xref: /linux/crypto/xts.c (revision 17cfcb68af3bc7d5e8ae08779b1853310a2949f3) 
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* XTS: as defined in IEEE1619/D16
3  *	http://grouper.ieee.org/groups/1619/email/pdf00086.pdf
4  *
5  * Copyright (c) 2007 Rik Snel <rsnel@cube.dyndns.org>
6  *
7  * Based on ecb.c
8  * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
9  */
10 #include <crypto/internal/skcipher.h>
11 #include <crypto/scatterwalk.h>
12 #include <linux/err.h>
13 #include <linux/init.h>
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/scatterlist.h>
17 #include <linux/slab.h>
18 
19 #include <crypto/xts.h>
20 #include <crypto/b128ops.h>
21 #include <crypto/gf128mul.h>
22 
23 struct priv {
24 	struct crypto_skcipher *child;
25 	struct crypto_cipher *tweak;
26 };
27 
28 struct xts_instance_ctx {
29 	struct crypto_skcipher_spawn spawn;
30 	char name[CRYPTO_MAX_ALG_NAME];
31 };
32 
33 struct rctx {
34 	le128 t;
35 	struct scatterlist *tail;
36 	struct scatterlist sg[2];
37 	struct skcipher_request subreq;
38 };
39 
40 static int setkey(struct crypto_skcipher *parent, const u8 *key,
41 		  unsigned int keylen)
42 {
43 	struct priv *ctx = crypto_skcipher_ctx(parent);
44 	struct crypto_skcipher *child;
45 	struct crypto_cipher *tweak;
46 	int err;
47 
48 	err = xts_verify_key(parent, key, keylen);
49 	if (err)
50 		return err;
51 
52 	keylen /= 2;
53 
54 	/* we need two cipher instances: one to compute the initial 'tweak'
55 	 * by encrypting the IV (usually the 'plain' iv) and the other
56 	 * one to encrypt and decrypt the data */
57 
58 	/* tweak cipher, uses Key2 i.e. the second half of *key */
59 	tweak = ctx->tweak;
60 	crypto_cipher_clear_flags(tweak, CRYPTO_TFM_REQ_MASK);
61 	crypto_cipher_set_flags(tweak, crypto_skcipher_get_flags(parent) &
62 				       CRYPTO_TFM_REQ_MASK);
63 	err = crypto_cipher_setkey(tweak, key + keylen, keylen);
64 	crypto_skcipher_set_flags(parent, crypto_cipher_get_flags(tweak) &
65 					  CRYPTO_TFM_RES_MASK);
66 	if (err)
67 		return err;
68 
69 	/* data cipher, uses Key1 i.e. the first half of *key */
70 	child = ctx->child;
71 	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
72 	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
73 					 CRYPTO_TFM_REQ_MASK);
74 	err = crypto_skcipher_setkey(child, key, keylen);
75 	crypto_skcipher_set_flags(parent, crypto_skcipher_get_flags(child) &
76 					  CRYPTO_TFM_RES_MASK);
77 
78 	return err;
79 }
80 
81 /*
82  * We compute the tweak masks twice (both before and after the ECB encryption or
83  * decryption) to avoid having to allocate a temporary buffer and/or make
84  * mutliple calls to the 'ecb(..)' instance, which usually would be slower than
85  * just doing the gf128mul_x_ble() calls again.
