lib/libc/gen/arc4random.c

   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 <sys/cdefs.h>
  27 #include "namespace.h"
  28 #if defined(__FreeBSD__)
  29 #include <assert.h>
  30 #endif
  31 #include <fcntl.h>
  32 #include <limits.h>
  33 #include <pthread.h>
  34 #include <signal.h>
  35 #include <stdint.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <unistd.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 arc4random_buf(void *buf, size_t n)
 248 {
 249         _ARC4_LOCK();
 250         _rs_random_buf(buf, n);
 251         _ARC4_UNLOCK();
 252 }