xref: /openbmc/linux/block/blk-crypto-fallback.c (revision 08b7cf13)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Copyright 2019 Google LLC
4  */
5 
6 /*
7  * Refer to Documentation/block/inline-encryption.rst for detailed explanation.
8  */
9 
10 #define pr_fmt(fmt) "blk-crypto-fallback: " fmt
11 
12 #include <crypto/skcipher.h>
13 #include <linux/blk-crypto.h>
14 #include <linux/blk-crypto-profile.h>
15 #include <linux/blkdev.h>
16 #include <linux/crypto.h>
17 #include <linux/mempool.h>
18 #include <linux/module.h>
19 #include <linux/random.h>
20 #include <linux/scatterlist.h>
21 
22 #include "blk-cgroup.h"
23 #include "blk-crypto-internal.h"
24 
25 static unsigned int num_prealloc_bounce_pg = 32;
26 module_param(num_prealloc_bounce_pg, uint, 0);
27 MODULE_PARM_DESC(num_prealloc_bounce_pg,
28 		 "Number of preallocated bounce pages for the blk-crypto crypto API fallback");
29 
30 static unsigned int blk_crypto_num_keyslots = 100;
31 module_param_named(num_keyslots, blk_crypto_num_keyslots, uint, 0);
32 MODULE_PARM_DESC(num_keyslots,
33 		 "Number of keyslots for the blk-crypto crypto API fallback");
34 
35 static unsigned int num_prealloc_fallback_crypt_ctxs = 128;
36 module_param(num_prealloc_fallback_crypt_ctxs, uint, 0);
37 MODULE_PARM_DESC(num_prealloc_crypt_fallback_ctxs,
38 		 "Number of preallocated bio fallback crypto contexts for blk-crypto to use during crypto API fallback");
39 
40 struct bio_fallback_crypt_ctx {
41 	struct bio_crypt_ctx crypt_ctx;
42 	/*
43 	 * Copy of the bvec_iter when this bio was submitted.
44 	 * We only want to en/decrypt the part of the bio as described by the
45 	 * bvec_iter upon submission because bio might be split before being
46 	 * resubmitted
47 	 */
48 	struct bvec_iter crypt_iter;
49 	union {
50 		struct {
51 			struct work_struct work;
52 			struct bio *bio;
53 		};
54 		struct {
55 			void *bi_private_orig;
56 			bio_end_io_t *bi_end_io_orig;
57 		};
58 	};
59 };
60 
61 static struct kmem_cache *bio_fallback_crypt_ctx_cache;
62 static mempool_t *bio_fallback_crypt_ctx_pool;
63 
64 /*
65  * Allocating a crypto tfm during I/O can deadlock, so we have to preallocate
66  * all of a mode's tfms when that mode starts being used. Since each mode may
67  * need all the keyslots at some point, each mode needs its own tfm for each
68  * keyslot; thus, a keyslot may contain tfms for multiple modes.  However, to
69  * match the behavior of real inline encryption hardware (which only supports a
70  * single encryption context per keyslot), we only allow one tfm per keyslot to
71  * be used at a time - the rest of the unused tfms have their keys cleared.
72  */
73 static DEFINE_MUTEX(tfms_init_lock);
74 static bool tfms_inited[BLK_ENCRYPTION_MODE_MAX];
75 
76 static struct blk_crypto_fallback_keyslot {
77 	enum blk_crypto_mode_num crypto_mode;
78 	struct crypto_skcipher *tfms[BLK_ENCRYPTION_MODE_MAX];
79 } *blk_crypto_keyslots;
80 
81 static struct blk_crypto_profile blk_crypto_fallback_profile;
82 static struct workqueue_struct *blk_crypto_wq;
83 static mempool_t *blk_crypto_bounce_page_pool;
84 static struct bio_set crypto_bio_split;
85 
86 /*
87  * This is the key we set when evicting a keyslot. This *should* be the all 0's
88  * key, but AES-XTS rejects that key, so we use some random bytes instead.
