xref: /linux/crypto/xts.c (revision f86fd32d) 
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 	if (err)
65 		return err;
66 
67 	/* data cipher, uses Key1 i.e. the first half of *key */
68 	child = ctx->child;
69 	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
70 	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
71 					 CRYPTO_TFM_REQ_MASK);
72 	return crypto_skcipher_setkey(child, key, keylen);
73 }
74 
75 /*
76  * We compute the tweak masks twice (both before and after the ECB encryption or
77  * decryption) to avoid having to allocate a temporary buffer and/or make
78  * mutliple calls to the 'ecb(..)' instance, which usually would be slower than
79  * just doing the gf128mul_x_ble() calls again.
80  */
81 static int xor_tweak(struct skcipher_request *req, bool second_pass, bool enc)
82 {
83 	struct rctx *rctx = skcipher_request_ctx(req);
84 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
85 	const bool cts = (req->cryptlen % XTS_BLOCK_SIZE);
86 	const int bs = XTS_BLOCK_SIZE;
87 	struct skcipher_walk w;
88 	le128 t = rctx->t;
89 	int err;
90 
91 	if (second_pass) {
92 		req = &rctx->subreq;
93 		/* set to our TFM to enforce correct alignment: */
94 		skcipher_request_set_tfm(req, tfm);
95 	}
96 	err = skcipher_walk_virt(&w, req, false);
97 
98 	while (w.nbytes) {
99 		unsigned int avail = w.nbytes;
100 		le128 *wsrc;
101 		le128 *wdst;
102 
103 		wsrc = w.src.virt.addr;
104 		wdst = w.dst.virt.addr;
105 
106 		do {
107 			if (unlikely(cts) &&
108 			    w.total - w.nbytes + avail < 2 * XTS_BLOCK_SIZE) {
109 				if (!enc) {
110 					if (second_pass)
111 						rctx->t = t;
112 					gf128mul_x_ble(&t, &t);
113 				}
114 				le128_xor(wdst, &t, wsrc);
115 				if (enc && second_pass)
116 					gf128mul_x_ble(&rctx->t, &t);
117 				skcipher_walk_done(&w, avail - bs);
118 				return 0;
119 			}
120 
121 			le128_xor(wdst++, &t, wsrc++);
122 			gf128mul_x_ble(&t, &t);
123 		} while ((avail -= bs) >= bs);
124 
125 		err = skcipher_walk_done(&w, avail);
126 	}
127 
128 	return err;
129 }
130 
131 static int xor_tweak_pre(struct skcipher_request *req, bool enc)
132 {
133 	return xor_tweak(req, false, enc);
134 }
135 
136 static int xor_tweak_post(struct skcipher_request *req, bool enc)
137 {
138 	return xor_tweak(req, true, enc);
139 }
140 
141 static void cts_done(struct crypto_async_request *areq, int err)
142 {
143 	struct skcipher_request *req = areq->data;
144 	le128 b;
145 
146 	if (!err) {
147 		struct rctx *rctx = skcipher_request_ctx(req);
148 
149 		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
150 		le128_xor(&b, &rctx->t, &b);
151 		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
152 	}
153 
154 	skcipher_request_complete(req, err);
155 }
156 
157 static int cts_final(struct skcipher_request *req,
158 		     int (*crypt)(struct skcipher_request *req))
159 {
160 	struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
161 	int offset = req->cryptlen & ~(XTS_BLOCK_SIZE - 1);
162 	struct rctx *rctx = skcipher_request_ctx(req);
163 	struct skcipher_request *subreq = &rctx->subreq;
164 	int tail = req->cryptlen % XTS_BLOCK_SIZE;
165 	le128 b[2];
166 	int err;
167 
168 	rctx->tail = scatterwalk_ffwd(rctx->sg, req->dst,
169 				      offset - XTS_BLOCK_SIZE);
170 
171 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
172 	memcpy(b + 1, b, tail);
173 	scatterwalk_map_and_copy(b, req->src, offset, tail, 0);
174 
175 	le128_xor(b, &rctx->t, b);
176 
177 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE + tail, 1);
178 
179 	skcipher_request_set_tfm(subreq, ctx->child);
180 	skcipher_request_set_callback(subreq, req->base.flags, cts_done, req);
181 	skcipher_request_set_crypt(subreq, rctx->tail, rctx->tail,
182 				   XTS_BLOCK_SIZE, NULL);
183 
184 	err = crypt(subreq);
185 	if (err)
186 		return err;
187 
188 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
189 	le128_xor(b, &rctx->t, b);
190 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