86  */
87 static int xor_tweak(struct skcipher_request *req, bool second_pass, bool enc)
88 {
89 	struct rctx *rctx = skcipher_request_ctx(req);
90 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
91 	const bool cts = (req->cryptlen % XTS_BLOCK_SIZE);
92 	const int bs = XTS_BLOCK_SIZE;
93 	struct skcipher_walk w;
94 	le128 t = rctx->t;
95 	int err;
96 
97 	if (second_pass) {
98 		req = &rctx->subreq;
99 		/* set to our TFM to enforce correct alignment: */
100 		skcipher_request_set_tfm(req, tfm);
101 	}
102 	err = skcipher_walk_virt(&w, req, false);
103 
104 	while (w.nbytes) {
105 		unsigned int avail = w.nbytes;
106 		le128 *wsrc;
107 		le128 *wdst;
108 
109 		wsrc = w.src.virt.addr;
110 		wdst = w.dst.virt.addr;
111 
112 		do {
113 			if (unlikely(cts) &&
114 			    w.total - w.nbytes + avail < 2 * XTS_BLOCK_SIZE) {
115 				if (!enc) {
116 					if (second_pass)
117 						rctx->t = t;
118 					gf128mul_x_ble(&t, &t);
119 				}
120 				le128_xor(wdst, &t, wsrc);
121 				if (enc && second_pass)
122 					gf128mul_x_ble(&rctx->t, &t);
123 				skcipher_walk_done(&w, avail - bs);
124 				return 0;
125 			}
126 
127 			le128_xor(wdst++, &t, wsrc++);
128 			gf128mul_x_ble(&t, &t);
129 		} while ((avail -= bs) >= bs);
130 
131 		err = skcipher_walk_done(&w, avail);
132 	}
133 
134 	return err;
135 }
136 
137 static int xor_tweak_pre(struct skcipher_request *req, bool enc)
138 {
139 	return xor_tweak(req, false, enc);
140 }
141 
142 static int xor_tweak_post(struct skcipher_request *req, bool enc)
143 {
144 	return xor_tweak(req, true, enc);
145 }
146 
147 static void cts_done(struct crypto_async_request *areq, int err)
148 {
149 	struct skcipher_request *req = areq->data;
150 	le128 b;
151 
152 	if (!err) {
153 		struct rctx *rctx = skcipher_request_ctx(req);
154 
155 		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
156 		le128_xor(&b, &rctx->t, &b);
157 		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
158 	}
159 
160 	skcipher_request_complete(req, err);
161 }
162 
163 static int cts_final(struct skcipher_request *req,
164 		     int (*crypt)(struct skcipher_request *req))
165 {
166 	struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
167 	int offset = req->cryptlen & ~(XTS_BLOCK_SIZE - 1);
168 	struct rctx *rctx = skcipher_request_ctx(req);
169 	struct skcipher_request *subreq = &rctx->subreq;
170 	int tail = req->cryptlen % XTS_BLOCK_SIZE;
171 	le128 b[2];
172 	int err;
173 
174 	rctx->tail = scatterwalk_ffwd(rctx->sg, req->dst,
175 				      offset - XTS_BLOCK_SIZE);
176 
177 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
178 	memcpy(b + 1, b, tail);
179 	scatterwalk_map_and_copy(b, req->src, offset, tail, 0);
180 
181 	le128_xor(b, &rctx->t, b);
182 
183 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE + tail, 1);
184 
185 	skcipher_request_set_tfm(subreq, ctx->child);
186 	skcipher_request_set_callback(subreq, req->base.flags, cts_done, req);
187 	skcipher_request_set_crypt(subreq, rctx->tail, rctx->tail,
188 				   XTS_BLOCK_SIZE, NULL);
189 
190 	err = crypt(subreq);
191 	if (err)
192 		return err;
193 
194 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
195 	le128_xor(b, &rctx->t, b);
196 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
197 
198 	return 0;
199 }
200 
201 static void encrypt_done(struct crypto_async_request *areq, int err)
202 {
203 	struct skcipher_request *req = areq->data;
204 
205 	if (!err) {
206 		struct rctx *rctx = skcipher_request_ctx(req);
207 
208 		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
209 		err = xor_tweak_post(req, true);
210 
211 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
212 			err = cts_final(req, crypto_skcipher_encrypt);
