arc4random.c

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    1 /*-
    2  * Copyright (c) 2017 The FreeBSD Foundation
    3  *
    4  * Redistribution and use in source and binary forms, with or without
    5  * modification, are permitted provided that the following conditions
    6  * are met:
    7  * 1. Redistributions of source code must retain the above copyright
    8  *    notice, this list of conditions and the following disclaimer
    9  *    in this position and unchanged.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   24  *
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD$");
   29 
   30 #include <sys/types.h>
   31 #include <sys/param.h>
   32 #include <sys/kernel.h>
   33 #include <sys/libkern.h>
   34 #include <sys/linker.h>
   35 #include <sys/lock.h>
   36 #include <sys/malloc.h>
   37 #include <sys/msan.h>
   38 #include <sys/mutex.h>
   39 #include <sys/random.h>
   40 #include <sys/smp.h>
   41 #include <sys/time.h>
   42 
   43 #include <machine/cpu.h>
   44 
   45 #include <crypto/chacha20/chacha.h>
   46 #include <crypto/sha2/sha256.h>
   47 #include <dev/random/randomdev.h>
   48 #ifdef RANDOM_FENESTRASX
   49 #include <dev/random/fenestrasX/fx_pub.h>
   50 #endif
   51 
   52 #define CHACHA20_RESEED_BYTES   65536
   53 #define CHACHA20_RESEED_SECONDS 300
   54 #define CHACHA20_KEYBYTES       32
   55 #define CHACHA20_BUFFER_SIZE    64
   56 
   57 CTASSERT(CHACHA20_KEYBYTES*8 >= CHACHA_MINKEYLEN);
   58 
   59 #ifndef RANDOM_FENESTRASX
   60 int arc4rand_iniseed_state = ARC4_ENTR_NONE;
   61 #endif
   62 
   63 MALLOC_DEFINE(M_CHACHA20RANDOM, "chacha20random", "chacha20random structures");
   64 
   65 struct chacha20_s {
   66         struct mtx mtx;
   67         int numbytes;
   68         time_t t_reseed;
   69         uint8_t m_buffer[CHACHA20_BUFFER_SIZE];
   70         struct chacha_ctx ctx;
   71 #ifdef RANDOM_FENESTRASX
   72         uint64_t seed_version;
   73 #endif
   74 } __aligned(CACHE_LINE_SIZE);
   75 
   76 static struct chacha20_s *chacha20inst = NULL;
   77 
   78 #define CHACHA20_FOREACH(_chacha20) \
   79         for (_chacha20 = &chacha20inst[0]; \
   80              _chacha20 <= &chacha20inst[mp_maxid]; \
   81              _chacha20++)
   82 
   83 /*
   84  * Mix up the current context.
   85  */
   86 static void
   87 chacha20_randomstir(struct chacha20_s *chacha20)
   88 {
   89         struct timeval tv_now;
   90         uint8_t key[CHACHA20_KEYBYTES];
   91 #ifdef RANDOM_FENESTRASX
   92         uint64_t seed_version;
   93 
   94 #else
   95         if (__predict_false(random_bypass_before_seeding && !is_random_seeded())) {
   96                 SHA256_CTX ctx;
   97                 uint64_t cc;
   98                 uint32_t fver;
   99 
  100                 if (!arc4random_bypassed_before_seeding) {
  101                         arc4random_bypassed_before_seeding = true;
  102                         if (!random_bypass_disable_warnings)
  103                                 printf("arc4random: WARNING: initial seeding "
  104                                     "bypassed the cryptographic random device "
  105                                     "because it was not yet seeded and the "
  106                                     "knob 'bypass_before_seeding' was "
  107                                     "enabled.\n");
  108                 }
  109 
  110                 /*
  111                  * "key" is intentionally left uninitialized here, so with KMSAN
  112                  * enabled the arc4random() return value may be marked
  113                  * uninitialized, leading to spurious reports.  Lie to KMSAN to
  114                  * avoid this situation.
  115                  */
  116                 kmsan_mark(key, sizeof(key), KMSAN_STATE_INITED);
  117 
  118                 /* Last ditch effort to inject something in a bad condition. */
  119                 cc = get_cyclecount();
  120                 SHA256_Init(&ctx);
  121                 SHA256_Update(&ctx, key, sizeof(key));
  122                 SHA256_Update(&ctx, &cc, sizeof(cc));
  123                 fver = __FreeBSD_version;
  124                 SHA256_Update(&ctx, &fver, sizeof(fver));
  125                 _Static_assert(sizeof(key) == SHA256_DIGEST_LENGTH,
  126                     "make sure 256 bits is still 256 bits");
  127                 SHA256_Final(key, &ctx);
  128         } else {
  129 #endif
  130 #ifdef RANDOM_FENESTRASX
  131                 read_random_key(key, CHACHA20_KEYBYTES, &seed_version);
  132 #else
  133                 /*
  134                 * If the loader(8) did not have an entropy stash from the
  135                 * previous shutdown to load, then we will block.  The answer is
