// SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright 2019 Google LLC
   */
  
  /*
   * Refer to Documentation/block/inline-encryption.rst for detailed explanation.
   */
  
  #define pr_fmt(fmt) "blk-crypto-fallback: " fmt
  
  #include <crypto/skcipher.h>
  #include <linux/blk-cgroup.h>
  #include <linux/blk-crypto.h>

  #include <linux/blkdev.h>

  #include <linux/crypto.h>
  #include <linux/keyslot-manager.h>
  #include <linux/mempool.h>
  #include <linux/module.h>
  #include <linux/random.h>
  
  #include "blk-crypto-internal.h"
  
  static unsigned int num_prealloc_bounce_pg = 32;
  module_param(num_prealloc_bounce_pg, uint, 0);
  MODULE_PARM_DESC(num_prealloc_bounce_pg,
  		 "Number of preallocated bounce pages for the blk-crypto crypto API fallback");
  
  static unsigned int blk_crypto_num_keyslots = 100;
  module_param_named(num_keyslots, blk_crypto_num_keyslots, uint, 0);
  MODULE_PARM_DESC(num_keyslots,
  		 "Number of keyslots for the blk-crypto crypto API fallback");
  
  static unsigned int num_prealloc_fallback_crypt_ctxs = 128;
  module_param(num_prealloc_fallback_crypt_ctxs, uint, 0);
  MODULE_PARM_DESC(num_prealloc_crypt_fallback_ctxs,
  		 "Number of preallocated bio fallback crypto contexts for blk-crypto to use during crypto API fallback");
  
  struct bio_fallback_crypt_ctx {
  	struct bio_crypt_ctx crypt_ctx;
  	/*
  	 * Copy of the bvec_iter when this bio was submitted.
  	 * We only want to en/decrypt the part of the bio as described by the
  	 * bvec_iter upon submission because bio might be split before being
  	 * resubmitted
  	 */
  	struct bvec_iter crypt_iter;

  	union {
  		struct {
  			struct work_struct work;
  			struct bio *bio;
  		};
  		struct {
  			void *bi_private_orig;
  			bio_end_io_t *bi_end_io_orig;
  		};
  	};

  };

  static struct kmem_cache *bio_fallback_crypt_ctx_cache;
  static mempool_t *bio_fallback_crypt_ctx_pool;
  
  /*
   * Allocating a crypto tfm during I/O can deadlock, so we have to preallocate
   * all of a mode's tfms when that mode starts being used. Since each mode may
   * need all the keyslots at some point, each mode needs its own tfm for each
   * keyslot; thus, a keyslot may contain tfms for multiple modes.  However, to
   * match the behavior of real inline encryption hardware (which only supports a
   * single encryption context per keyslot), we only allow one tfm per keyslot to
   * be used at a time - the rest of the unused tfms have their keys cleared.
   */
  static DEFINE_MUTEX(tfms_init_lock);
  static bool tfms_inited[BLK_ENCRYPTION_MODE_MAX];

  static struct blk_crypto_keyslot {

  	enum blk_crypto_mode_num crypto_mode;
  	struct crypto_skcipher *tfms[BLK_ENCRYPTION_MODE_MAX];
  } *blk_crypto_keyslots;

  static struct blk_keyslot_manager blk_crypto_ksm;

  static struct workqueue_struct *blk_crypto_wq;
  static mempool_t *blk_crypto_bounce_page_pool;

  
  /*
   * This is the key we set when evicting a keyslot. This *should* be the all 0's
   * key, but AES-XTS rejects that key, so we use some random bytes instead.
   */
  static u8 blank_key[BLK_CRYPTO_MAX_KEY_SIZE];
  
  static void blk_crypto_evict_keyslot(unsigned int slot)
  {
  	struct blk_crypto_keyslot *slotp = &blk_crypto_keyslots[slot];
  	enum blk_crypto_mode_num crypto_mode = slotp->crypto_mode;
  	int err;
  
  	WARN_ON(slotp->crypto_mode == BLK_ENCRYPTION_MODE_INVALID);
  
