xref: /openbmc/linux/crypto/xts.c (revision c4c3c32d) 
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/cipher.h>
11 #include <crypto/internal/skcipher.h>
12 #include <crypto/scatterwalk.h>
13 #include <linux/err.h>
14 #include <linux/init.h>
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/scatterlist.h>
18 #include <linux/slab.h>
19 
20 #include <crypto/xts.h>
21 #include <crypto/b128ops.h>
22 #include <crypto/gf128mul.h>
23 
24 struct xts_tfm_ctx {
25 	struct crypto_skcipher *child;
26 	struct crypto_cipher *tweak;
27 };
28 
29 struct xts_instance_ctx {
30 	struct crypto_skcipher_spawn spawn;
31 	char name[CRYPTO_MAX_ALG_NAME];
32 };
33 
34 struct xts_request_ctx {
35 	le128 t;
36 	struct scatterlist *tail;
37 	struct scatterlist sg[2];
38 	struct skcipher_request subreq;
39 };
40 
41 static int xts_setkey(struct crypto_skcipher *parent, const u8 *key,
42 		      unsigned int keylen)
43 {
44 	struct xts_tfm_ctx *ctx = crypto_skcipher_ctx(parent);
45 	struct crypto_skcipher *child;
46 	struct crypto_cipher *tweak;
47 	int err;
48 
49 	err = xts_verify_key(parent, key, keylen);
50 	if (err)
51 		return err;
52 
53 	keylen /= 2;
54 
55 	/* we need two cipher instances: one to compute the initial 'tweak'
56 	 * by encrypting the IV (usually the 'plain' iv) and the other
57 	 * one to encrypt and decrypt the data */
58 
59 	/* tweak cipher, uses Key2 i.e. the second half of *key */
60 	tweak = ctx->tweak;
61 	crypto_cipher_clear_flags(tweak, CRYPTO_TFM_REQ_MASK);
62 	crypto_cipher_set_flags(tweak, crypto_skcipher_get_flags(parent) &
63 				       CRYPTO_TFM_REQ_MASK);
64 	err = crypto_cipher_setkey(tweak, key + keylen, keylen);
65 	if (err)
66 		return err;
67 
68 	/* data cipher, uses Key1 i.e. the first half of *key */
69 	child = ctx->child;
70 	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
71 	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
72 					 CRYPTO_TFM_REQ_MASK);
73 	return crypto_skcipher_setkey(child, key, keylen);
74 }
75 
76 /*
77  * We compute the tweak masks twice (both before and after the ECB encryption or
78  * decryption) to avoid having to allocate a temporary buffer and/or make
79  * mutliple calls to the 'ecb(..)' instance, which usually would be slower than
80  * just doing the gf128mul_x_ble() calls again.
81  */
82 static int xts_xor_tweak(struct skcipher_request *req, bool second_pass,
83 			 bool enc)
84 {
85 	struct xts_request_ctx *rctx = skcipher_request_ctx(req);
86 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
87 	const bool cts = (req->cryptlen % XTS_BLOCK_SIZE);
88 	const int bs = XTS_BLOCK_SIZE;
89 	struct skcipher_walk w;
90 	le128 t = rctx->t;
91 	int err;
92 
93 	if (second_pass) {
94 		req = &rctx->subreq;
95 		/* set to our TFM to enforce correct alignment: */
96 		skcipher_request_set_tfm(req, tfm);
97 	}
98 	err = skcipher_walk_virt(&w, req, false);
99 
100 	while (w.nbytes) {
101 		unsigned int avail = w.nbytes;
102 		le128 *wsrc;
103 		le128 *wdst;
104 
105 		wsrc = w.src.virt.addr;
106 		wdst = w.dst.virt.addr;
107 
108 		do {
109 			if (unlikely(cts) &&
110 			    w.total - w.nbytes + avail < 2 * XTS_BLOCK_SIZE) {
111 				if (!enc) {
112 					if (second_pass)
113 						rctx->t = t;
114 					gf128mul_x_ble(&t, &t);
115 				}
116 				le128_xor(wdst, &t, wsrc);
117 				if (enc && second_pass)
118 					gf128mul_x_ble(&rctx->t, &t);
119 				skcipher_walk_done(&w, avail - bs);
120 				return 0;
121 			}
122 
123 			le128_xor(wdst++, &t, wsrc++);
124 			gf128mul_x_ble(&t, &t);
125 		} while ((avail -= bs) >= bs);
126 
127 		err = skcipher_walk_done(&w, avail);
128 	}
129 
130 	return err;
131 }
132 
133 static int xts_xor_tweak_pre(struct skcipher_request *req, bool enc)
134 {
135 	return xts_xor_tweak(req, false, enc);
136 }
137 