89  */
90 static u8 blank_key[BLK_CRYPTO_MAX_KEY_SIZE];
91 
92 static void blk_crypto_fallback_evict_keyslot(unsigned int slot)
93 {
94 	struct blk_crypto_fallback_keyslot *slotp = &blk_crypto_keyslots[slot];
95 	enum blk_crypto_mode_num crypto_mode = slotp->crypto_mode;
96 	int err;
97 
98 	WARN_ON(slotp->crypto_mode == BLK_ENCRYPTION_MODE_INVALID);
99 
100 	/* Clear the key in the skcipher */
101 	err = crypto_skcipher_setkey(slotp->tfms[crypto_mode], blank_key,
102 				     blk_crypto_modes[crypto_mode].keysize);
103 	WARN_ON(err);
104 	slotp->crypto_mode = BLK_ENCRYPTION_MODE_INVALID;
105 }
106 
107 static int
108 blk_crypto_fallback_keyslot_program(struct blk_crypto_profile *profile,
109 				    const struct blk_crypto_key *key,
110 				    unsigned int slot)
111 {
112 	struct blk_crypto_fallback_keyslot *slotp = &blk_crypto_keyslots[slot];
113 	const enum blk_crypto_mode_num crypto_mode =
114 						key->crypto_cfg.crypto_mode;
115 	int err;
116 
117 	if (crypto_mode != slotp->crypto_mode &&
118 	    slotp->crypto_mode != BLK_ENCRYPTION_MODE_INVALID)
119 		blk_crypto_fallback_evict_keyslot(slot);
120 
121 	slotp->crypto_mode = crypto_mode;
122 	err = crypto_skcipher_setkey(slotp->tfms[crypto_mode], key->raw,
123 				     key->size);
124 	if (err) {
125 		blk_crypto_fallback_evict_keyslot(slot);
126 		return err;
127 	}
128 	return 0;
129 }
130 
131 static int blk_crypto_fallback_keyslot_evict(struct blk_crypto_profile *profile,
132 					     const struct blk_crypto_key *key,
133 					     unsigned int slot)
134 {
135 	blk_crypto_fallback_evict_keyslot(slot);
136 	return 0;
137 }
138 
139 static const struct blk_crypto_ll_ops blk_crypto_fallback_ll_ops = {
140 	.keyslot_program        = blk_crypto_fallback_keyslot_program,
141 	.keyslot_evict          = blk_crypto_fallback_keyslot_evict,
142 };
143 
144 static void blk_crypto_fallback_encrypt_endio(struct bio *enc_bio)
145 {
146 	struct bio *src_bio = enc_bio->bi_private;
147 	int i;
148 
149 	for (i = 0; i < enc_bio->bi_vcnt; i++)
150 		mempool_free(enc_bio->bi_io_vec[i].bv_page,
151 			     blk_crypto_bounce_page_pool);
152 
153 	src_bio->bi_status = enc_bio->bi_status;
154 
155 	bio_put(enc_bio);
156 	bio_endio(src_bio);
157 }
158 
159 static struct bio *blk_crypto_fallback_clone_bio(struct bio *bio_src)
160 {
161 	struct bvec_iter iter;
162 	struct bio_vec bv;
163 	struct bio *bio;
164 
165 	bio = bio_kmalloc(GFP_NOIO, bio_segments(bio_src));
166 	if (!bio)
167 		return NULL;
168 	bio->bi_bdev		= bio_src->bi_bdev;
169 	if (bio_flagged(bio_src, BIO_REMAPPED))
170 		bio_set_flag(bio, BIO_REMAPPED);
171 	bio->bi_opf		= bio_src->bi_opf;
172 	bio->bi_ioprio		= bio_src->bi_ioprio;
173 	bio->bi_iter.bi_sector	= bio_src->bi_iter.bi_sector;
174 	bio->bi_iter.bi_size	= bio_src->bi_iter.bi_size;
175 
176 	bio_for_each_segment(bv, bio_src, iter)
177 		bio->bi_io_vec[bio->bi_vcnt++] = bv;
178 
179 	bio_clone_blkg_association(bio, bio_src);
180 	blkcg_bio_issue_init(bio);
181 
182 	return bio;
183 }
184 
185 static bool
186 blk_crypto_fallback_alloc_cipher_req(struct blk_crypto_keyslot *slot,
187 				     struct skcipher_request **ciph_req_ret,
188 				     struct crypto_wait *wait)