  	/* Clear the key in the skcipher */
  	err = crypto_skcipher_setkey(slotp->tfms[crypto_mode], blank_key,
  				     blk_crypto_modes[crypto_mode].keysize);
  	WARN_ON(err);
  	slotp->crypto_mode = BLK_ENCRYPTION_MODE_INVALID;
  }

  static int blk_crypto_keyslot_program(struct blk_keyslot_manager *ksm,

  				      const struct blk_crypto_key *key,
  				      unsigned int slot)
  {
  	struct blk_crypto_keyslot *slotp = &blk_crypto_keyslots[slot];

  	const enum blk_crypto_mode_num crypto_mode =
  						key->crypto_cfg.crypto_mode;

  	int err;
  
  	if (crypto_mode != slotp->crypto_mode &&

  	    slotp->crypto_mode != BLK_ENCRYPTION_MODE_INVALID)

  		blk_crypto_evict_keyslot(slot);

  	slotp->crypto_mode = crypto_mode;
  	err = crypto_skcipher_setkey(slotp->tfms[crypto_mode], key->raw,
  				     key->size);
  	if (err) {
  		blk_crypto_evict_keyslot(slot);
  		return err;
  	}
  	return 0;
  }

  static int blk_crypto_keyslot_evict(struct blk_keyslot_manager *ksm,

  				    const struct blk_crypto_key *key,
  				    unsigned int slot)
  {
  	blk_crypto_evict_keyslot(slot);
  	return 0;
  }
  
  /*
   * The crypto API fallback KSM ops - only used for a bio when it specifies a

   * blk_crypto_key that was not supported by the device's inline encryption
   * hardware.

   */

  static const struct blk_ksm_ll_ops blk_crypto_ksm_ll_ops = {

  	.keyslot_program	= blk_crypto_keyslot_program,
  	.keyslot_evict		= blk_crypto_keyslot_evict,
  };

  static void blk_crypto_fallback_encrypt_endio(struct bio *enc_bio)

  {
  	struct bio *src_bio = enc_bio->bi_private;
  	int i;
  
  	for (i = 0; i < enc_bio->bi_vcnt; i++)
  		mempool_free(enc_bio->bi_io_vec[i].bv_page,
  			     blk_crypto_bounce_page_pool);
  
  	src_bio->bi_status = enc_bio->bi_status;
  
  	bio_put(enc_bio);
  	bio_endio(src_bio);
  }
  
  static struct bio *blk_crypto_clone_bio(struct bio *bio_src)
  {
  	struct bvec_iter iter;
  	struct bio_vec bv;
  	struct bio *bio;
  
  	bio = bio_alloc_bioset(GFP_NOIO, bio_segments(bio_src), NULL);
  	if (!bio)
  		return NULL;
  	bio->bi_disk		= bio_src->bi_disk;
  	bio->bi_opf		= bio_src->bi_opf;
  	bio->bi_ioprio		= bio_src->bi_ioprio;
  	bio->bi_write_hint	= bio_src->bi_write_hint;
  	bio->bi_iter.bi_sector	= bio_src->bi_iter.bi_sector;
  	bio->bi_iter.bi_size	= bio_src->bi_iter.bi_size;
  
  	bio_for_each_segment(bv, bio_src, iter)
  		bio->bi_io_vec[bio->bi_vcnt++] = bv;

  	bio_clone_blkg_association(bio, bio_src);
  	blkcg_bio_issue_init(bio);

  	bio_clone_skip_dm_default_key(bio, bio_src);

  	return bio;
  }

  static bool blk_crypto_alloc_cipher_req(struct blk_ksm_keyslot *slot,
  					struct skcipher_request **ciph_req_ret,
  					struct crypto_wait *wait)

  {
  	struct skcipher_request *ciph_req;
  	const struct blk_crypto_keyslot *slotp;

  	int keyslot_idx = blk_ksm_get_slot_idx(slot);

  	slotp = &blk_crypto_keyslots[keyslot_idx];

  	ciph_req = skcipher_request_alloc(slotp->tfms[slotp->crypto_mode],
  					  GFP_NOIO);

  	if (!ciph_req)
  		return false;

  
  	skcipher_request_set_callback(ciph_req,
  				      CRYPTO_TFM_REQ_MAY_BACKLOG |
  				      CRYPTO_TFM_REQ_MAY_SLEEP,
  				      crypto_req_done, wait);
  	*ciph_req_ret = ciph_req;

  
  	return true;

  }

  static bool blk_crypto_split_bio_if_needed(struct bio **bio_ptr)

  {
  	struct bio *bio = *bio_ptr;
  	unsigned int i = 0;
  	unsigned int num_sectors = 0;
  	struct bio_vec bv;
  	struct bvec_iter iter;
  
  	bio_for_each_segment(bv, bio, iter) {
  		num_sectors += bv.bv_len >> SECTOR_SHIFT;
  		if (++i == BIO_MAX_PAGES)
  			break;
  	}
  	if (num_sectors < bio_sectors(bio)) {
  		struct bio *split_bio;
  
  		split_bio = bio_split(bio, num_sectors, GFP_NOIO, NULL);
  		if (!split_bio) {
  			bio->bi_status = BLK_STS_RESOURCE;

  			return false;

