sys/kern/subr_csprng.c

   1 /*
   2  * Copyright (c) 2014 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Alex Hornung <alex@alexhornung.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34 #include <sys/param.h>
  35 #include <sys/systm.h>
  36 #include <sys/kernel.h>
  37 #include <sys/spinlock.h>
  38 #include <sys/spinlock2.h>
  39 #include <sys/csprng.h>
  40
  41 /*
  42  * Minimum amount of bytes in pool before we consider it
  43  * good enough.
  44  * It's 64 + the hash digest size because we always
  45  * reinitialize the pools with a hash of the previous chunk
  46  * of entropy.
  47  */
  48 #define MIN_POOL_SIZE   64 + SHA256_DIGEST_LENGTH
  49
  50 /* Minimum reseed interval */
  51 #define MIN_RESEED_INTERVAL     hz/10
  52
  53 /* Lock macros */
  54 #define POOL_LOCK_INIT(pool) \
  55     spin_init(&(pool)->lock, "csprng_poollock")
  56
  57 #define POOL_LOCK(pool)      \
  58     spin_lock(&pool->lock)
  59
  60 #define POOL_TRYLOCK(pool)   \
  61     spin_trylock(&pool->lock)
  62
  63 #define POOL_UNLOCK(pool)    \
  64     spin_unlock(&pool->lock)
  65
  66
  67 #define STATE_LOCK_INIT(state)  \
  68     spin_init(&state->lock, "csprng_statelock")
  69
  70 #define STATE_LOCK(state)       \
  71     spin_lock(&state->lock)
  72
  73 #define STATE_UNLOCK(state)     \
  74     spin_unlock(&state->lock)
  75
  76 #define STATE_SLEEP(state, wmesg, timo) \
  77     ssleep(state, &state->lock, 0, wmesg, timo)
  78
  79 #define STATE_WAKEUP(state)     \
  80     wakeup(state)
  81
  82 static void csprng_reseed_callout(void *arg);
  83 static int csprng_reseed(struct csprng_state *state);
  84
  85 static struct timeval csprng_reseed_interval = { 0, 100000 };
  86
  87 static
  88 int
  89 csprng_pool_init(struct csprng_pool *pool, uint8_t *buf, size_t len)
  90 {
  91         pool->bytes = 0;
  92         SHA256_Init(&pool->hash_ctx);
  93
  94         if (len > 0)
  95                 SHA256_Update(&pool->hash_ctx, buf, len);
  96
  97         return 0;
  98 }
  99
 100 int
 101 csprng_init(struct csprng_state *state)
 102 {
 103         int i, r;
 104
 105         bzero(state->key, sizeof(state->key));
 106         bzero(&state->cipher_ctx, sizeof(state->cipher_ctx));
 107         bzero(state->src_pool_idx, sizeof(state->src_pool_idx));
 108         bzero(&state->last_reseed, sizeof(state->last_reseed));
 109
 110         state->nonce = 0;
 111         state->ctr   = 0;
 112         state->reseed_cnt = 0;
 113         state->failed_reseeds = 0;
 114         state->callout_based_reseed = 0;
 115
 116         STATE_LOCK_INIT(state);
 117
 118         for (i = 0; i < 32; i++) {
 119                 r = csprng_pool_init(&state->pool[i], NULL, 0);
 120                 if (r != 0)
 121                         break;
 122                 POOL_LOCK_INIT(&state->pool[i]);
 123         }
 124
 125         return r;
 126 }
 127
 128 int
 129 csprng_init_reseed(struct csprng_state *state)
 130 {
 131         state->callout_based_reseed = 1;
 132
 133         callout_init_mp(&state->reseed_callout);
 134         callout_reset(&state->reseed_callout, MIN_RESEED_INTERVAL,
 135             csprng_reseed_callout, state);
 136
 137         return 0;
 138 }
 139
 140 /*
 141  * XXX:
 142  * Sources don't really a uniquely-allocated src id...
 143  * another way we could do that is by simply using
 144  * (uint8_t)__LINE__ as the source id... cheap & cheerful.
 145  */
 146
 147 static
 148 int
 149 encrypt_bytes(struct csprng_state *state, uint8_t *out, uint8_t *in, size_t bytes)
 150 {
 151         /* Update nonce whenever the counter is about to overflow */
 152         if (chacha_check_counter(&state->cipher_ctx)) {
 153                 ++state->nonce;
 154                 chacha_ivsetup(&state->cipher_ctx, (const uint8_t *)&state->nonce);
 155         }
 156
 157         chacha_encrypt_bytes(&state->cipher_ctx, in, out, (uint32_t)bytes);
 158
 159         return 0;
 160 }
 161
 162 /*
 163  * XXX: flags is currently unused, but could be used to know whether
 164  *      it's a /dev/random or /dev/urandom read, and make sure that
 165  *      enough entropy has been collected recently, etc.
 166  */
 167 int
 168 csprng_get_random(struct csprng_state *state, uint8_t *out, int bytes,
 169     int flags __unused)
 170 {
 171         int cnt;
 172         int total_bytes = 0;
 173
 174         /*
 175          * XXX: can optimize a bit by digging into chacha_encrypt_bytes
 176          *      and removing the xor of the stream with the input - that
 177          *      way we don't have to xor the output (which we provide
 178          *      as input).
 179          */
 180         bzero(out, bytes);
 181
 182         STATE_LOCK(state);
 183
 184 again:
 185         if (!state->callout_based_reseed &&
 186              ratecheck(&state->last_reseed, &csprng_reseed_interval)) {
 187                 csprng_reseed(state);
 188         }
 189
 190         /*
 191          * If no reseed has occurred yet, we can't possibly give out
 192          * any random data.