138 static int xts_xor_tweak_post(struct skcipher_request *req, bool enc)
139 {
140 	return xts_xor_tweak(req, true, enc);
141 }
142 
143 static void xts_cts_done(void *data, int err)
144 {
145 	struct skcipher_request *req = data;
146 	le128 b;
147 
148 	if (!err) {
149 		struct xts_request_ctx *rctx = skcipher_request_ctx(req);
150 
151 		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
152 		le128_xor(&b, &rctx->t, &b);
153 		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
154 	}
155 
156 	skcipher_request_complete(req, err);
157 }
158 
159 static int xts_cts_final(struct skcipher_request *req,
160 			 int (*crypt)(struct skcipher_request *req))
161 {
162 	const struct xts_tfm_ctx *ctx =
163 		crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
164 	int offset = req->cryptlen & ~(XTS_BLOCK_SIZE - 1);
165 	struct xts_request_ctx *rctx = skcipher_request_ctx(req);
166 	struct skcipher_request *subreq = &rctx->subreq;
167 	int tail = req->cryptlen % XTS_BLOCK_SIZE;
168 	le128 b[2];
169 	int err;
170 
171 	rctx->tail = scatterwalk_ffwd(rctx->sg, req->dst,
172 				      offset - XTS_BLOCK_SIZE);
173 
174 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
175 	b[1] = b[0];
176 	scatterwalk_map_and_copy(b, req->src, offset, tail, 0);
177 
178 	le128_xor(b, &rctx->t, b);
179 
180 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE + tail, 1);
181 
182 	skcipher_request_set_tfm(subreq, ctx->child);
183 	skcipher_request_set_callback(subreq, req->base.flags, xts_cts_done,
184 				      req);
185 	skcipher_request_set_crypt(subreq, rctx->tail, rctx->tail,
186 				   XTS_BLOCK_SIZE, NULL);
187 
188 	err = crypt(subreq);
189 	if (err)
190 		return err;
191 
192 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
193 	le128_xor(b, &rctx->t, b);
194 	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
195 
196 	return 0;
197 }
198 
199 static void xts_encrypt_done(void *data, int err)
200 {
201 	struct skcipher_request *req = data;
202 
203 	if (!err) {
204 		struct xts_request_ctx *rctx = skcipher_request_ctx(req);
205 
206 		rctx->subreq.base.flags &= CRYPTO_TFM_REQ_MAY_BACKLOG;
207 		err = xts_xor_tweak_post(req, true);
208 
209 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
210 			err = xts_cts_final(req, crypto_skcipher_encrypt);
211 			if (err == -EINPROGRESS || err == -EBUSY)
212 				return;
213 		}
214 	}
215 
216 	skcipher_request_complete(req, err);
217 }
218 
219 static void xts_decrypt_done(void *data, int err)
220 {
221 	struct skcipher_request *req = data;
222 
223 	if (!err) {
224 		struct xts_request_ctx *rctx = skcipher_request_ctx(req);
225 
226 		rctx->subreq.base.flags &= CRYPTO_TFM_REQ_MAY_BACKLOG;
227 		err = xts_xor_tweak_post(req, false);
228 
229 		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
230 			err = xts_cts_final(req, crypto_skcipher_decrypt);
231 			if (err == -EINPROGRESS || err == -EBUSY)
232 				return;
233 		}
234 	}
235 
236 	skcipher_request_complete(req, err);
237 }
238 
239 static int xts_init_crypt(struct skcipher_request *req,
240 			  crypto_completion_t compl)
241 {
242 	const struct xts_tfm_ctx *ctx =
243 		crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
244 	struct xts_request_ctx *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 xts_encrypt(struct skcipher_request *req)
262 {
263 	struct xts_request_ctx *rctx = skcipher_request_ctx(req);
264 	struct skcipher_request *subreq = &rctx->subreq;
265 	int err;
266 
267 	err = xts_init_crypt(req, xts_encrypt_done) ?:
268 	      xts_xor_tweak_pre(req, true) ?:
269 	      crypto_skcipher_encrypt(subreq) ?:
270 	      xts_xor_tweak_post(req, true);
271 
272 	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
273 		return err;
274 
275 	return xts_cts_final(req, crypto_skcipher_encrypt);