  		}
  		bio_chain(split_bio, bio);

  		submit_bio_noacct(bio);

  		*bio_ptr = split_bio;
  	}

  
  	return true;

  }
  
  union blk_crypto_iv {
  	__le64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
  	u8 bytes[BLK_CRYPTO_MAX_IV_SIZE];
  };
  
  static void blk_crypto_dun_to_iv(const u64 dun[BLK_CRYPTO_DUN_ARRAY_SIZE],
  				 union blk_crypto_iv *iv)
  {
  	int i;
  
  	for (i = 0; i < BLK_CRYPTO_DUN_ARRAY_SIZE; i++)
  		iv->dun[i] = cpu_to_le64(dun[i]);
  }
  
  /*
   * The crypto API fallback's encryption routine.
   * Allocate a bounce bio for encryption, encrypt the input bio using crypto API,
   * and replace *bio_ptr with the bounce bio. May split input bio if it's too

   * large. Returns true on success. Returns false and sets bio->bi_status on
   * error.

   */

  static bool blk_crypto_fallback_encrypt_bio(struct bio **bio_ptr)

  {

  	struct bio *src_bio, *enc_bio;
  	struct bio_crypt_ctx *bc;
  	struct blk_ksm_keyslot *slot;
  	int data_unit_size;

  	struct skcipher_request *ciph_req = NULL;
  	DECLARE_CRYPTO_WAIT(wait);
  	u64 curr_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];

  	struct scatterlist src, dst;

  	union blk_crypto_iv iv;

  	unsigned int i, j;

  	bool ret = false;
  	blk_status_t blk_st;

  
  	/* Split the bio if it's too big for single page bvec */

  	if (!blk_crypto_split_bio_if_needed(bio_ptr))
  		return false;

  
  	src_bio = *bio_ptr;
  	bc = src_bio->bi_crypt_context;

  	data_unit_size = bc->bc_key->crypto_cfg.data_unit_size;

  
  	/* Allocate bounce bio for encryption */
  	enc_bio = blk_crypto_clone_bio(src_bio);
  	if (!enc_bio) {
  		src_bio->bi_status = BLK_STS_RESOURCE;

  		return false;

  	}
  
  	/*
  	 * Use the crypto API fallback keyslot manager to get a crypto_skcipher
  	 * for the algorithm and key specified for this bio.
  	 */

  	blk_st = blk_ksm_get_slot_for_key(&blk_crypto_ksm, bc->bc_key, &slot);
  	if (blk_st != BLK_STS_OK) {
  		src_bio->bi_status = blk_st;

  		goto out_put_enc_bio;
  	}
  
  	/* and then allocate an skcipher_request for it */

  	if (!blk_crypto_alloc_cipher_req(slot, &ciph_req, &wait)) {
  		src_bio->bi_status = BLK_STS_RESOURCE;

  		goto out_release_keyslot;

  	}

  
  	memcpy(curr_dun, bc->bc_dun, sizeof(curr_dun));
  	sg_init_table(&src, 1);
  	sg_init_table(&dst, 1);
  
  	skcipher_request_set_crypt(ciph_req, &src, &dst, data_unit_size,
  				   iv.bytes);
  
  	/* Encrypt each page in the bounce bio */
  	for (i = 0; i < enc_bio->bi_vcnt; i++) {
  		struct bio_vec *enc_bvec = &enc_bio->bi_io_vec[i];
  		struct page *plaintext_page = enc_bvec->bv_page;
  		struct page *ciphertext_page =
  			mempool_alloc(blk_crypto_bounce_page_pool, GFP_NOIO);
  
  		enc_bvec->bv_page = ciphertext_page;
  
  		if (!ciphertext_page) {
  			src_bio->bi_status = BLK_STS_RESOURCE;

  			goto out_free_bounce_pages;
  		}
  
  		sg_set_page(&src, plaintext_page, data_unit_size,
  			    enc_bvec->bv_offset);
  		sg_set_page(&dst, ciphertext_page, data_unit_size,
  			    enc_bvec->bv_offset);
  
