crypto/ansi_cprng.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * PRNG: Pseudo Random Number Generator
   4  *       Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
   5  *       AES 128 cipher
   6  *
   7  *  (C) Neil Horman <nhorman@tuxdriver.com>
   8  */
   9
  10 #include <crypto/internal/cipher.h>
  11 #include <crypto/internal/rng.h>
  12 #include <linux/err.h>
  13 #include <linux/init.h>
  14 #include <linux/module.h>
  15 #include <linux/moduleparam.h>
  16 #include <linux/string.h>
  17
  18 #define DEFAULT_PRNG_KEY "0123456789abcdef"
  19 #define DEFAULT_PRNG_KSZ 16
  20 #define DEFAULT_BLK_SZ 16
  21 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
  22
  23 /*
  24  * Flags for the prng_context flags field
  25  */
  26
  27 #define PRNG_FIXED_SIZE 0x1
  28 #define PRNG_NEED_RESET 0x2
  29
  30 /*
  31  * Note: DT is our counter value
  32  *       I is our intermediate value
  33  *       V is our seed vector
  34  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
  35  * for implementation details
  36  */
  37
  38
  39 struct prng_context {
  40         spinlock_t prng_lock;
  41         unsigned char rand_data[DEFAULT_BLK_SZ];
  42         unsigned char last_rand_data[DEFAULT_BLK_SZ];
  43         unsigned char DT[DEFAULT_BLK_SZ];
  44         unsigned char I[DEFAULT_BLK_SZ];
  45         unsigned char V[DEFAULT_BLK_SZ];
  46         u32 rand_data_valid;
  47         struct crypto_cipher *tfm;
  48         u32 flags;
  49 };
  50
  51 static int dbg;
  52
  53 static void hexdump(char *note, unsigned char *buf, unsigned int len)
  54 {
  55         if (dbg) {
  56                 printk(KERN_CRIT "%s", note);
  57                 print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
  58                                 16, 1,
  59                                 buf, len, false);
  60         }
  61 }
  62
  63 #define dbgprint(format, args...) do {\
  64 if (dbg)\
  65         printk(format, ##args);\
  66 } while (0)
  67
  68 static void xor_vectors(unsigned char *in1, unsigned char *in2,
  69                         unsigned char *out, unsigned int size)
  70 {
  71         int i;
  72
  73         for (i = 0; i < size; i++)
  74                 out[i] = in1[i] ^ in2[i];
  75
  76 }
  77 /*
  78  * Returns DEFAULT_BLK_SZ bytes of random data per call
  79  * returns 0 if generation succeeded, <0 if something went wrong
  80  */
  81 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
  82 {
  83         int i;
  84         unsigned char tmp[DEFAULT_BLK_SZ];
  85         unsigned char *output = NULL;
  86
  87
  88         dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
  89                 ctx);
  90
  91         hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
  92         hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
  93         hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
  94
  95         /*
  96          * This algorithm is a 3 stage state machine
  97          */
  98         for (i = 0; i < 3; i++) {
  99
 100                 switch (i) {
 101                 case 0:
 102                         /*
 103                          * Start by encrypting the counter value
 104                          * This gives us an intermediate value I
 105                          */
 106                         memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
 107                         output = ctx->I;
 108                         hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
 109                         break;
 110                 case 1:
 111
 112                         /*
 113                          * Next xor I with our secret vector V
 114                          * encrypt that result to obtain our
 115                          * pseudo random data which we output
 116                          */
 117                         xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
 118                         hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
 119                         output = ctx->rand_data;
 120                         break;
 121                 case 2:
 122                         /*
 123                          * First check that we didn't produce the same
 124                          * random data that we did last time around through this
 125                          */
 126                         if (!memcmp(ctx->rand_data, ctx->last_rand_data,
 127                                         DEFAULT_BLK_SZ)) {
 128                                 if (cont_test) {
 129                                         panic("cprng %p Failed repetition check!\n",
 130                                                 ctx);
 131                                 }
 132
 133                                 printk(KERN_ERR
 134                                         "ctx %p Failed repetition check!\n",
 135                                         ctx);
 136
 137                                 ctx->flags |= PRNG_NEED_RESET;
 138                                 return -EINVAL;
 139                         }
 140                         memcpy(ctx->last_rand_data, ctx->rand_data,
 141                                 DEFAULT_BLK_SZ);
 142
 143                         /*
 144                          * Lastly xor the random data with I
 145                          * and encrypt that to obtain a new secret vector V
 146                          */
 147                         xor_vectors(ctx->rand_data, ctx->I, tmp,
 148                                 DEFAULT_BLK_SZ);
 149                         output = ctx->V;
 150                         hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
 151                         break;
 152                 }
 153
 154
 155                 /* do the encryption */
 156                 crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
 157
 158         }
 159
 160         /*
 161          * Now update our DT value
 162          */
 163         for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
 164                 ctx->DT[i] += 1;
 165                 if (ctx->DT[i] != 0)
 166                         break;
 167         }
 168
 169         dbgprint("Returning new block for context %p\n", ctx);
 170         ctx->rand_data_valid = 0;
 171
 172         hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
 173         hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
 174         hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
 175         hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
 176
 177         return 0;
 178 }
 179
 180 /* Our exported functions */
 181 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
 182                                 int do_cont_test)
 183 {
 184         unsigned char *ptr = buf;
 185         unsigned int byte_count = (unsigned int)nbytes;
 186         int err;
 187
 188
 189         spin_lock_bh(&ctx->prng_lock);
 190
 191         err = -EINVAL;
 192         if (ctx->flags & PRNG_NEED_RESET)
 193                 goto done;
 194
 195         /*
 196          * If the FIXED_SIZE flag is on, only return whole blocks of
 197          * pseudo random data
 198          */
 199         err = -EINVAL;
 200         if (ctx->flags & PRNG_FIXED_SIZE) {
 201                 if (nbytes < DEFAULT_BLK_SZ)
 202                         goto done;
 203                 byte_count = DEFAULT_BLK_SZ;
 204         }
 205
 206         /*
 207          * Return 0 in case of success as mandated by the kernel
 208          * crypto API interface definition.
