the-tree/crypto/ansi_cprng.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * PRNG: Pseudo Random Number Generator
0004  *       Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
0005  *       AES 128 cipher
0006  *
0007  *  (C) Neil Horman <nhorman@tuxdriver.com>
0008  */
0009
0010 #include <crypto/internal/cipher.h>
0011 #include <crypto/internal/rng.h>
0012 #include <linux/err.h>
0013 #include <linux/init.h>
0014 #include <linux/module.h>
0015 #include <linux/moduleparam.h>
0016 #include <linux/string.h>
0017
0018 #define DEFAULT_PRNG_KEY "0123456789abcdef"
0019 #define DEFAULT_PRNG_KSZ 16
0020 #define DEFAULT_BLK_SZ 16
0021 #define DEFAULT_V_SEED "zaybxcwdveuftgsh"
0022
0023 /*
0024  * Flags for the prng_context flags field
0025  */
0026
0027 #define PRNG_FIXED_SIZE 0x1
0028 #define PRNG_NEED_RESET 0x2
0029
0030 /*
0031  * Note: DT is our counter value
0032  *   I is our intermediate value
0033  *   V is our seed vector
0034  * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
0035  * for implementation details
0036  */
0037
0038
0039 struct prng_context {
0040     spinlock_t prng_lock;
0041     unsigned char rand_data[DEFAULT_BLK_SZ];
0042     unsigned char last_rand_data[DEFAULT_BLK_SZ];
0043     unsigned char DT[DEFAULT_BLK_SZ];
0044     unsigned char I[DEFAULT_BLK_SZ];
0045     unsigned char V[DEFAULT_BLK_SZ];
0046     u32 rand_data_valid;
0047     struct crypto_cipher *tfm;
0048     u32 flags;
0049 };
0050
0051 static int dbg;
0052
0053 static void hexdump(char *note, unsigned char *buf, unsigned int len)
0054 {
0055     if (dbg) {
0056         printk(KERN_CRIT "%s", note);
0057         print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
0058                 16, 1,
0059                 buf, len, false);
0060     }
0061 }
0062
0063 #define dbgprint(format, args...) do {\
0064 if (dbg)\
0065     printk(format, ##args);\
0066 } while (0)
0067
0068 static void xor_vectors(unsigned char *in1, unsigned char *in2,
0069             unsigned char *out, unsigned int size)
0070 {
0071     int i;
0072
0073     for (i = 0; i < size; i++)
0074         out[i] = in1[i] ^ in2[i];
0075
0076 }
0077 /*
0078  * Returns DEFAULT_BLK_SZ bytes of random data per call
0079  * returns 0 if generation succeeded, <0 if something went wrong
0080  */
0081 static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
0082 {
0083     int i;
0084     unsigned char tmp[DEFAULT_BLK_SZ];
0085     unsigned char *output = NULL;
0086
0087
0088     dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
0089         ctx);
0090
0091     hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
0092     hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
0093     hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
0094
0095     /*
0096      * This algorithm is a 3 stage state machine
0097      */
0098     for (i = 0; i < 3; i++) {
0099
0100         switch (i) {
0101         case 0:
0102             /*
0103              * Start by encrypting the counter value
0104              * This gives us an intermediate value I
0105              */
0106             memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
0107             output = ctx->I;
0108             hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
0109             break;
0110         case 1:
0111
0112             /*
0113              * Next xor I with our secret vector V
0114              * encrypt that result to obtain our
0115              * pseudo random data which we output
0116              */
0117             xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
0118             hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
0119             output = ctx->rand_data;
0120             break;
0121         case 2:
0122             /*
0123              * First check that we didn't produce the same
0124              * random data that we did last time around through this
0125              */
0126             if (!memcmp(ctx->rand_data, ctx->last_rand_data,
0127                     DEFAULT_BLK_SZ)) {
0128                 if (cont_test) {
0129                     panic("cprng %p Failed repetition check!\n",
0130                         ctx);
0131                 }
0132
0133                 printk(KERN_ERR
0134                     "ctx %p Failed repetition check!\n",
0135                     ctx);
0136
0137                 ctx->flags |= PRNG_NEED_RESET;
0138                 return -EINVAL;
0139             }
0140             memcpy(ctx->last_rand_data, ctx->rand_data,
0141                 DEFAULT_BLK_SZ);
0142
0143             /*
0144              * Lastly xor the random data with I
0145              * and encrypt that to obtain a new secret vector V
0146              */
0147             xor_vectors(ctx->rand_data, ctx->I, tmp,
0148                 DEFAULT_BLK_SZ);
0149             output = ctx->V;
0150             hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
0151             break;
0152         }
0153
0154
0155         /* do the encryption */
0156         crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
0157
0158     }
0159
0160     /*
0161      * Now update our DT value
0162      */
0163     for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
0164         ctx->DT[i] += 1;
0165         if (ctx->DT[i] != 0)
0166             break;
0167     }
0168
0169     dbgprint("Returning new block for context %p\n", ctx);
0170     ctx->rand_data_valid = 0;
0171
0172     hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
0173     hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
0174     hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
0175     hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
0176
0177     return 0;
0178 }
0179
0180 /* Our exported functions */
0181 static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
0182                 int do_cont_test)
0183 {
0184     unsigned char *ptr = buf;
0185     unsigned int byte_count = (unsigned int)nbytes;
0186     int err;
0187
0188
0189     spin_lock_bh(&ctx->prng_lock);
0190
0191     err = -EINVAL;
0192     if (ctx->flags & PRNG_NEED_RESET)
0193         goto done;
0194
0195     /*
0196      * If the FIXED_SIZE flag is on, only return whole blocks of
0197      * pseudo random data
0198      */
0199     err = -EINVAL;
0200     if (ctx->flags & PRNG_FIXED_SIZE) {
0201         if (nbytes < DEFAULT_BLK_SZ)
0202             goto done;
0203         byte_count = DEFAULT_BLK_SZ;
0204     }
0205
0206     /*
0207      * Return 0 in case of success as mandated by the kernel
0208      * crypto API interface definition.