276 }
277 
278 static int xts_decrypt(struct skcipher_request *req)
279 {
280 	struct xts_request_ctx *rctx = skcipher_request_ctx(req);
281 	struct skcipher_request *subreq = &rctx->subreq;
282 	int err;
283 
284 	err = xts_init_crypt(req, xts_decrypt_done) ?:
285 	      xts_xor_tweak_pre(req, false) ?:
286 	      crypto_skcipher_decrypt(subreq) ?:
287 	      xts_xor_tweak_post(req, false);
288 
289 	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
290 		return err;
291 
292 	return xts_cts_final(req, crypto_skcipher_decrypt);
293 }
294 
295 static int xts_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 xts_tfm_ctx *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 xts_request_ctx));
319 
320 	return 0;
321 }
322 
323 static void xts_exit_tfm(struct crypto_skcipher *tfm)
324 {
325 	struct xts_tfm_ctx *ctx = crypto_skcipher_ctx(tfm);
326 
327 	crypto_free_skcipher(ctx->child);
328 	crypto_free_cipher(ctx->tweak);
329 }
330 
331 static void xts_free_instance(struct skcipher_instance *inst)
332 {
333 	struct xts_instance_ctx *ictx = skcipher_instance_ctx(inst);
334 
335 	crypto_drop_skcipher(&ictx->spawn);
336 	kfree(inst);
337 }
338 
339 static int xts_create(struct crypto_template *tmpl, struct rtattr **tb)
340 {
341 	struct skcipher_instance *inst;
342 	struct xts_instance_ctx *ctx;
343 	struct skcipher_alg *alg;
344 	const char *cipher_name;
345 	u32 mask;
346 	int err;
347 
348 	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER, &mask);
349 	if (err)
350 		return err;
351 
352 	cipher_name = crypto_attr_alg_name(tb[1]);
353 	if (IS_ERR(cipher_name))
354 		return PTR_ERR(cipher_name);
355 
356 	inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
357 	if (!inst)
358 		return -ENOMEM;
359 
360 	ctx = skcipher_instance_ctx(inst);
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_free_inst;
383 
384 	if (crypto_skcipher_alg_ivsize(alg))
385 		goto err_free_inst;
386 
387 	err = crypto_inst_setname(skcipher_crypto_instance(inst), "xts",
388 				  &alg->base);
389 	if (err)
390 		goto err_free_inst;
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_free_inst;
404 
405 		if (ctx->name[len - 1] != ')')
406 			goto err_free_inst;
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_free_inst;
414 		}
415 	} else
416 		goto err_free_inst;
417 
418 	inst->alg.base.cra_priority = alg->base.cra_priority;
419 	inst->alg.base.cra_blocksize = XTS_BLOCK_SIZE;
420 	inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
421 				       (__alignof__(u64) - 1);
422 
423 	inst->alg.ivsize = XTS_BLOCK_SIZE;
424 	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) * 2;
425 	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) * 2;
426 
427 	inst->alg.base.cra_ctxsize = sizeof(struct xts_tfm_ctx);
428 
429 	inst->alg.init = xts_init_tfm;
430 	inst->alg.exit = xts_exit_tfm;
431 
432 	inst->alg.setkey = xts_setkey;
433 	inst->alg.encrypt = xts_encrypt;
434 	inst->alg.decrypt = xts_decrypt;
435 
436 	inst->free = xts_free_instance;
437 
438 	err = skcipher_register_instance(tmpl, inst);
439 	if (err) {
440 err_free_inst:
441 		xts_free_instance(inst);
442 	}
443 	return err;
444 }
445 
446 static struct crypto_template xts_tmpl = {
447 	.name = "xts",
448 	.create = xts_create,
449 	.module = THIS_MODULE,
450 };
451 
452 static int __init xts_module_init(void)
453 {
454 	return crypto_register_template(&xts_tmpl);
455 }
456 
457 static void __exit xts_module_exit(void)
458 {
459 	crypto_unregister_template(&xts_tmpl);
460 }
461 
462 subsys_initcall(xts_module_init);
463 module_exit(xts_module_exit);
464 
465 MODULE_LICENSE("GPL");
466 MODULE_DESCRIPTION("XTS block cipher mode");
467 MODULE_ALIAS_CRYPTO("xts");
468 MODULE_IMPORT_NS(CRYPTO_INTERNAL);
469 MODULE_SOFTDEP("pre: ecb");
470