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);
475
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