0209      */
0210     err = 0;
0211
0212     dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
0213         byte_count, ctx);
0214
0215
0216 remainder:
0217     if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
0218         if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
0219             memset(buf, 0, nbytes);
0220             err = -EINVAL;
0221             goto done;
0222         }
0223     }
0224
0225     /*
0226      * Copy any data less than an entire block
0227      */
0228     if (byte_count < DEFAULT_BLK_SZ) {
0229 empty_rbuf:
0230         while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
0231             *ptr = ctx->rand_data[ctx->rand_data_valid];
0232             ptr++;
0233             byte_count--;
0234             ctx->rand_data_valid++;
0235             if (byte_count == 0)
0236                 goto done;
0237         }
0238     }
0239
0240     /*
0241      * Now copy whole blocks
0242      */
0243     for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
0244         if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
0245             if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
0246                 memset(buf, 0, nbytes);
0247                 err = -EINVAL;
0248                 goto done;
0249             }
0250         }
0251         if (ctx->rand_data_valid > 0)
0252             goto empty_rbuf;
0253         memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
0254         ctx->rand_data_valid += DEFAULT_BLK_SZ;
0255         ptr += DEFAULT_BLK_SZ;
0256     }
0257
0258     /*
0259      * Now go back and get any remaining partial block
0260      */
0261     if (byte_count)
0262         goto remainder;
0263
0264 done:
0265     spin_unlock_bh(&ctx->prng_lock);
0266     dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
0267         err, ctx);
0268     return err;
0269 }
0270
0271 static void free_prng_context(struct prng_context *ctx)
0272 {
0273     crypto_free_cipher(ctx->tfm);
0274 }
0275
0276 static int reset_prng_context(struct prng_context *ctx,
0277                   const unsigned char *key, size_t klen,
0278                   const unsigned char *V, const unsigned char *DT)
0279 {
0280     int ret;
0281     const unsigned char *prng_key;
0282
0283     spin_lock_bh(&ctx->prng_lock);
0284     ctx->flags |= PRNG_NEED_RESET;
0285
0286     prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
0287
0288     if (!key)
0289         klen = DEFAULT_PRNG_KSZ;
0290
0291     if (V)
0292         memcpy(ctx->V, V, DEFAULT_BLK_SZ);
0293     else
0294         memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
0295
0296     if (DT)
0297         memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
0298     else
0299         memset(ctx->DT, 0, DEFAULT_BLK_SZ);
0300
0301     memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
0302     memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
0303
0304     ctx->rand_data_valid = DEFAULT_BLK_SZ;
0305
0306     ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
0307     if (ret) {
0308         dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
0309             crypto_cipher_get_flags(ctx->tfm));
0310         goto out;
0311     }
0312
0313     ret = 0;
0314     ctx->flags &= ~PRNG_NEED_RESET;
0315 out:
0316     spin_unlock_bh(&ctx->prng_lock);
0317     return ret;
0318 }
0319
0320 static int cprng_init(struct crypto_tfm *tfm)
0321 {
0322     struct prng_context *ctx = crypto_tfm_ctx(tfm);
0323
0324     spin_lock_init(&ctx->prng_lock);
0325     ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
0326     if (IS_ERR(ctx->tfm)) {
0327         dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
0328                 ctx);
0329         return PTR_ERR(ctx->tfm);
0330     }
0331
0332     if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
0333         return -EINVAL;
0334
0335     /*
0336      * after allocation, we should always force the user to reset
0337      * so they don't inadvertently use the insecure default values
0338      * without specifying them intentially
0339      */
0340     ctx->flags |= PRNG_NEED_RESET;
0341     return 0;
0342 }
0343
0344 static void cprng_exit(struct crypto_tfm *tfm)
0345 {
0346     free_prng_context(crypto_tfm_ctx(tfm));
0347 }
0348