  		/* Encrypt each data unit in this page */
  		for (j = 0; j < enc_bvec->bv_len; j += data_unit_size) {
  			blk_crypto_dun_to_iv(curr_dun, &iv);

  			if (crypto_wait_req(crypto_skcipher_encrypt(ciph_req),
  					    &wait)) {

  				i++;

  				src_bio->bi_status = BLK_STS_IOERR;

  				goto out_free_bounce_pages;
  			}
  			bio_crypt_dun_increment(curr_dun, 1);
  			src.offset += data_unit_size;
  			dst.offset += data_unit_size;
  		}
  	}
  
  	enc_bio->bi_private = src_bio;

  	enc_bio->bi_end_io = blk_crypto_fallback_encrypt_endio;

  	*bio_ptr = enc_bio;

  	ret = true;

  
  	enc_bio = NULL;

  	goto out_free_ciph_req;
  
  out_free_bounce_pages:
  	while (i > 0)
  		mempool_free(enc_bio->bi_io_vec[--i].bv_page,
  			     blk_crypto_bounce_page_pool);
  out_free_ciph_req:
  	skcipher_request_free(ciph_req);
  out_release_keyslot:

  	blk_ksm_put_slot(slot);

  out_put_enc_bio:
  	if (enc_bio)
  		bio_put(enc_bio);

  	return ret;

  }
  
  /*
   * The crypto API fallback's main decryption routine.

   * Decrypts input bio in place, and calls bio_endio on the bio.

   */

  static void blk_crypto_fallback_decrypt_bio(struct work_struct *work)

  {

  	struct bio_fallback_crypt_ctx *f_ctx =
  		container_of(work, struct bio_fallback_crypt_ctx, work);
  	struct bio *bio = f_ctx->bio;
  	struct bio_crypt_ctx *bc = &f_ctx->crypt_ctx;
  	struct blk_ksm_keyslot *slot;

  	struct skcipher_request *ciph_req = NULL;
  	DECLARE_CRYPTO_WAIT(wait);

  	u64 curr_dun[BLK_CRYPTO_DUN_ARRAY_SIZE];
  	union blk_crypto_iv iv;
  	struct scatterlist sg;

  	struct bio_vec bv;
  	struct bvec_iter iter;
  	const int data_unit_size = bc->bc_key->crypto_cfg.data_unit_size;

  	unsigned int i;

  	blk_status_t blk_st;

  
  	/*
  	 * Use the crypto API fallback keyslot manager to get a crypto_skcipher
  	 * for the algorithm and key specified for this bio.
  	 */

  	blk_st = blk_ksm_get_slot_for_key(&blk_crypto_ksm, bc->bc_key, &slot);
  	if (blk_st != BLK_STS_OK) {
  		bio->bi_status = blk_st;

  		goto out_no_keyslot;
  	}
  
  	/* and then allocate an skcipher_request for it */

  	if (!blk_crypto_alloc_cipher_req(slot, &ciph_req, &wait)) {
  		bio->bi_status = BLK_STS_RESOURCE;

  		goto out;

  	}

  	memcpy(curr_dun, bc->bc_dun, sizeof(curr_dun));

  	sg_init_table(&sg, 1);
  	skcipher_request_set_crypt(ciph_req, &sg, &sg, data_unit_size,
  				   iv.bytes);
  
  	/* Decrypt each segment in the bio */
  	__bio_for_each_segment(bv, bio, iter, f_ctx->crypt_iter) {
  		struct page *page = bv.bv_page;
  
  		sg_set_page(&sg, page, data_unit_size, bv.bv_offset);
  
  		/* Decrypt each data unit in the segment */
  		for (i = 0; i < bv.bv_len; i += data_unit_size) {
  			blk_crypto_dun_to_iv(curr_dun, &iv);
  			if (crypto_wait_req(crypto_skcipher_decrypt(ciph_req),
  					    &wait)) {
  				bio->bi_status = BLK_STS_IOERR;
  				goto out;
  			}
  			bio_crypt_dun_increment(curr_dun, 1);
  			sg.offset += data_unit_size;
  		}
  	}
  
  out:
  	skcipher_request_free(ciph_req);

  	blk_ksm_put_slot(slot);

  out_no_keyslot:

  	mempool_free(f_ctx, bio_fallback_crypt_ctx_pool);

  	bio_endio(bio);
  }

  /**
   * blk_crypto_fallback_decrypt_endio - queue bio for fallback decryption
   *
   * @bio: the bio to queue
   *
   * Restore bi_private and bi_end_io, and queue the bio for decryption into a
   * workqueue, since this function will be called from an atomic context.

