42 #include "libc_private.h" 43 #include "un-namespace.h" 44 45 #define CHACHA_EMBED 46 #define KEYSTREAM_ONLY 47 #if defined(__FreeBSD__) 48 #define ARC4RANDOM_FXRNG 1 49 #else 50 #define ARC4RANDOM_FXRNG 0 51 #endif 52 #include "chacha.c" 53 54 #define minimum(a, b) ((a) < (b) ? (a) : (b)) 55 56 #if defined(__GNUC__) || defined(_MSC_VER) 57 #define inline __inline 58 #else /* __GNUC__ || _MSC_VER */ 59 #define inline 60 #endif /* !__GNUC__ && !_MSC_VER */ 61 62 #define KEYSZ 32 63 #define IVSZ 8 64 #define BLOCKSZ 64 65 #define RSBUFSZ (16*BLOCKSZ) 66 67 #define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */ 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 uint32_t rekey_fuzz = 0; 110 111 #if defined(__FreeBSD__) 112 bool need_init; 113 114 /* 115 * De-couple allocation (which locates the vdso_fxrngp pointer in 116 * auxinfo) from initialization. This allows us to read the root seed 117 * version before we fetch system entropy, maintaining the invariant 118 * that the PRF was seeded with entropy from rs_seed_generation or a 119 * later generation. But never seeded from an earlier generation. 120 * This invariant prevents us from missing a root reseed event. 121 */ 122 need_init = false; 123 if (rs == NULL) { 124 if (_rs_allocate(&rs, &rsx) == -1) 125 abort(); 126 need_init = true; 127 } 128 /* 129 * Transition period: new userspace on old kernel. This should become 130 * a hard error at some point, if the scheme is adopted. 131 */ 132 if (vdso_fxrngp != NULL) 133 rsx->rs_seed_generation = 134 fxrng_load_acq_generation(&vdso_fxrngp->fx_generation32); 135 #endif 136 137 if (getentropy(rnd, sizeof rnd) == -1) 138 _getentropy_fail(); 139 140 #if !defined(__FreeBSD__) 141 if (!rs) 142 _rs_init(rnd, sizeof(rnd)); 143 #else /* __FreeBSD__ */ 144 assert(rs != NULL); 145 if (need_init) 146 _rs_init(rnd, sizeof(rnd)); 147 #endif 148 else 149 _rs_rekey(rnd, sizeof(rnd)); 150 explicit_bzero(rnd, sizeof(rnd)); /* discard source seed */ 151 152 /* invalidate rs_buf */ 153 rs->rs_have = 0; 154 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 155 156 /* rekey interval should not be predictable */ 157 chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz, 158 (uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz)); 159 rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE); 160 } 161 162 static inline void 163 _rs_stir_if_needed(size_t len) 164 { 165 _rs_forkdetect(); 166 if (!rs || rs->rs_count <= len) 167 _rs_stir(); 168 if (rs->rs_count <= len) 169 rs->rs_count = 0; 170 else 171 rs->rs_count -= len; 172 } 173 174 static inline void 175 _rs_rekey(u_char *dat, size_t datlen) 176 { 177 #ifndef KEYSTREAM_ONLY 178 memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf)); 179 #endif 180 /* fill rs_buf with the keystream */ 181 chacha_encrypt_bytes(&rsx->rs_chacha, rsx->rs_buf, 182 rsx->rs_buf, sizeof(rsx->rs_buf)); 183 /* mix in optional user provided data */ 184 if (dat) { 185 size_t i, m; 186 187 m = minimum(datlen, KEYSZ + IVSZ); 188 for (i = 0; i < m; i++) 189 rsx->rs_buf[i] ^= dat[i]; 190 } 191 /* immediately reinit for backtracking resistance */ 192 _rs_init(rsx->rs_buf, KEYSZ + IVSZ); 193 memset(rsx->rs_buf, 0, KEYSZ + IVSZ); 194 rs->rs_have = sizeof(rsx->rs_buf) - KEYSZ - IVSZ; 195 } 196 197 static inline void 198 _rs_random_buf(void *_buf, size_t n) 199 { 200 u_char *buf = (u_char *)_buf; 201 u_char *keystream; 202 size_t m; 203 204 _rs_stir_if_needed(n); 205 while (n > 0) { 206 if (rs->rs_have > 0) { 207 m = minimum(n, rs->rs_have); 208 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) 209 - rs->rs_have; 210 memcpy(buf, keystream, m); 211 memset(keystream, 0, m); 212 buf += m; 213 n -= m; 214 rs->rs_have -= m; 215 } 216 if (rs->rs_have == 0) 217 _rs_rekey(NULL, 0); 218 } 219 } 220 221 static inline void 222 _rs_random_u32(uint32_t *val) 223 { 224 u_char *keystream; 225 226 _rs_stir_if_needed(sizeof(*val)); 227 if (rs->rs_have < sizeof(*val)) 228 _rs_rekey(NULL, 0); 229 keystream = rsx->rs_buf + sizeof(rsx->rs_buf) - rs->rs_have; 230 memcpy(val, keystream, sizeof(*val)); 231 memset(keystream, 0, sizeof(*val)); 232 rs->rs_have -= sizeof(*val); 233 } 234 235 uint32_t 236 arc4random(void) 237 { 238 uint32_t val; 239 240 _ARC4_LOCK(); 241 _rs_random_u32(&val); 242 _ARC4_UNLOCK(); 243 return val; 244 } 245 246 void 247 __ssp_real(arc4random_buf)(void *buf, size_t n) 248 { 249 _ARC4_LOCK(); 250 _rs_random_buf(buf, n); 251 _ARC4_UNLOCK(); 252 } 253