189 {
190 	struct skcipher_request *ciph_req;
191 	const struct blk_crypto_fallback_keyslot *slotp;
192 	int keyslot_idx = blk_crypto_keyslot_index(slot);
193 
194 	slotp = &blk_crypto_keyslots[keyslot_idx];
195 	ciph_req = skcipher_request_alloc(slotp->tfms[slotp->crypto_mode],
196 					  GFP_NOIO);
197 	if (!ciph_req)
198 		return false;
199 
200 	skcipher_request_set_callback(ciph_req,
201 				      CRYPTO_TFM_REQ_MAY_BACKLOG |
202 				      CRYPTO_TFM_REQ_MAY_SLEEP,
203 				      crypto_req_done, wait);
204 	*ciph_req_ret = ciph_req;
205 
206 	return true;
207 }
208 
209 static bool blk_crypto_fallback_split_bio_if_needed(struct bio **bio_ptr)
210 {
211 	struct bio *bio = *bio_ptr;
212 	unsigned int i = 0;
213 	unsigned int num_sectors = 0;
214 	struct bio_vec bv;
215 	struct bvec_iter iter;
216 
217 	bio_for_each_segment(bv, bio, iter) {
218 		num_sectors += bv.bv_len >> SECTOR_SHIFT;
219 		if (++i == BIO_MAX_VECS)
220 			break;
221 	}
222 	if (num_sectors < bio_sectors(bio)) {
223 		struct bio *split_bio;
224 
225 		split_bio = bio_split(bio, num_sectors, GFP_NOIO,
226 				      &crypto_bio_split);
227 		if (!split_bio) {
228 			bio->bi_status = BLK_STS_RESOURCE;
229 			return false;
230 		}
231 		bio_chain(split_bio, bio);
232 		submit_bio_noacct(bio);
233 		*bio_ptr = split_bio;
234 	}
235 
236 	return true;
237 }
238 
239 union blk_crypto_iv {
240 	__le64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
241 	u8 bytes[BLK_CRYPTO_MAX_IV_SIZE];
242 };
243 
244 static void blk_crypto_dun_to_iv(const u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE],
245 				 union blk_crypto_iv *iv)
246 {
247 	int i;
248 
249 	for (i = 0; i < BLK_CRYPTO_DUN_ARRAY_SIZE; i++)
250 		iv->dun[i] = cpu_to_le64(dun[i]);
251 }
252 
253 /*
254  * The crypto API fallback's encryption routine.
255  * Allocate a bounce bio for encryption, encrypt the input bio using crypto API,
256  * and replace *bio_ptr with the bounce bio. May split input bio if it's too
257  * large. Returns true on success. Returns false and sets bio->bi_status on
258  * error.
259  */
260 static bool blk_crypto_fallback_encrypt_bio(struct bio **bio_ptr)
261 {
262 	struct bio *src_bio, *enc_bio;
263 	struct bio_crypt_ctx *bc;
264 	struct blk_crypto_keyslot *slot;
265 	int data_unit_size;
266 	struct skcipher_request *ciph_req = NULL;
267 	DECLARE_CRYPTO_WAIT(wait);
268 	u64 curr_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
269 	struct scatterlist src, dst;
270 	union blk_crypto_iv iv;
271 	unsigned int i, j;
272 	bool ret = false;
273 	blk_status_t blk_st;
274 
275 	/* Split the bio if it's too big for single page bvec */
276 	if (!blk_crypto_fallback_split_bio_if_needed(bio_ptr))
277 		return false;
278 
279 	src_bio = *bio_ptr;
280 	bc = src_bio->bi_crypt_context;
281 	data_unit_size = bc->bc_key->crypto_cfg.data_unit_size;
282 
283 	/* Allocate bounce bio for encryption */
284 	enc_bio = blk_crypto_fallback_clone_bio(src_bio);
285 	if (!enc_bio) {
286 		src_bio->bi_status = BLK_STS_RESOURCE;
287 		return false;
288 	}
289 
290 	/*
291 	 * Get a blk-crypto-fallback keyslot that contains a crypto_skcipher for
292 	 * this bio's algorithm and key.