   */

  static void blk_crypto_fallback_decrypt_endio(struct bio *bio)

  {

  	struct bio_fallback_crypt_ctx *f_ctx = bio->bi_private;
  
  	bio->bi_private = f_ctx->bi_private_orig;
  	bio->bi_end_io = f_ctx->bi_end_io_orig;

  
  	/* If there was an IO error, don't queue for decrypt. */

  	if (bio->bi_status) {
  		mempool_free(f_ctx, bio_fallback_crypt_ctx_pool);
  		bio_endio(bio);
  		return;
  	}

  	INIT_WORK(&f_ctx->work, blk_crypto_fallback_decrypt_bio);
  	f_ctx->bio = bio;
  	queue_work(blk_crypto_wq, &f_ctx->work);
  }
  
  /**
   * blk_crypto_fallback_bio_prep - Prepare a bio to use fallback en/decryption
   *
   * @bio_ptr: pointer to the bio to prepare
   *
   * If bio is doing a WRITE operation, this splits the bio into two parts if it's
   * too big (see blk_crypto_split_bio_if_needed). It then allocates a bounce bio
   * for the first part, encrypts it, and update bio_ptr to point to the bounce
   * bio.
   *
   * For a READ operation, we mark the bio for decryption by using bi_private and
   * bi_end_io.
   *
   * In either case, this function will make the bio look like a regular bio (i.e.
   * as if no encryption context was ever specified) for the purposes of the rest
   * of the stack except for blk-integrity (blk-integrity and blk-crypto are not
   * currently supported together).
   *
   * Return: true on success. Sets bio->bi_status and returns false on error.
   */
  bool blk_crypto_fallback_bio_prep(struct bio **bio_ptr)
  {
  	struct bio *bio = *bio_ptr;
  	struct bio_crypt_ctx *bc = bio->bi_crypt_context;
  	struct bio_fallback_crypt_ctx *f_ctx;

  	if (WARN_ON_ONCE(!tfms_inited[bc->bc_key->crypto_cfg.crypto_mode])) {
  		/* User didn't call blk_crypto_start_using_key() first */
  		bio->bi_status = BLK_STS_IOERR;
  		return false;
  	}
  
  	if (!blk_ksm_crypto_cfg_supported(&blk_crypto_ksm,
  					  &bc->bc_key->crypto_cfg)) {
  		bio->bi_status = BLK_STS_NOTSUPP;
  		return false;

  	}

  	if (bio_data_dir(bio) == WRITE)
  		return blk_crypto_fallback_encrypt_bio(bio_ptr);
  
  	/*
  	 * bio READ case: Set up a f_ctx in the bio's bi_private and set the
  	 * bi_end_io appropriately to trigger decryption when the bio is ended.
  	 */
  	f_ctx = mempool_alloc(bio_fallback_crypt_ctx_pool, GFP_NOIO);
  	f_ctx->crypt_ctx = *bc;
  	f_ctx->crypt_iter = bio->bi_iter;
  	f_ctx->bi_private_orig = bio->bi_private;
  	f_ctx->bi_end_io_orig = bio->bi_end_io;
  	bio->bi_private = (void *)f_ctx;
  	bio->bi_end_io = blk_crypto_fallback_decrypt_endio;
  	bio_crypt_free_ctx(bio);

  
  	return true;

  }
  
  int blk_crypto_fallback_evict_key(const struct blk_crypto_key *key)
  {
  	return blk_ksm_evict_key(&blk_crypto_ksm, key);
  }
  
  static bool blk_crypto_fallback_inited;
  static int blk_crypto_fallback_init(void)
  {
  	int i;

  	int err;

  
  	if (blk_crypto_fallback_inited)
  		return 0;
  
  	prandom_bytes(blank_key, BLK_CRYPTO_MAX_KEY_SIZE);
  
  	err = blk_ksm_init(&blk_crypto_ksm, blk_crypto_num_keyslots);
  	if (err)
  		goto out;
  	err = -ENOMEM;
  
  	blk_crypto_ksm.ksm_ll_ops = blk_crypto_ksm_ll_ops;
  	blk_crypto_ksm.max_dun_bytes_supported = BLK_CRYPTO_MAX_IV_SIZE;
  	blk_crypto_ksm.features = BLK_CRYPTO_FEATURE_STANDARD_KEYS;
  
