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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * PRNG: Pseudo Random Number Generator4 * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using5 * AES 128 cipher6 *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 1620#define DEFAULT_BLK_SZ 1621#define DEFAULT_V_SEED "zaybxcwdveuftgsh"22 23/*24 * Flags for the prng_context flags field25 */26 27#define PRNG_FIXED_SIZE 0x128#define PRNG_NEED_RESET 0x229 30/*31 * Note: DT is our counter value32 * I is our intermediate value33 * V is our seed vector34 * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf35 * for implementation details36 */37 38 39struct 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 51static int dbg;52 53static 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 {\64if (dbg)\65 printk(format, ##args);\66} while (0)67 68static 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 call79 * returns 0 if generation succeeded, <0 if something went wrong80 */81static 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 machine97 */98 for (i = 0; i < 3; i++) {99 100 switch (i) {101 case 0:102 /*103 * Start by encrypting the counter value104 * This gives us an intermediate value I105 */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 V114 * encrypt that result to obtain our115 * pseudo random data which we output116 */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 same124 * random data that we did last time around through this125 */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_ERR134 "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 I145 * and encrypt that to obtain a new secret vector V146 */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 value162 */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 */181static 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 of197 * pseudo random data198 */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 kernel208 * 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 216remainder: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 block227 */228 if (byte_count < DEFAULT_BLK_SZ) {229empty_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 blocks242 */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 block260 */261 if (byte_count)262 goto remainder;263 264done: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 271static void free_prng_context(struct prng_context *ctx)272{273 crypto_free_cipher(ctx->tfm);274}275 276static 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 else294 memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);295 296 if (DT)297 memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);298 else299 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;315out:316 spin_unlock_bh(&ctx->prng_lock);317 return ret;318}319 320static 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 reset337 * so they don't inadvertently use the insecure default values338 * without specifying them intentially339 */340 ctx->flags |= PRNG_NEED_RESET;341 return 0;342}343 344static void cprng_exit(struct crypto_tfm *tfm)345{346 free_prng_context(crypto_tfm_ctx(tfm));347}348 349static 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 is360 * interpreted as the tuple { V KEY DT}361 * V and KEY are required during reset, and DT is optional, detected362 * as being present by testing the length of the seed363 */364static 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_FIPS385static 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 394static 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 419out:420 return rc;421}422#endif423 424static 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_FIPS438}, {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#endif452} };453 454/* Module initalization */455static int __init prng_mod_init(void)456{457 return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));458}459 460static void __exit prng_mod_fini(void)461{462 crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));463}464 465MODULE_LICENSE("GPL");466MODULE_DESCRIPTION("Software Pseudo Random Number Generator");467MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");468module_param(dbg, int, 0);469MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");470subsys_initcall(prng_mod_init);471module_exit(prng_mod_fini);472MODULE_ALIAS_CRYPTO("stdrng");473MODULE_ALIAS_CRYPTO("ansi_cprng");474MODULE_IMPORT_NS(CRYPTO_INTERNAL);475