 193          * Sleep until entropy is added to the pools (or a callout-based
 194          * reseed, if enabled, occurs).
 195          */
 196         if (state->reseed_cnt == 0) {
 197                 STATE_SLEEP(state, "csprngrsd", 0);
 198                 goto again;
 199         }
 200
 201         while (bytes > 0) {
 202                 /* Limit amount of output without rekeying to 2^20 */
 203                 cnt = (bytes > (1 << 20)) ? (1 << 20) : bytes;
 204
 205                 encrypt_bytes(state, out, out, cnt);
 206
 207                 /* Update key and rekey cipher */
 208                 encrypt_bytes(state, state->key, state->key, sizeof(state->key));
 209                 chacha_keysetup(&state->cipher_ctx, state->key,
 210                     8*sizeof(state->key));
 211
 212                 out += cnt;
 213                 bytes -= cnt;
 214                 total_bytes += cnt;
 215         }
 216
 217         STATE_UNLOCK(state);
 218
 219         return total_bytes;
 220 }
 221
 222 static
 223 int
 224 csprng_reseed(struct csprng_state *state)
 225 {
 226         int i;
 227         struct csprng_pool *pool;
 228         SHA256_CTX hash_ctx;
 229         uint8_t digest[SHA256_DIGEST_LENGTH];
 230
 231         /*
 232          * If there's not enough entropy in the first
 233          * pool, don't reseed.
 234          */
 235         if (state->pool[0].bytes < MIN_POOL_SIZE) {
 236                 ++state->failed_reseeds;
 237                 return 1;
 238         }
 239
 240         SHA256_Init(&hash_ctx);
 241
 242         /*
 243          * Update hash that will result in new key with the
 244          * old key.
 245          */
 246         SHA256_Update(&hash_ctx, state->key, sizeof(state->key));
 247
 248         state->reseed_cnt++;
 249
 250         for (i = 0; i < 32; i++) {
 251                 if ((state->reseed_cnt % (1 << i)) != 0)
 252                         break;
 253
 254                 pool = &state->pool[i];
 255                 POOL_LOCK(pool);
 256
 257                 /*
 258                  * Finalize hash of the entropy in this pool.
 259                  */
 260                 SHA256_Final(digest, &pool->hash_ctx);
 261
 262                 /*
 263                  * Reinitialize pool with a hash of the old pool digest.
 264                  * This is a slight deviation from Fortuna as per reference,
 265                  * but is in line with other Fortuna implementations.
 266                  */
 267                 csprng_pool_init(pool, digest, sizeof(digest));
 268
 269                 POOL_UNLOCK(pool);
 270
 271                 /*
 272                  * Update hash that will result in new key with this
 273                  * pool's hashed entropy.
 274                  */
 275                 SHA256_Update(&hash_ctx, digest, sizeof(digest));
 276         }
 277
 278         SHA256_Final(state->key, &hash_ctx);
 279
 280         /* Update key and rekey cipher */
 281         chacha_keysetup(&state->cipher_ctx, state->key,
 282             8*sizeof(state->key));
 283
 284         /* Increment the nonce if the counter overflows */
 285         if (chacha_incr_counter(&state->cipher_ctx)) {
 286                 ++state->nonce;
 287                 chacha_ivsetup(&state->cipher_ctx, (const uint8_t *)&state->nonce);
 288         }
 289
 290         return 0;
 291 }
 292
 293 static
 294 void
 295 csprng_reseed_callout(void *arg)
 296 {
 297         struct csprng_state *state = (struct csprng_state *)arg;
 298         int reseed_interval = MIN_RESEED_INTERVAL;
 299
 300         STATE_LOCK(state);
 301
 302         csprng_reseed(arg);
 303
 304         STATE_WAKEUP(state);
 305         STATE_UNLOCK(state);
 306
 307         callout_reset(&state->reseed_callout, reseed_interval,
 308             csprng_reseed_callout, state);
 309 }
 310
 311 int
 312 csprng_add_entropy(struct csprng_state *state, int src_id,
 313     const uint8_t *entropy, size_t bytes, int flags)
 314 {
 315         struct csprng_pool *pool;
 316         int pool_id;
 317
 318         /*
 319          * Pick the next pool for this source on a round-robin
 320          * basis.
 321          */
 322         src_id &= 0xff;
 323         pool_id = state->src_pool_idx[src_id]++ & 0x1f;
 324         pool = &state->pool[pool_id];
 325
 326         if (flags & CSPRNG_TRYLOCK) {
 327                 /*
 328                  * If we are asked to just try the lock instead
 329                  * of spinning until we get it, return if we
 330                  * can't get a hold of the lock right now.
 331                  */
 332                 if (!POOL_TRYLOCK(pool))
 333                         return -1;
 334         } else {
 335                 POOL_LOCK(pool);
 336         }
 337
 338         SHA256_Update(&pool->hash_ctx, (const uint8_t *)&src_id, sizeof(src_id));
 339         SHA256_Update(&pool->hash_ctx, (const uint8_t *)&bytes, sizeof(bytes));
 340         SHA256_Update(&pool->hash_ctx, entropy, bytes);
 341
 342         pool->bytes += bytes;
 343
 344         POOL_UNLOCK(pool);
 345
 346         /*
 347          * If a wakeup is missed, it doesn't matter too much - it'll get woken
 348          * up by the next add_entropy() call.
 349          */
 350         STATE_WAKEUP(state);
 351
 352         return 0;
 353 }