293 	 */
294 	blk_st = blk_crypto_get_keyslot(&blk_crypto_fallback_profile,
295 					bc->bc_key, &slot);
296 	if (blk_st != BLK_STS_OK) {
297 		src_bio->bi_status = blk_st;
298 		goto out_put_enc_bio;
299 	}
300 
301 	/* and then allocate an skcipher_request for it */
302 	if (!blk_crypto_fallback_alloc_cipher_req(slot, &ciph_req, &wait)) {
303 		src_bio->bi_status = BLK_STS_RESOURCE;
304 		goto out_release_keyslot;
305 	}
306 
307 	memcpy(curr_dun, bc->bc_dun, sizeof(curr_dun));
308 	sg_init_table(&src, 1);
309 	sg_init_table(&dst, 1);
310 
311 	skcipher_request_set_crypt(ciph_req, &src, &dst, data_unit_size,
312 				   iv.bytes);
313 
314 	/* Encrypt each page in the bounce bio */
315 	for (i = 0; i < enc_bio->bi_vcnt; i++) {
316 		struct bio_vec *enc_bvec = &enc_bio->bi_io_vec[i];
317 		struct page *plaintext_page = enc_bvec->bv_page;
318 		struct page *ciphertext_page =
319 			mempool_alloc(blk_crypto_bounce_page_pool, GFP_NOIO);
320 
321 		enc_bvec->bv_page = ciphertext_page;
322 
323 		if (!ciphertext_page) {
324 			src_bio->bi_status = BLK_STS_RESOURCE;
325 			goto out_free_bounce_pages;
326 		}
327 
328 		sg_set_page(&src, plaintext_page, data_unit_size,
329 			    enc_bvec->bv_offset);
330 		sg_set_page(&dst, ciphertext_page, data_unit_size,
331 			    enc_bvec->bv_offset);
332 
333 		/* Encrypt each data unit in this page */
334 		for (j = 0; j < enc_bvec->bv_len; j += data_unit_size) {
335 			blk_crypto_dun_to_iv(curr_dun, &iv);
336 			if (crypto_wait_req(crypto_skcipher_encrypt(ciph_req),
337 					    &wait)) {
338 				i++;
339 				src_bio->bi_status = BLK_STS_IOERR;
340 				goto out_free_bounce_pages;
341 			}
342 			bio_crypt_dun_increment(curr_dun, 1);
343 			src.offset += data_unit_size;
344 			dst.offset += data_unit_size;
345 		}
346 	}
347 
348 	enc_bio->bi_private = src_bio;
349 	enc_bio->bi_end_io = blk_crypto_fallback_encrypt_endio;
350 	*bio_ptr = enc_bio;
351 	ret = true;
352 
353 	enc_bio = NULL;
354 	goto out_free_ciph_req;
355 
356 out_free_bounce_pages:
357 	while (i > 0)
358 		mempool_free(enc_bio->bi_io_vec[--i].bv_page,
359 			     blk_crypto_bounce_page_pool);
360 out_free_ciph_req:
361 	skcipher_request_free(ciph_req);
362 out_release_keyslot:
363 	blk_crypto_put_keyslot(slot);
364 out_put_enc_bio:
365 	if (enc_bio)
366 		bio_put(enc_bio);
367 
368 	return ret;
369 }
370 
371 /*
372  * The crypto API fallback's main decryption routine.
373  * Decrypts input bio in place, and calls bio_endio on the bio.
374  */
375 static void blk_crypto_fallback_decrypt_bio(struct work_struct *work)
376 {
377 	struct bio_fallback_crypt_ctx *f_ctx =
378 		container_of(work, struct bio_fallback_crypt_ctx, work);
379 	struct bio *bio = f_ctx->bio;
380 	struct bio_crypt_ctx *bc = &f_ctx->crypt_ctx;
381 	struct blk_crypto_keyslot *slot;
382 	struct skcipher_request *ciph_req = NULL;
383 	DECLARE_CRYPTO_WAIT(wait);
384 	u64 curr_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
385 	union blk_crypto_iv iv;
386 	struct scatterlist sg;
387 	struct bio_vec bv;
388 	struct bvec_iter iter;
389 	const int data_unit_size = bc->bc_key->crypto_cfg.data_unit_size;
390 	unsigned int i;
391 	blk_status_t blk_st;
392 
393 	/*
394 	 * Get a blk-crypto-fallback keyslot that contains a crypto_skcipher for
395 	 * this bio's algorithm and key.