 209          */
 210         err = 0;
 211
 212         dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
 213                 byte_count, ctx);
 214
 215
 216 remainder:
 217         if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 218                 if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
 219                         memset(buf, 0, nbytes);
 220                         err = -EINVAL;
 221                         goto done;
 222                 }
 223         }
 224
 225         /*
 226          * Copy any data less than an entire block
 227          */
 228         if (byte_count < DEFAULT_BLK_SZ) {
 229 empty_rbuf:
 230                 while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
 231                         *ptr = ctx->rand_data[ctx->rand_data_valid];
 232                         ptr++;
 233                         byte_count--;
 234                         ctx->rand_data_valid++;
 235                         if (byte_count == 0)
 236                                 goto done;
 237                 }
 238         }
 239
 240         /*
 241          * Now copy whole blocks
 242          */
 243         for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
 244                 if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
 245                         if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
 246                                 memset(buf, 0, nbytes);
 247                                 err = -EINVAL;
 248                                 goto done;
 249                         }
 250                 }
 251                 if (ctx->rand_data_valid > 0)
 252                         goto empty_rbuf;
 253                 memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
 254                 ctx->rand_data_valid += DEFAULT_BLK_SZ;
 255                 ptr += DEFAULT_BLK_SZ;
 256         }
 257
 258         /*
 259          * Now go back and get any remaining partial block
 260          */
 261         if (byte_count)
 262                 goto remainder;
 263
 264 done:
 265         spin_unlock_bh(&ctx->prng_lock);
 266         dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
 267                 err, ctx);
 268         return err;
 269 }
 270
 271 static void free_prng_context(struct prng_context *ctx)
 272 {
 273         crypto_free_cipher(ctx->tfm);
 274 }
 275
 276 static int reset_prng_context(struct prng_context *ctx,
 277                               const unsigned char *key, size_t klen,
 278                               const unsigned char *V, const unsigned char *DT)
 279 {
 280         int ret;
 281         const unsigned char *prng_key;
 282
 283         spin_lock_bh(&ctx->prng_lock);
 284         ctx->flags |= PRNG_NEED_RESET;
 285
 286         prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
 287
 288         if (!key)
 289                 klen = DEFAULT_PRNG_KSZ;
 290
 291         if (V)
 292                 memcpy(ctx->V, V, DEFAULT_BLK_SZ);
 293         else
 294                 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
 295
 296         if (DT)
 297                 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
 298         else
 299                 memset(ctx->DT, 0, DEFAULT_BLK_SZ);
 300
 301         memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
 302         memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
 303
 304         ctx->rand_data_valid = DEFAULT_BLK_SZ;
 305
 306         ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
 307         if (ret) {
 308                 dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
 309                         crypto_cipher_get_flags(ctx->tfm));
 310                 goto out;
 311         }
 312
 313         ret = 0;
 314         ctx->flags &= ~PRNG_NEED_RESET;
 315 out:
 316         spin_unlock_bh(&ctx->prng_lock);
 317         return ret;
 318 }
 319
 320 static int cprng_init(struct crypto_tfm *tfm)
 321 {
 322         struct prng_context *ctx = crypto_tfm_ctx(tfm);
 323
 324         spin_lock_init(&ctx->prng_lock);
 325         ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
 326         if (IS_ERR(ctx->tfm)) {
 327                 dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
 328                                 ctx);
 329                 return PTR_ERR(ctx->tfm);
 330         }
 331
 332         if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
 333                 return -EINVAL;
 334
 335         /*
 336          * after allocation, we should always force the user to reset
 337          * so they don't inadvertently use the insecure default values
 338          * without specifying them intentially
 339          */
 340         ctx->flags |= PRNG_NEED_RESET;
 341         return 0;
 342 }
 343
 344 static void cprng_exit(struct crypto_tfm *tfm)
 345 {