  136                 * to make sure there is an entropy stash at shutdown time.
  137                 *
  138                 * On the other hand, if the random_bypass_before_seeding knob
  139                 * was set and we landed in this branch, we know this won't
  140                 * block because we know the random device is seeded.
  141                 */
  142                 read_random(key, CHACHA20_KEYBYTES);
  143         }
  144 #endif
  145         getmicrouptime(&tv_now);
  146         mtx_lock(&chacha20->mtx);
  147         chacha_keysetup(&chacha20->ctx, key, CHACHA20_KEYBYTES*8);
  148         chacha_ivsetup(&chacha20->ctx, (u_char *)&tv_now.tv_sec, (u_char *)&tv_now.tv_usec);
  149         /* Reset for next reseed cycle. */
  150         chacha20->t_reseed = tv_now.tv_sec + CHACHA20_RESEED_SECONDS;
  151         chacha20->numbytes = 0;
  152 #ifdef RANDOM_FENESTRASX
  153         chacha20->seed_version = seed_version;
  154 #endif
  155         mtx_unlock(&chacha20->mtx);
  156 }
  157 
  158 /*
  159  * Initialize the contexts.
  160  */
  161 static void
  162 chacha20_init(void)
  163 {
  164         struct chacha20_s *chacha20;
  165 
  166         chacha20inst = malloc((mp_maxid + 1) * sizeof(struct chacha20_s),
  167                         M_CHACHA20RANDOM, M_NOWAIT | M_ZERO);
  168         KASSERT(chacha20inst != NULL, ("chacha20_init: memory allocation error"));
  169 
  170         CHACHA20_FOREACH(chacha20) {
  171                 mtx_init(&chacha20->mtx, "chacha20_mtx", NULL, MTX_DEF);
  172                 chacha20->t_reseed = -1;
  173                 chacha20->numbytes = 0;
  174                 explicit_bzero(chacha20->m_buffer, CHACHA20_BUFFER_SIZE);
  175                 explicit_bzero(&chacha20->ctx, sizeof(chacha20->ctx));
  176         }
  177 }
  178 SYSINIT(chacha20, SI_SUB_LOCK, SI_ORDER_ANY, chacha20_init, NULL);
  179 
  180 
  181 static void
  182 chacha20_uninit(void)
  183 {
  184         struct chacha20_s *chacha20;
  185 
  186         CHACHA20_FOREACH(chacha20)
  187                 mtx_destroy(&chacha20->mtx);
  188         free(chacha20inst, M_CHACHA20RANDOM);
  189 }
  190 SYSUNINIT(chacha20, SI_SUB_LOCK, SI_ORDER_ANY, chacha20_uninit, NULL);
  191 
  192 
  193 /*
  194  * MPSAFE
  195  */
  196 void
  197 arc4rand(void *ptr, u_int len, int reseed)
  198 {
  199         struct chacha20_s *chacha20;
  200         struct timeval tv;
  201         u_int length;
  202         uint8_t *p;
  203 
  204 #ifdef RANDOM_FENESTRASX
  205         if (__predict_false(reseed))
  206 #else
  207         if (__predict_false(reseed ||
  208             (arc4rand_iniseed_state == ARC4_ENTR_HAVE &&
  209             atomic_cmpset_int(&arc4rand_iniseed_state, ARC4_ENTR_HAVE, ARC4_ENTR_SEED))))
  210 #endif
  211                 CHACHA20_FOREACH(chacha20)
  212                         chacha20_randomstir(chacha20);
  213 
  214         getmicrouptime(&tv);
  215         chacha20 = &chacha20inst[curcpu];
  216         /* We may get unlucky and be migrated off this CPU, but that is expected to be infrequent */
  217         if ((chacha20->numbytes > CHACHA20_RESEED_BYTES) || (tv.tv_sec > chacha20->t_reseed))
  218                 chacha20_randomstir(chacha20);
  219 
  220         mtx_lock(&chacha20->mtx);
  221 #ifdef RANDOM_FENESTRASX
  222         if (__predict_false(
  223             atomic_load_acq_64(&fxrng_root_generation) != chacha20->seed_version
  224             )) {
  225                 mtx_unlock(&chacha20->mtx);
  226                 chacha20_randomstir(chacha20);
  227                 mtx_lock(&chacha20->mtx);
  228         }
  229 #endif
  230 
  231         p = ptr;
  232         while (len) {
  233                 length = MIN(CHACHA20_BUFFER_SIZE, len);
  234                 chacha_encrypt_bytes(&chacha20->ctx, chacha20->m_buffer, p, length);
  235                 p += length;
  236                 len -= length;
  237                 chacha20->numbytes += length;
  238                 if (chacha20->numbytes > CHACHA20_RESEED_BYTES) {
  239                         mtx_unlock(&chacha20->mtx);
  240                         chacha20_randomstir(chacha20);
  241                         mtx_lock(&chacha20->mtx);
  242                 }
  243         }
  244         mtx_unlock(&chacha20->mtx);
  245 }
  246 
  247 uint32_t
  248 arc4random(void)
  249 {
  250         uint32_t ret;
  251 
  252         arc4rand(&ret, sizeof(ret), 0);
  253         return ret;
  254 }
  255 
  256 void
  257 arc4random_buf(void *ptr, size_t len)
  258 {
  259 
  260         arc4rand(ptr, len, 0);
  261 }

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FreeBSD/Linux Kernel Cross Reference sys/libkern/arc4random.c

FreeBSD/Linux Kernel Cross Reference
sys/libkern/arc4random.c