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