  	/* All blk-crypto modes have a crypto API fallback. */
  	for (i = 0; i < BLK_ENCRYPTION_MODE_MAX; i++)
  		blk_crypto_ksm.crypto_modes_supported[i] = 0xFFFFFFFF;
  	blk_crypto_ksm.crypto_modes_supported[BLK_ENCRYPTION_MODE_INVALID] = 0;
  
  	blk_crypto_wq = alloc_workqueue("blk_crypto_wq",
  					WQ_UNBOUND | WQ_HIGHPRI |
  					WQ_MEM_RECLAIM, num_online_cpus());
  	if (!blk_crypto_wq)
  		goto fail_free_ksm;
  
  	blk_crypto_keyslots = kcalloc(blk_crypto_num_keyslots,
  				      sizeof(blk_crypto_keyslots[0]),
  				      GFP_KERNEL);
  	if (!blk_crypto_keyslots)
  		goto fail_free_wq;
  
  	blk_crypto_bounce_page_pool =
  		mempool_create_page_pool(num_prealloc_bounce_pg, 0);
  	if (!blk_crypto_bounce_page_pool)
  		goto fail_free_keyslots;
  
  	bio_fallback_crypt_ctx_cache = KMEM_CACHE(bio_fallback_crypt_ctx, 0);
  	if (!bio_fallback_crypt_ctx_cache)
  		goto fail_free_bounce_page_pool;
  
  	bio_fallback_crypt_ctx_pool =
  		mempool_create_slab_pool(num_prealloc_fallback_crypt_ctxs,
  					 bio_fallback_crypt_ctx_cache);
  	if (!bio_fallback_crypt_ctx_pool)
  		goto fail_free_crypt_ctx_cache;
  
  	blk_crypto_fallback_inited = true;
  
  	return 0;
  fail_free_crypt_ctx_cache:
  	kmem_cache_destroy(bio_fallback_crypt_ctx_cache);
  fail_free_bounce_page_pool:
  	mempool_destroy(blk_crypto_bounce_page_pool);
  fail_free_keyslots:
  	kfree(blk_crypto_keyslots);
  fail_free_wq:
  	destroy_workqueue(blk_crypto_wq);
  fail_free_ksm:
  	blk_ksm_destroy(&blk_crypto_ksm);

  out:

  	return err;

  }

  /*
   * Prepare blk-crypto-fallback for the specified crypto mode.
   * Returns -ENOPKG if the needed crypto API support is missing.

   */

  int blk_crypto_fallback_start_using_mode(enum blk_crypto_mode_num mode_num)

  {

  	const char *cipher_str = blk_crypto_modes[mode_num].cipher_str;

  	struct blk_crypto_keyslot *slotp;
  	unsigned int i;
  	int err = 0;
  
  	/*
  	 * Fast path
  	 * Ensure that updates to blk_crypto_keyslots[i].tfms[mode_num]
  	 * for each i are visible before we try to access them.
  	 */
  	if (likely(smp_load_acquire(&tfms_inited[mode_num])))
  		return 0;

  	mutex_lock(&tfms_init_lock);

  	if (tfms_inited[mode_num])
  		goto out;
  
  	err = blk_crypto_fallback_init();
  	if (err)

  		goto out;
  
  	for (i = 0; i < blk_crypto_num_keyslots; i++) {
  		slotp = &blk_crypto_keyslots[i];

  		slotp->tfms[mode_num] = crypto_alloc_skcipher(cipher_str, 0, 0);

  		if (IS_ERR(slotp->tfms[mode_num])) {
  			err = PTR_ERR(slotp->tfms[mode_num]);

  			if (err == -ENOENT) {
  				pr_warn_once("Missing crypto API support for \"%s\"
  ",
  					     cipher_str);
  				err = -ENOPKG;
  			}

  			slotp->tfms[mode_num] = NULL;
  			goto out_free_tfms;
  		}
  
  		crypto_skcipher_set_flags(slotp->tfms[mode_num],
  					  CRYPTO_TFM_REQ_FORBID_WEAK_KEYS);
  	}
  
  	/*
  	 * Ensure that updates to blk_crypto_keyslots[i].tfms[mode_num]
  	 * for each i are visible before we set tfms_inited[mode_num].
  	 */
  	smp_store_release(&tfms_inited[mode_num], true);
  	goto out;
  
  out_free_tfms:
  	for (i = 0; i < blk_crypto_num_keyslots; i++) {
  		slotp = &blk_crypto_keyslots[i];
  		crypto_free_skcipher(slotp->tfms[mode_num]);
  		slotp->tfms[mode_num] = NULL;
  	}
  out:
  	mutex_unlock(&tfms_init_lock);
  	return err;
  }