396 	 */
397 	blk_st = blk_crypto_get_keyslot(&blk_crypto_fallback_profile,
398 					bc->bc_key, &slot);
399 	if (blk_st != BLK_STS_OK) {
400 		bio->bi_status = blk_st;
401 		goto out_no_keyslot;
402 	}
403 
404 	/* and then allocate an skcipher_request for it */
405 	if (!blk_crypto_fallback_alloc_cipher_req(slot, &ciph_req, &wait)) {
406 		bio->bi_status = BLK_STS_RESOURCE;
407 		goto out;
408 	}
409 
410 	memcpy(curr_dun, bc->bc_dun, sizeof(curr_dun));
411 	sg_init_table(&sg, 1);
412 	skcipher_request_set_crypt(ciph_req, &sg, &sg, data_unit_size,
413 				   iv.bytes);
414 
415 	/* Decrypt each segment in the bio */
416 	__bio_for_each_segment(bv, bio, iter, f_ctx->crypt_iter) {
417 		struct page *page = bv.bv_page;
418 
419 		sg_set_page(&sg, page, data_unit_size, bv.bv_offset);
420 
421 		/* Decrypt each data unit in the segment */
422 		for (i = 0; i < bv.bv_len; i += data_unit_size) {
423 			blk_crypto_dun_to_iv(curr_dun, &iv);
424 			if (crypto_wait_req(crypto_skcipher_decrypt(ciph_req),
425 					    &wait)) {
426 				bio->bi_status = BLK_STS_IOERR;
427 				goto out;
428 			}
429 			bio_crypt_dun_increment(curr_dun, 1);
430 			sg.offset += data_unit_size;
431 		}
432 	}
433 
434 out:
435 	skcipher_request_free(ciph_req);
436 	blk_crypto_put_keyslot(slot);
437 out_no_keyslot:
438 	mempool_free(f_ctx, bio_fallback_crypt_ctx_pool);
439 	bio_endio(bio);
440 }
441 
442 /**
443  * blk_crypto_fallback_decrypt_endio - queue bio for fallback decryption
444  *
445  * @bio: the bio to queue
446  *
447  * Restore bi_private and bi_end_io, and queue the bio for decryption into a
448  * workqueue, since this function will be called from an atomic context.
449  */
450 static void blk_crypto_fallback_decrypt_endio(struct bio *bio)
451 {
452 	struct bio_fallback_crypt_ctx *f_ctx = bio->bi_private;
453 
454 	bio->bi_private = f_ctx->bi_private_orig;
455 	bio->bi_end_io = f_ctx->bi_end_io_orig;
456 
457 	/* If there was an IO error, don't queue for decrypt. */
458 	if (bio->bi_status) {
459 		mempool_free(f_ctx, bio_fallback_crypt_ctx_pool);
460 		bio_endio(bio);
461 		return;
462 	}
463 
464 	INIT_WORK(&f_ctx->work, blk_crypto_fallback_decrypt_bio);
465 	f_ctx->bio = bio;
466 	queue_work(blk_crypto_wq, &f_ctx->work);
467 }
468 
469 /**
470  * blk_crypto_fallback_bio_prep - Prepare a bio to use fallback en/decryption
471  *
472  * @bio_ptr: pointer to the bio to prepare
473  *
474  * If bio is doing a WRITE operation, this splits the bio into two parts if it's
475  * too big (see blk_crypto_fallback_split_bio_if_needed()). It then allocates a
476  * bounce bio for the first part, encrypts it, and updates bio_ptr to point to
477  * the bounce bio.
478  *
479  * For a READ operation, we mark the bio for decryption by using bi_private and
480  * bi_end_io.
