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, prefix_str: "" , prefix_type: DUMP_PREFIX_OFFSET, |
58 | rowsize: 16, groupsize: 1, |
59 | buf, len, ascii: 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(note: "Input DT: " , buf: ctx->DT, DEFAULT_BLK_SZ); |
92 | hexdump(note: "Input I: " , buf: ctx->I, DEFAULT_BLK_SZ); |
93 | hexdump(note: "Input V: " , buf: 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(note: "tmp stage 0: " , buf: 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(in1: ctx->I, in2: ctx->V, out: tmp, DEFAULT_BLK_SZ); |
118 | hexdump(note: "tmp stage 1: " , buf: 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(p: ctx->rand_data, q: ctx->last_rand_data, |
127 | DEFAULT_BLK_SZ)) { |
128 | if (cont_test) { |
129 | panic(fmt: "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(in1: ctx->rand_data, in2: ctx->I, out: tmp, |
148 | DEFAULT_BLK_SZ); |
149 | output = ctx->V; |
150 | hexdump(note: "tmp stage 2: " , buf: tmp, DEFAULT_BLK_SZ); |
151 | break; |
152 | } |
153 | |
154 | |
155 | /* do the encryption */ |
156 | crypto_cipher_encrypt_one(tfm: ctx->tfm, dst: output, src: 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(note: "Output DT: " , buf: ctx->DT, DEFAULT_BLK_SZ); |
173 | hexdump(note: "Output I: " , buf: ctx->I, DEFAULT_BLK_SZ); |
174 | hexdump(note: "Output V: " , buf: ctx->V, DEFAULT_BLK_SZ); |
175 | hexdump(note: "New Random Data: " , buf: 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(lock: &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, cont_test: 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, cont_test: 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(lock: &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(tfm: 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(lock: &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(tfm: ctx->tfm, key: prng_key, keylen: 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(lock: &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(alg_name: "aes" , type: 0, mask: 0); |
326 | if (IS_ERR(ptr: ctx->tfm)) { |
327 | dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n" , |
328 | ctx); |
329 | return PTR_ERR(ptr: 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(ctx: 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(buf: rdata, nbytes: dlen, ctx: prng, do_cont_test: 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(ctx: prng, key, DEFAULT_PRNG_KSZ, V: seed, DT: 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(algs: rng_algs, ARRAY_SIZE(rng_algs)); |
458 | } |
459 | |
460 | static void __exit prng_mod_fini(void) |
461 | { |
462 | crypto_unregister_rngs(algs: 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 | |