213 			if (err == -EINPROGRESS)
214 				return;
215 		}
216 	}
217 
218 	skcipher_request_complete(req, err);
219 }
220 
221 static void decrypt_done(struct crypto_async_request *areq, int err)
222 {
223 	struct skcipher_request *req = areq->data;
224 
225 	if (!err) {
226 		struct rctx *rctx = skcipher_request_ctx(req);
227 
228 		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
229 		err = xor_tweak_post(req, false);
230 
231 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
232 			err = cts_final(req, crypto_skcipher_decrypt);
233 			if (err == -EINPROGRESS)
234 				return;
235 		}
236 	}
237 
238 	skcipher_request_complete(req, err);
239 }
240 
241 static int init_crypt(struct skcipher_request *req, crypto_completion_t compl)
242 {
243 	struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
244 	struct rctx *rctx = skcipher_request_ctx(req);
245 	struct skcipher_request *subreq = &rctx->subreq;
246 
247 	if (req->cryptlen < XTS_BLOCK_SIZE)
248 		return -EINVAL;
249 
250 	skcipher_request_set_tfm(subreq, ctx->child);
251 	skcipher_request_set_callback(subreq, req->base.flags, compl, req);
252 	skcipher_request_set_crypt(subreq, req->dst, req->dst,
253 				   req->cryptlen & ~(XTS_BLOCK_SIZE - 1), NULL);
254 
255 	/* calculate first value of T */
256 	crypto_cipher_encrypt_one(ctx->tweak, (u8 *)&rctx->t, req->iv);
257 
258 	return 0;
259 }
260 
261 static int encrypt(struct skcipher_request *req)
262 {
263 	struct rctx *rctx = skcipher_request_ctx(req);
264 	struct skcipher_request *subreq = &rctx->subreq;
265 	int err;
266 
267 	err = init_crypt(req, encrypt_done) ?:
268 	      xor_tweak_pre(req, true) ?:
269 	      crypto_skcipher_encrypt(subreq) ?:
270 	      xor_tweak_post(req, true);
271 
272 	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
273 		return err;
274 
275 	return cts_final(req, crypto_skcipher_encrypt);
276 }
277 
278 static int decrypt(struct skcipher_request *req)
279 {
280 	struct rctx *rctx = skcipher_request_ctx(req);
281 	struct skcipher_request *subreq = &rctx->subreq;
282 	int err;
283 
284 	err = init_crypt(req, decrypt_done) ?:
285 	      xor_tweak_pre(req, false) ?:
286 	      crypto_skcipher_decrypt(subreq) ?:
287 	      xor_tweak_post(req, false);
288 
289 	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
290 		return err;
291 
292 	return cts_final(req, crypto_skcipher_decrypt);
293 }
294 
295 static int init_tfm(struct crypto_skcipher *tfm)
296 {
297 	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
298 	struct xts_instance_ctx *ictx = skcipher_instance_ctx(inst);
299 	struct priv *ctx = crypto_skcipher_ctx(tfm);
300 	struct crypto_skcipher *child;
301 	struct crypto_cipher *tweak;
302 
303 	child = crypto_spawn_skcipher(&ictx->spawn);
304 	if (IS_ERR(child))
305 		return PTR_ERR(child);
306 
307 	ctx->child = child;
308 
309 	tweak = crypto_alloc_cipher(ictx->name, 0, 0);
310 	if (IS_ERR(tweak)) {
311 		crypto_free_skcipher(ctx->child);
312 		return PTR_ERR(tweak);
313 	}
314 
315 	ctx->tweak = tweak;
316 
317 	crypto_skcipher_set_reqsize(tfm, crypto_skcipher_reqsize(child) +
318 					 sizeof(struct rctx));
319 
320 	return 0;
321 }
322 
323 static void exit_tfm(struct crypto_skcipher *tfm)
324 {
325 	struct priv *ctx = crypto_skcipher_ctx(tfm);
326 
327 	crypto_free_skcipher(ctx->child);
328 	crypto_free_cipher(ctx->tweak);
329 }
330 
331 static void free(struct skcipher_instance *inst)
332 {
333 	crypto_drop_skcipher(skcipher_instance_ctx(inst));
334 	kfree(inst);
335 }
336 
337 static int create(struct crypto_template *tmpl, struct rtattr **tb)
338 {
339 	struct skcipher_instance *inst;
340 	struct crypto_attr_type *algt;
341 	struct xts_instance_ctx *ctx;
342 	struct skcipher_alg *alg;