481  *
482  * In either case, this function will make the bio look like a regular bio (i.e.
483  * as if no encryption context was ever specified) for the purposes of the rest
484  * of the stack except for blk-integrity (blk-integrity and blk-crypto are not
485  * currently supported together).
486  *
487  * Return: true on success. Sets bio->bi_status and returns false on error.
488  */
489 bool blk_crypto_fallback_bio_prep(struct bio **bio_ptr)
490 {
491 	struct bio *bio = *bio_ptr;
492 	struct bio_crypt_ctx *bc = bio->bi_crypt_context;
493 	struct bio_fallback_crypt_ctx *f_ctx;
494 
495 	if (WARN_ON_ONCE(!tfms_inited[bc->bc_key->crypto_cfg.crypto_mode])) {
496 		/* User didn't call blk_crypto_start_using_key() first */
497 		bio->bi_status = BLK_STS_IOERR;
498 		return false;
499 	}
500 
501 	if (!__blk_crypto_cfg_supported(&blk_crypto_fallback_profile,
502 					&bc->bc_key->crypto_cfg)) {
503 		bio->bi_status = BLK_STS_NOTSUPP;
504 		return false;
505 	}
506 
507 	if (bio_data_dir(bio) == WRITE)
508 		return blk_crypto_fallback_encrypt_bio(bio_ptr);
509 
510 	/*
511 	 * bio READ case: Set up a f_ctx in the bio's bi_private and set the
512 	 * bi_end_io appropriately to trigger decryption when the bio is ended.
513 	 */
514 	f_ctx = mempool_alloc(bio_fallback_crypt_ctx_pool, GFP_NOIO);
515 	f_ctx->crypt_ctx = *bc;
516 	f_ctx->crypt_iter = bio->bi_iter;
517 	f_ctx->bi_private_orig = bio->bi_private;
518 	f_ctx->bi_end_io_orig = bio->bi_end_io;
519 	bio->bi_private = (void *)f_ctx;
520 	bio->bi_end_io = blk_crypto_fallback_decrypt_endio;
521 	bio_crypt_free_ctx(bio);
522 
523 	return true;
524 }
525 
526 int blk_crypto_fallback_evict_key(const struct blk_crypto_key *key)
527 {
528 	return __blk_crypto_evict_key(&blk_crypto_fallback_profile, key);
529 }
530 
531 static bool blk_crypto_fallback_inited;
532 static int blk_crypto_fallback_init(void)
533 {
534 	int i;
535 	int err;
536 	struct blk_crypto_profile *profile = &blk_crypto_fallback_profile;
537 
538 	if (blk_crypto_fallback_inited)
539 		return 0;
540 
541 	prandom_bytes(blank_key, BLK_CRYPTO_MAX_KEY_SIZE);
542 
543 	err = bioset_init(&crypto_bio_split, 64, 0, 0);
544 	if (err)
545 		goto out;
546 
547 	err = blk_crypto_profile_init(profile, blk_crypto_num_keyslots);
548 	if (err)
549 		goto fail_free_bioset;
550 	err = -ENOMEM;
551 
552 	profile->ll_ops = blk_crypto_fallback_ll_ops;
553 	profile->max_dun_bytes_supported = BLK_CRYPTO_MAX_IV_SIZE;
554 
555 	/* All blk-crypto modes have a crypto API fallback. */
556 	for (i = 0; i < BLK_ENCRYPTION_MODE_MAX; i++)
557 		profile->modes_supported[i] = 0xFFFFFFFF;
558 	profile->modes_supported[BLK_ENCRYPTION_MODE_INVALID] = 0;
559 
560 	blk_crypto_wq = alloc_workqueue("blk_crypto_wq",
561 					WQ_UNBOUND | WQ_HIGHPRI |
562 					WQ_MEM_RECLAIM, num_online_cpus());
563 	if (!blk_crypto_wq)
564 		goto fail_destroy_profile;
565 
566 	blk_crypto_keyslots = kcalloc(blk_crypto_num_keyslots,
567 				      sizeof(blk_crypto_keyslots[0]),
568 				      GFP_KERNEL);
