Line data Source code
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 0 : static void hexdump(char *note, unsigned char *buf, unsigned int len)
54 : {
55 0 : if (dbg) {
56 0 : printk(KERN_CRIT "%s", note);
57 0 : print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
58 : 16, 1,
59 : buf, len, false);
60 : }
61 0 : }
62 :
63 : #define dbgprint(format, args...) do {\
64 : if (dbg)\
65 : printk(format, ##args);\
66 : } while (0)
67 :
68 0 : static void xor_vectors(unsigned char *in1, unsigned char *in2,
69 : unsigned char *out, unsigned int size)
70 : {
71 0 : int i;
72 :
73 0 : for (i = 0; i < size; i++)
74 0 : 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 0 : static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
82 : {
83 0 : int i;
84 0 : unsigned char tmp[DEFAULT_BLK_SZ];
85 0 : unsigned char *output = NULL;
86 :
87 :
88 0 : dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
89 : ctx);
90 :
91 0 : hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
92 0 : hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
93 0 : hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
94 :
95 : /*
96 : * This algorithm is a 3 stage state machine
97 : */
98 0 : for (i = 0; i < 3; i++) {
99 :
100 0 : switch (i) {
101 0 : case 0:
102 : /*
103 : * Start by encrypting the counter value
104 : * This gives us an intermediate value I
105 : */
106 0 : memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
107 0 : output = ctx->I;
108 0 : hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
109 0 : 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 0 : xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
118 0 : hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
119 0 : output = ctx->rand_data;
120 0 : break;
121 0 : 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 0 : if (!memcmp(ctx->rand_data, ctx->last_rand_data,
127 : DEFAULT_BLK_SZ)) {
128 0 : if (cont_test) {
129 0 : panic("cprng %p Failed repetition check!\n",
130 : ctx);
131 : }
132 :
133 0 : printk(KERN_ERR
134 : "ctx %p Failed repetition check!\n",
135 : ctx);
136 :
137 0 : ctx->flags |= PRNG_NEED_RESET;
138 0 : return -EINVAL;
139 : }
140 0 : 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 0 : xor_vectors(ctx->rand_data, ctx->I, tmp,
148 : DEFAULT_BLK_SZ);
149 0 : output = ctx->V;
150 0 : hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
151 0 : break;
152 : }
153 :
154 :
155 : /* do the encryption */
156 0 : crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
157 :
158 : }
159 :
160 : /*
161 : * Now update our DT value
162 : */
163 0 : for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
164 0 : ctx->DT[i] += 1;
165 0 : if (ctx->DT[i] != 0)
166 : break;
167 : }
168 :
169 0 : dbgprint("Returning new block for context %p\n", ctx);
170 0 : ctx->rand_data_valid = 0;
171 :
172 0 : hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
173 0 : hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
174 0 : hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
175 0 : hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
176 :
177 0 : return 0;
178 : }
179 :
180 : /* Our exported functions */
181 0 : static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx,
182 : int do_cont_test)
183 : {
184 0 : unsigned char *ptr = buf;
185 0 : unsigned int byte_count = (unsigned int)nbytes;
186 0 : int err;
187 :
188 :
189 0 : spin_lock_bh(&ctx->prng_lock);
190 :
191 0 : err = -EINVAL;
192 0 : if (ctx->flags & PRNG_NEED_RESET)
193 0 : goto done;
194 :
195 : /*
196 : * If the FIXED_SIZE flag is on, only return whole blocks of
197 : * pseudo random data
198 : */
199 0 : err = -EINVAL;
200 0 : if (ctx->flags & PRNG_FIXED_SIZE) {
201 0 : if (nbytes < DEFAULT_BLK_SZ)
202 0 : 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 0 : err = 0;
211 :
212 0 : dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
213 : byte_count, ctx);
214 :
215 :
216 0 : remainder:
217 0 : if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
218 0 : if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
219 0 : memset(buf, 0, nbytes);
220 0 : err = -EINVAL;
221 0 : goto done;
222 : }
223 : }
224 :
225 : /*
226 : * Copy any data less than an entire block
227 : */
228 0 : if (byte_count < DEFAULT_BLK_SZ) {
229 0 : empty_rbuf:
230 0 : while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
231 0 : *ptr = ctx->rand_data[ctx->rand_data_valid];
232 0 : ptr++;
233 0 : byte_count--;
234 0 : ctx->rand_data_valid++;
235 0 : if (byte_count == 0)
236 0 : goto done;
237 : }
238 : }
239 :
240 : /*
241 : * Now copy whole blocks
242 : */
243 0 : for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
244 0 : if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
245 0 : if (_get_more_prng_bytes(ctx, do_cont_test) < 0) {
246 0 : memset(buf, 0, nbytes);
247 0 : err = -EINVAL;
248 0 : goto done;
249 : }
250 : }
251 0 : if (ctx->rand_data_valid > 0)
252 0 : goto empty_rbuf;
253 0 : memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
254 0 : ctx->rand_data_valid += DEFAULT_BLK_SZ;
255 0 : ptr += DEFAULT_BLK_SZ;
256 : }
257 :
258 : /*
259 : * Now go back and get any remaining partial block
260 : */
261 0 : if (byte_count)
262 0 : goto remainder;
263 :
264 0 : done:
265 0 : spin_unlock_bh(&ctx->prng_lock);
266 0 : dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
267 : err, ctx);
268 0 : return err;
269 : }
270 :
271 0 : static void free_prng_context(struct prng_context *ctx)
272 : {
273 0 : crypto_free_cipher(ctx->tfm);
274 : }
275 :
276 0 : 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 0 : int ret;
281 0 : const unsigned char *prng_key;
282 :
283 0 : spin_lock_bh(&ctx->prng_lock);
284 0 : ctx->flags |= PRNG_NEED_RESET;
285 :
286 0 : prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
287 :
288 0 : if (!key)
289 0 : klen = DEFAULT_PRNG_KSZ;
290 :
291 0 : if (V)
292 0 : memcpy(ctx->V, V, DEFAULT_BLK_SZ);
293 : else
294 0 : memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
295 :
296 0 : if (DT)
297 0 : memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
298 : else
299 0 : memset(ctx->DT, 0, DEFAULT_BLK_SZ);
300 :
301 0 : memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
302 0 : memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
303 :
304 0 : ctx->rand_data_valid = DEFAULT_BLK_SZ;
305 :
306 0 : ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
307 0 : if (ret) {
308 0 : dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
309 : crypto_cipher_get_flags(ctx->tfm));
310 0 : goto out;
311 : }
312 :
313 0 : ret = 0;
314 0 : ctx->flags &= ~PRNG_NEED_RESET;
315 0 : out:
316 0 : spin_unlock_bh(&ctx->prng_lock);
317 0 : return ret;
318 : }
319 :
320 0 : static int cprng_init(struct crypto_tfm *tfm)
321 : {
322 0 : struct prng_context *ctx = crypto_tfm_ctx(tfm);
323 :
324 0 : spin_lock_init(&ctx->prng_lock);
325 0 : ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
326 0 : if (IS_ERR(ctx->tfm)) {
327 0 : dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
328 : ctx);
329 0 : return PTR_ERR(ctx->tfm);
330 : }
331 :
332 0 : 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 0 : ctx->flags |= PRNG_NEED_RESET;
341 0 : return 0;
342 : }
343 :
344 0 : static void cprng_exit(struct crypto_tfm *tfm)
345 : {
346 0 : free_prng_context(crypto_tfm_ctx(tfm));
347 0 : }
348 :
349 0 : static int cprng_get_random(struct crypto_rng *tfm,
350 : const u8 *src, unsigned int slen,
351 : u8 *rdata, unsigned int dlen)
352 : {
353 0 : struct prng_context *prng = crypto_rng_ctx(tfm);
354 :
355 0 : 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 0 : static int cprng_reset(struct crypto_rng *tfm,
365 : const u8 *seed, unsigned int slen)
366 : {
367 0 : struct prng_context *prng = crypto_rng_ctx(tfm);
368 0 : const u8 *key = seed + DEFAULT_BLK_SZ;
369 0 : const u8 *dt = NULL;
370 :
371 0 : if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
372 : return -EINVAL;
373 :
374 0 : if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
375 0 : dt = key + DEFAULT_PRNG_KSZ;
376 :
377 0 : reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
378 :
379 0 : if (prng->flags & PRNG_NEED_RESET)
380 0 : 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 1 : static int __init prng_mod_init(void)
456 : {
457 1 : return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
458 : }
459 :
460 0 : static void __exit prng_mod_fini(void)
461 : {
462 0 : crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
463 0 : }
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);
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