191 
192 	return 0;
193 }
194 
195 static void encrypt_done(struct crypto_async_request *areq, int err)
196 {
197 	struct skcipher_request *req = areq->data;
198 
199 	if (!err) {
200 		struct rctx *rctx = skcipher_request_ctx(req);
201 
202 		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
203 		err = xor_tweak_post(req, true);
204 
205 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
206 			err = cts_final(req, crypto_skcipher_encrypt);
207 			if (err == -EINPROGRESS)
208 				return;
209 		}
210 	}
211 
212 	skcipher_request_complete(req, err);
213 }
214 
215 static void decrypt_done(struct crypto_async_request *areq, int err)
216 {
217 	struct skcipher_request *req = areq->data;
218 
219 	if (!err) {
220 		struct rctx *rctx = skcipher_request_ctx(req);
221 
222 		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
223 		err = xor_tweak_post(req, false);
224 
225 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
226 			err = cts_final(req, crypto_skcipher_decrypt);
227 			if (err == -EINPROGRESS)
228 				return;
229 		}
230 	}
231 
232 	skcipher_request_complete(req, err);
233 }
234 
235 static int init_crypt(struct skcipher_request *req, crypto_completion_t compl)
236 {
237 	struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
238 	struct rctx *rctx = skcipher_request_ctx(req);
239 	struct skcipher_request *subreq = &rctx->subreq;
240 
241 	if (req->cryptlen < XTS_BLOCK_SIZE)
242 		return -EINVAL;
243 
244 	skcipher_request_set_tfm(subreq, ctx->child);
245 	skcipher_request_set_callback(subreq, req->base.flags, compl, req);
246 	skcipher_request_set_crypt(subreq, req->dst, req->dst,
247 				   req->cryptlen & ~(XTS_BLOCK_SIZE - 1), NULL);
248 
249 	/* calculate first value of T */
250 	crypto_cipher_encrypt_one(ctx->tweak, (u8 *)&rctx->t, req->iv);
251 
252 	return 0;
253 }
254 
255 static int encrypt(struct skcipher_request *req)
256 {
257 	struct rctx *rctx = skcipher_request_ctx(req);
258 	struct skcipher_request *subreq = &rctx->subreq;
259 	int err;
260 
261 	err = init_crypt(req, encrypt_done) ?:
262 	      xor_tweak_pre(req, true) ?:
263 	      crypto_skcipher_encrypt(subreq) ?:
264 	      xor_tweak_post(req, true);
265 
266 	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
267 		return err;
268 
269 	return cts_final(req, crypto_skcipher_encrypt);
270 }
271 
272 static int decrypt(struct skcipher_request *req)
273 {
274 	struct rctx *rctx = skcipher_request_ctx(req);
275 	struct skcipher_request *subreq = &rctx->subreq;
276 	int err;
277 
278 	err = init_crypt(req, decrypt_done) ?:
279 	      xor_tweak_pre(req, false) ?:
280 	      crypto_skcipher_decrypt(subreq) ?:
281 	      xor_tweak_post(req, false);
282 
283 	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
284 		return err;
285 
286 	return cts_final(req, crypto_skcipher_decrypt);
287 }
288 
289 static int init_tfm(struct crypto_skcipher *tfm)
290 {
291 	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
292 	struct xts_instance_ctx *ictx = skcipher_instance_ctx(inst);
293 	struct priv *ctx = crypto_skcipher_ctx(tfm);
294 	struct crypto_skcipher *child;
295 	struct crypto_cipher *tweak;
296 
297 	child = crypto_spawn_skcipher(&ictx->spawn);
298 	if (IS_ERR(child))
299 		return PTR_ERR(child);
300 
301 	ctx->child = child;
302 
303 	tweak = crypto_alloc_cipher(ictx->name, 0, 0);
304 	if (IS_ERR(tweak)) {
305 		crypto_free_skcipher(ctx->child);
306 		return PTR_ERR(tweak);
307 	}
308 
309 	ctx->tweak = tweak;
310 
311 	crypto_skcipher_set_reqsize(tfm, crypto_skcipher_reqsize(child) +
312 					 sizeof(struct rctx));
313 
314 	return 0;
315 }
316 
317 static void exit_tfm(struct crypto_skcipher *tfm)
318 {
319 	struct priv *ctx = crypto_skcipher_ctx(tfm);
320 
321 	crypto_free_skcipher(ctx->child);
322 	crypto_free_cipher(ctx->tweak);
323 }
324 
325 static void free(struct skcipher_instance *inst)
326 {
327 	crypto_drop_skcipher(skcipher_instance_ctx(inst));
328 	kfree(inst);