343 	const char *cipher_name;
344 	u32 mask;
345 	int err;
346 
347 	algt = crypto_get_attr_type(tb);
348 	if (IS_ERR(algt))
349 		return PTR_ERR(algt);
350 
351 	if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
352 		return -EINVAL;
353 
354 	cipher_name = crypto_attr_alg_name(tb[1]);
355 	if (IS_ERR(cipher_name))
356 		return PTR_ERR(cipher_name);
357 
358 	inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
359 	if (!inst)
360 		return -ENOMEM;
361 
362 	ctx = skcipher_instance_ctx(inst);
363 
364 	crypto_set_skcipher_spawn(&ctx->spawn, skcipher_crypto_instance(inst));
365 
366 	mask = crypto_requires_off(algt->type, algt->mask,
367 				   CRYPTO_ALG_NEED_FALLBACK |
368 				   CRYPTO_ALG_ASYNC);
369 
370 	err = crypto_grab_skcipher(&ctx->spawn, cipher_name, 0, mask);
371 	if (err == -ENOENT) {
372 		err = -ENAMETOOLONG;
373 		if (snprintf(ctx->name, CRYPTO_MAX_ALG_NAME, "ecb(%s)",
374 			     cipher_name) >= CRYPTO_MAX_ALG_NAME)
375 			goto err_free_inst;
376 
377 		err = crypto_grab_skcipher(&ctx->spawn, ctx->name, 0, mask);
378 	}
379 
380 	if (err)
381 		goto err_free_inst;
382 
383 	alg = crypto_skcipher_spawn_alg(&ctx->spawn);
384 
385 	err = -EINVAL;
386 	if (alg->base.cra_blocksize != XTS_BLOCK_SIZE)
387 		goto err_drop_spawn;
388 
389 	if (crypto_skcipher_alg_ivsize(alg))
390 		goto err_drop_spawn;
391 
392 	err = crypto_inst_setname(skcipher_crypto_instance(inst), "xts",
393 				  &alg->base);
394 	if (err)
395 		goto err_drop_spawn;
396 
397 	err = -EINVAL;
398 	cipher_name = alg->base.cra_name;
399 
400 	/* Alas we screwed up the naming so we have to mangle the
401 	 * cipher name.
402 	 */
403 	if (!strncmp(cipher_name, "ecb(", 4)) {
404 		unsigned len;
405 
406 		len = strlcpy(ctx->name, cipher_name + 4, sizeof(ctx->name));
407 		if (len < 2 || len >= sizeof(ctx->name))
408 			goto err_drop_spawn;
409 
410 		if (ctx->name[len - 1] != ')')
411 			goto err_drop_spawn;
412 
413 		ctx->name[len - 1] = 0;
414 
415 		if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
416 			     "xts(%s)", ctx->name) >= CRYPTO_MAX_ALG_NAME) {
417 			err = -ENAMETOOLONG;
418 			goto err_drop_spawn;
419 		}
420 	} else
421 		goto err_drop_spawn;
422 
423 	inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
424 	inst->alg.base.cra_priority = alg->base.cra_priority;
425 	inst->alg.base.cra_blocksize = XTS_BLOCK_SIZE;
426 	inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
427 				       (__alignof__(u64) - 1);
428 
429 	inst->alg.ivsize = XTS_BLOCK_SIZE;
430 	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) * 2;
431 	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) * 2;
432 
433 	inst->alg.base.cra_ctxsize = sizeof(struct priv);
434 
435 	inst->alg.init = init_tfm;
436 	inst->alg.exit = exit_tfm;
437 
438 	inst->alg.setkey = setkey;
439 	inst->alg.encrypt = encrypt;
440 	inst->alg.decrypt = decrypt;
441 
442 	inst->free = free;
443 
444 	err = skcipher_register_instance(tmpl, inst);
445 	if (err)
446 		goto err_drop_spawn;
447 
448 out:
449 	return err;
450 
451 err_drop_spawn:
452 	crypto_drop_skcipher(&ctx->spawn);
453 err_free_inst:
454 	kfree(inst);
455 	goto out;
456 }
457 
458 static struct crypto_template crypto_tmpl = {
459 	.name = "xts",
460 	.create = create,
461 	.module = THIS_MODULE,
462 };
463 
464 static int __init crypto_module_init(void)
465 {
466 	return crypto_register_template(&crypto_tmpl);
467 }
468 
469 static void __exit crypto_module_exit(void)
470 {
471 	crypto_unregister_template(&crypto_tmpl);
472 }
473 
474 subsys_initcall(crypto_module_init);
475 module_exit(crypto_module_exit);
476 
477 MODULE_LICENSE("GPL");
478 MODULE_DESCRIPTION("XTS block cipher mode");
479 MODULE_ALIAS_CRYPTO("xts");
480