xref: /openbmc/linux/crypto/ansi_cprng.c (revision 0eb76ba2)
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 
hexdump(char * note,unsigned char * buf,unsigned int len)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 
xor_vectors(unsigned char * in1,unsigned char * in2,unsigned char * out,unsigned int size)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  */
_get_more_prng_bytes(struct prng_context * ctx,int cont_test)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 */
get_prng_bytes(char * buf,size_t nbytes,struct prng_context * ctx,int do_cont_test)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 
free_prng_context(struct prng_context * ctx)271 static void free_prng_context(struct prng_context *ctx)
272 {
273 	crypto_free_cipher(ctx->tfm);
274 }
275 
reset_prng_context(struct prng_context * ctx,const unsigned char * key,size_t klen,const unsigned char * V,const unsigned char * DT)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 
cprng_init(struct crypto_tfm * tfm)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 
cprng_exit(struct crypto_tfm * tfm)344 static void cprng_exit(struct crypto_tfm *tfm)
345 {
346 	free_prng_context(crypto_tfm_ctx(tfm));
347 }
348 
cprng_get_random(struct crypto_rng * tfm,const u8 * src,unsigned int slen,u8 * rdata,unsigned int dlen)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  */
cprng_reset(struct crypto_rng * tfm,const u8 * seed,unsigned int slen)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
fips_cprng_get_random(struct crypto_rng * tfm,const u8 * src,unsigned int slen,u8 * rdata,unsigned int dlen)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 
fips_cprng_reset(struct crypto_rng * tfm,const u8 * seed,unsigned int slen)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 */
prng_mod_init(void)455 static int __init prng_mod_init(void)
456 {
457 	return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
458 }
459 
prng_mod_fini(void)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