329 }
330 
331 static int create(struct crypto_template *tmpl, struct rtattr **tb)
332 {
333 	struct skcipher_instance *inst;
334 	struct crypto_attr_type *algt;
335 	struct xts_instance_ctx *ctx;
336 	struct skcipher_alg *alg;
337 	const char *cipher_name;
338 	u32 mask;
339 	int err;
340 
341 	algt = crypto_get_attr_type(tb);
342 	if (IS_ERR(algt))
343 		return PTR_ERR(algt);
344 
345 	if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
346 		return -EINVAL;
347 
348 	cipher_name = crypto_attr_alg_name(tb[1]);
349 	if (IS_ERR(cipher_name))
350 		return PTR_ERR(cipher_name);
351 
352 	inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
353 	if (!inst)
354 		return -ENOMEM;
355 
356 	ctx = skcipher_instance_ctx(inst);
357 
358 	mask = crypto_requires_off(algt->type, algt->mask,
359 				   CRYPTO_ALG_NEED_FALLBACK |
360 				   CRYPTO_ALG_ASYNC);
361 
362 	err = crypto_grab_skcipher(&ctx->spawn, skcipher_crypto_instance(inst),
363 				   cipher_name, 0, mask);
364 	if (err == -ENOENT) {
365 		err = -ENAMETOOLONG;
366 		if (snprintf(ctx->name, CRYPTO_MAX_ALG_NAME, "ecb(%s)",
367 			     cipher_name) >= CRYPTO_MAX_ALG_NAME)
368 			goto err_free_inst;
369 
370 		err = crypto_grab_skcipher(&ctx->spawn,
371 					   skcipher_crypto_instance(inst),
372 					   ctx->name, 0, mask);
373 	}
374 
375 	if (err)
376 		goto err_free_inst;
377 
378 	alg = crypto_skcipher_spawn_alg(&ctx->spawn);
379 
380 	err = -EINVAL;
381 	if (alg->base.cra_blocksize != XTS_BLOCK_SIZE)
382 		goto err_drop_spawn;
383 
384 	if (crypto_skcipher_alg_ivsize(alg))
385 		goto err_drop_spawn;
386 
387 	err = crypto_inst_setname(skcipher_crypto_instance(inst), "xts",
388 				  &alg->base);
389 	if (err)
390 		goto err_drop_spawn;
391 
392 	err = -EINVAL;
393 	cipher_name = alg->base.cra_name;
394 
395 	/* Alas we screwed up the naming so we have to mangle the
396 	 * cipher name.
397 	 */
398 	if (!strncmp(cipher_name, "ecb(", 4)) {
399 		unsigned len;
400 
401 		len = strlcpy(ctx->name, cipher_name + 4, sizeof(ctx->name));
402 		if (len < 2 || len >= sizeof(ctx->name))
403 			goto err_drop_spawn;
404 
405 		if (ctx->name[len - 1] != ')')
406 			goto err_drop_spawn;
407 
408 		ctx->name[len - 1] = 0;
409 
410 		if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
411 			     "xts(%s)", ctx->name) >= CRYPTO_MAX_ALG_NAME) {
412 			err = -ENAMETOOLONG;
413 			goto err_drop_spawn;
414 		}
415 	} else
416 		goto err_drop_spawn;
417 
418 	inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
419 	inst->alg.base.cra_priority = alg->base.cra_priority;
420 	inst->alg.base.cra_blocksize = XTS_BLOCK_SIZE;
421 	inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
422 				       (__alignof__(u64) - 1);
423 
424 	inst->alg.ivsize = XTS_BLOCK_SIZE;
425 	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) * 2;
426 	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) * 2;
427 
428 	inst->alg.base.cra_ctxsize = sizeof(struct priv);
429 
430 	inst->alg.init = init_tfm;
431 	inst->alg.exit = exit_tfm;
432 
433 	inst->alg.setkey = setkey;
434 	inst->alg.encrypt = encrypt;
435 	inst->alg.decrypt = decrypt;
436 
437 	inst->free = free;
438 
439 	err = skcipher_register_instance(tmpl, inst);
440 	if (err)
441 		goto err_drop_spawn;
442 
443 out:
444 	return err;
445 
446 err_drop_spawn:
447 	crypto_drop_skcipher(&ctx->spawn);
448 err_free_inst:
449 	kfree(inst);
450 	goto out;
451 }
452 
453 static struct crypto_template crypto_tmpl = {
454 	.name = "xts",
455 	.create = create,
456 	.module = THIS_MODULE,
457 };
458 
459 static int __init crypto_module_init(void)
460 {
461 	return crypto_register_template(&crypto_tmpl);
462 }
463 
464 static void __exit crypto_module_exit(void)
465 {
466 	crypto_unregister_template(&crypto_tmpl);
467 }
468 
469 subsys_initcall(crypto_module_init);
470 module_exit(crypto_module_exit);
471 
472 MODULE_LICENSE("GPL");
473 MODULE_DESCRIPTION("XTS block cipher mode");
474 MODULE_ALIAS_CRYPTO("xts");
475