0349 static int cprng_get_random(struct crypto_rng *tfm,
0350                 const u8 *src, unsigned int slen,
0351                 u8 *rdata, unsigned int dlen)
0352 {
0353     struct prng_context *prng = crypto_rng_ctx(tfm);
0354
0355     return get_prng_bytes(rdata, dlen, prng, 0);
0356 }
0357
0358 /*
0359  *  This is the cprng_registered reset method the seed value is
0360  *  interpreted as the tuple { V KEY DT}
0361  *  V and KEY are required during reset, and DT is optional, detected
0362  *  as being present by testing the length of the seed
0363  */
0364 static int cprng_reset(struct crypto_rng *tfm,
0365                const u8 *seed, unsigned int slen)
0366 {
0367     struct prng_context *prng = crypto_rng_ctx(tfm);
0368     const u8 *key = seed + DEFAULT_BLK_SZ;
0369     const u8 *dt = NULL;
0370
0371     if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
0372         return -EINVAL;
0373
0374     if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
0375         dt = key + DEFAULT_PRNG_KSZ;
0376
0377     reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
0378
0379     if (prng->flags & PRNG_NEED_RESET)
0380         return -EINVAL;
0381     return 0;
0382 }
0383
0384 #ifdef CONFIG_CRYPTO_FIPS
0385 static int fips_cprng_get_random(struct crypto_rng *tfm,
0386                  const u8 *src, unsigned int slen,
0387                  u8 *rdata, unsigned int dlen)
0388 {
0389     struct prng_context *prng = crypto_rng_ctx(tfm);
0390
0391     return get_prng_bytes(rdata, dlen, prng, 1);
0392 }
0393
0394 static int fips_cprng_reset(struct crypto_rng *tfm,
0395                 const u8 *seed, unsigned int slen)
0396 {
0397     u8 rdata[DEFAULT_BLK_SZ];
0398     const u8 *key = seed + DEFAULT_BLK_SZ;
0399     int rc;
0400
0401     struct prng_context *prng = crypto_rng_ctx(tfm);
0402
0403     if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
0404         return -EINVAL;
0405
0406     /* fips strictly requires seed != key */
0407     if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
0408         return -EINVAL;
0409
0410     rc = cprng_reset(tfm, seed, slen);
0411
0412     if (!rc)
0413         goto out;
0414
0415     /* this primes our continuity test */
0416     rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
0417     prng->rand_data_valid = DEFAULT_BLK_SZ;
0418
0419 out:
0420     return rc;
0421 }
0422 #endif
0423
0424 static struct rng_alg rng_algs[] = { {
0425     .generate       = cprng_get_random,
0426     .seed           = cprng_reset,
0427     .seedsize       = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
0428     .base           =   {
0429         .cra_name       = "stdrng",
0430         .cra_driver_name    = "ansi_cprng",
0431         .cra_priority       = 100,
0432         .cra_ctxsize        = sizeof(struct prng_context),
0433         .cra_module     = THIS_MODULE,
0434         .cra_init       = cprng_init,
0435         .cra_exit       = cprng_exit,
0436     }
0437 #ifdef CONFIG_CRYPTO_FIPS
0438 }, {
0439     .generate       = fips_cprng_get_random,
0440     .seed           = fips_cprng_reset,
0441     .seedsize       = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
0442     .base           =   {
0443         .cra_name       = "fips(ansi_cprng)",
0444         .cra_driver_name    = "fips_ansi_cprng",
0445         .cra_priority       = 300,
0446         .cra_ctxsize        = sizeof(struct prng_context),
0447         .cra_module     = THIS_MODULE,
0448         .cra_init       = cprng_init,
0449         .cra_exit       = cprng_exit,
0450     }
0451 #endif
0452 } };
0453
0454 /* Module initalization */
0455 static int __init prng_mod_init(void)
0456 {
0457     return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
0458 }
0459
0460 static void __exit prng_mod_fini(void)
0461 {
0462     crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
0463 }
0464
0465 MODULE_LICENSE("GPL");
0466 MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
0467 MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
0468 module_param(dbg, int, 0);
0469 MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
0470 subsys_initcall(prng_mod_init);
0471 module_exit(prng_mod_fini);
0472 MODULE_ALIAS_CRYPTO("stdrng");
0473 MODULE_ALIAS_CRYPTO("ansi_cprng");
0474 MODULE_IMPORT_NS(CRYPTO_INTERNAL);