 346         free_prng_context(crypto_tfm_ctx(tfm));
 347 }
 348
 349 static int cprng_get_random(struct crypto_rng *tfm,
 350                             const u8 *src, unsigned int slen,
 351                             u8 *rdata, unsigned int dlen)
 352 {
 353         struct prng_context *prng = crypto_rng_ctx(tfm);
 354
 355         return get_prng_bytes(rdata, dlen, prng, 0);
 356 }
 357
 358 /*
 359  *  This is the cprng_registered reset method the seed value is
 360  *  interpreted as the tuple { V KEY DT}
 361  *  V and KEY are required during reset, and DT is optional, detected
 362  *  as being present by testing the length of the seed
 363  */
 364 static int cprng_reset(struct crypto_rng *tfm,
 365                        const u8 *seed, unsigned int slen)
 366 {
 367         struct prng_context *prng = crypto_rng_ctx(tfm);
 368         const u8 *key = seed + DEFAULT_BLK_SZ;
 369         const u8 *dt = NULL;
 370
 371         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 372                 return -EINVAL;
 373
 374         if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
 375                 dt = key + DEFAULT_PRNG_KSZ;
 376
 377         reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
 378
 379         if (prng->flags & PRNG_NEED_RESET)
 380                 return -EINVAL;
 381         return 0;
 382 }
 383
 384 #ifdef CONFIG_CRYPTO_FIPS
 385 static int fips_cprng_get_random(struct crypto_rng *tfm,
 386                                  const u8 *src, unsigned int slen,
 387                                  u8 *rdata, unsigned int dlen)
 388 {
 389         struct prng_context *prng = crypto_rng_ctx(tfm);
 390
 391         return get_prng_bytes(rdata, dlen, prng, 1);
 392 }
 393
 394 static int fips_cprng_reset(struct crypto_rng *tfm,
 395                             const u8 *seed, unsigned int slen)
 396 {
 397         u8 rdata[DEFAULT_BLK_SZ];
 398         const u8 *key = seed + DEFAULT_BLK_SZ;
 399         int rc;
 400
 401         struct prng_context *prng = crypto_rng_ctx(tfm);
 402
 403         if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
 404                 return -EINVAL;
 405
 406         /* fips strictly requires seed != key */
 407         if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
 408                 return -EINVAL;
 409
 410         rc = cprng_reset(tfm, seed, slen);
 411
 412         if (!rc)
 413                 goto out;
 414
 415         /* this primes our continuity test */
 416         rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
 417         prng->rand_data_valid = DEFAULT_BLK_SZ;
 418
 419 out:
 420         return rc;
 421 }
 422 #endif
 423
 424 static struct rng_alg rng_algs[] = { {
 425         .generate               = cprng_get_random,
 426         .seed                   = cprng_reset,
 427         .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
 428         .base                   =       {
 429                 .cra_name               = "stdrng",
 430                 .cra_driver_name        = "ansi_cprng",
 431                 .cra_priority           = 100,
 432                 .cra_ctxsize            = sizeof(struct prng_context),
 433                 .cra_module             = THIS_MODULE,
 434                 .cra_init               = cprng_init,
 435                 .cra_exit               = cprng_exit,
 436         }
 437 #ifdef CONFIG_CRYPTO_FIPS
 438 }, {
 439         .generate               = fips_cprng_get_random,
 440         .seed                   = fips_cprng_reset,
 441         .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
 442         .base                   =       {
 443                 .cra_name               = "fips(ansi_cprng)",
 444                 .cra_driver_name        = "fips_ansi_cprng",
 445                 .cra_priority           = 300,
 446                 .cra_ctxsize            = sizeof(struct prng_context),
 447                 .cra_module             = THIS_MODULE,
 448                 .cra_init               = cprng_init,
 449                 .cra_exit               = cprng_exit,
 450         }
 451 #endif
 452 } };
 453
 454 /* Module initalization */
 455 static int __init prng_mod_init(void)
 456 {
 457         return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
 458 }
 459
 460 static void __exit prng_mod_fini(void)
 461 {
 462         crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
 463 }
 464
 465 MODULE_LICENSE("GPL");
 466 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
 467 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
 468 module_param(dbg, int, 0);
 469 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
 470 subsys_initcall(prng_mod_init);
 471 module_exit(prng_mod_fini);
 472 MODULE_ALIAS_CRYPTO("stdrng");
 473 MODULE_ALIAS_CRYPTO("ansi_cprng");
 474 MODULE_IMPORT_NS(CRYPTO_INTERNAL);