569 	if (!blk_crypto_keyslots)
570 		goto fail_free_wq;
571 
572 	blk_crypto_bounce_page_pool =
573 		mempool_create_page_pool(num_prealloc_bounce_pg, 0);
574 	if (!blk_crypto_bounce_page_pool)
575 		goto fail_free_keyslots;
576 
577 	bio_fallback_crypt_ctx_cache = KMEM_CACHE(bio_fallback_crypt_ctx, 0);
578 	if (!bio_fallback_crypt_ctx_cache)
579 		goto fail_free_bounce_page_pool;
580 
581 	bio_fallback_crypt_ctx_pool =
582 		mempool_create_slab_pool(num_prealloc_fallback_crypt_ctxs,
583 					 bio_fallback_crypt_ctx_cache);
584 	if (!bio_fallback_crypt_ctx_pool)
585 		goto fail_free_crypt_ctx_cache;
586 
587 	blk_crypto_fallback_inited = true;
588 
589 	return 0;
590 fail_free_crypt_ctx_cache:
591 	kmem_cache_destroy(bio_fallback_crypt_ctx_cache);
592 fail_free_bounce_page_pool:
593 	mempool_destroy(blk_crypto_bounce_page_pool);
594 fail_free_keyslots:
595 	kfree(blk_crypto_keyslots);
596 fail_free_wq:
597 	destroy_workqueue(blk_crypto_wq);
598 fail_destroy_profile:
599 	blk_crypto_profile_destroy(profile);
600 fail_free_bioset:
601 	bioset_exit(&crypto_bio_split);
602 out:
603 	return err;
604 }
605 
606 /*
607  * Prepare blk-crypto-fallback for the specified crypto mode.
608  * Returns -ENOPKG if the needed crypto API support is missing.
609  */
610 int blk_crypto_fallback_start_using_mode(enum blk_crypto_mode_num mode_num)
611 {
612 	const char *cipher_str = blk_crypto_modes[mode_num].cipher_str;
613 	struct blk_crypto_fallback_keyslot *slotp;
614 	unsigned int i;
615 	int err = 0;
616 
617 	/*
618 	 * Fast path
619 	 * Ensure that updates to blk_crypto_keyslots[i].tfms[mode_num]
620 	 * for each i are visible before we try to access them.
621 	 */
622 	if (likely(smp_load_acquire(&tfms_inited[mode_num])))
623 		return 0;
624 
625 	mutex_lock(&tfms_init_lock);
626 	if (tfms_inited[mode_num])
627 		goto out;
628 
629 	err = blk_crypto_fallback_init();
630 	if (err)
631 		goto out;
632 
633 	for (i = 0; i < blk_crypto_num_keyslots; i++) {
634 		slotp = &blk_crypto_keyslots[i];
635 		slotp->tfms[mode_num] = crypto_alloc_skcipher(cipher_str, 0, 0);
636 		if (IS_ERR(slotp->tfms[mode_num])) {
637 			err = PTR_ERR(slotp->tfms[mode_num]);
638 			if (err == -ENOENT) {
639 				pr_warn_once("Missing crypto API support for \"%s\"\n",
640 					     cipher_str);
641 				err = -ENOPKG;
642 			}
643 			slotp->tfms[mode_num] = NULL;
644 			goto out_free_tfms;
645 		}
646 
647 		crypto_skcipher_set_flags(slotp->tfms[mode_num],
648 					  CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
649 	}
650 
651 	/*
652 	 * Ensure that updates to blk_crypto_keyslots[i].tfms[mode_num]
653 	 * for each i are visible before we set tfms_inited[mode_num].
654 	 */
655 	smp_store_release(&tfms_inited[mode_num], true);
656 	goto out;
657 
658 out_free_tfms:
659 	for (i = 0; i < blk_crypto_num_keyslots; i++) {
660 		slotp = &blk_crypto_keyslots[i];
661 		crypto_free_skcipher(slotp->tfms[mode_num]);
662 		slotp->tfms[mode_num] = NULL;
663 	}
664 out:
665 	mutex_unlock(&tfms_init_lock);
666 	return err;
667 }
668