Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 678 insertions, 0 deletions

diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c
new file mode 100644
index 0000000000..e6468eab26
--- /dev/null
+++ b/block/blk-crypto-fallback.c
@@ -0,0 +1,678 @@
+// 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-crypto.h>
+#include <linux/blk-crypto-profile.h>
+#include <linux/blkdev.h>
+#include <linux/crypto.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/random.h>
+#include <linux/scatterlist.h>
+
+#include "blk-cgroup.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_fallback_keyslot {
+	enum blk_crypto_mode_num crypto_mode;
+	struct crypto_skcipher *tfms[BLK_ENCRYPTION_MODE_MAX];
+} *blk_crypto_keyslots;
+
+static struct blk_crypto_profile *blk_crypto_fallback_profile;
+static struct workqueue_struct *blk_crypto_wq;
+static mempool_t *blk_crypto_bounce_page_pool;
+static struct bio_set crypto_bio_split;
+
+/*
+ * 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_fallback_evict_keyslot(unsigned int slot)
+{
+	struct blk_crypto_fallback_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_fallback_keyslot_program(struct blk_crypto_profile *profile,
+				    const struct blk_crypto_key *key,
+				    unsigned int slot)
+{
+	struct blk_crypto_fallback_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_fallback_evict_keyslot(slot);
+
+	slotp->crypto_mode = crypto_mode;
+	err = crypto_skcipher_setkey(slotp->tfms[crypto_mode], key->raw,
+				     key->size);
+	if (err) {
+		blk_crypto_fallback_evict_keyslot(slot);
+		return err;
+	}
+	return 0;
+}
+
+static int blk_crypto_fallback_keyslot_evict(struct blk_crypto_profile *profile,
+					     const struct blk_crypto_key *key,
+					     unsigned int slot)
+{
+	blk_crypto_fallback_evict_keyslot(slot);
+	return 0;
+}
+
+static const struct blk_crypto_ll_ops blk_crypto_fallback_ll_ops = {
+	.keyslot_program        = blk_crypto_fallback_keyslot_program,
+	.keyslot_evict          = blk_crypto_fallback_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_uninit(enc_bio);
+	kfree(enc_bio);
+	bio_endio(src_bio);
+}
+
+static struct bio *blk_crypto_fallback_clone_bio(struct bio *bio_src)
+{
+	unsigned int nr_segs = bio_segments(bio_src);
+	struct bvec_iter iter;
+	struct bio_vec bv;
+	struct bio *bio;
+
+	bio = bio_kmalloc(nr_segs, GFP_NOIO);
+	if (!bio)
+		return NULL;
+	bio_init(bio, bio_src->bi_bdev, bio->bi_inline_vecs, nr_segs,
+		 bio_src->bi_opf);
+	if (bio_flagged(bio_src, BIO_REMAPPED))
+		bio_set_flag(bio, BIO_REMAPPED);
+	bio->bi_ioprio		= bio_src->bi_ioprio;
+	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);
+
+	return bio;
+}
+
+static bool
+blk_crypto_fallback_alloc_cipher_req(struct blk_crypto_keyslot *slot,
+				     struct skcipher_request **ciph_req_ret,
+				     struct crypto_wait *wait)
+{
+	struct skcipher_request *ciph_req;
+	const struct blk_crypto_fallback_keyslot *slotp;
+	int keyslot_idx = blk_crypto_keyslot_index(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_fallback_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_VECS)
+			break;
+	}
+	if (num_sectors < bio_sectors(bio)) {
+		struct bio *split_bio;
+
+		split_bio = bio_split(bio, num_sectors, GFP_NOIO,
+				      &crypto_bio_split);
+		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_crypto_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_fallback_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_fallback_clone_bio(src_bio);
+	if (!enc_bio) {
+		src_bio->bi_status = BLK_STS_RESOURCE;
+		return false;
+	}
+
+	/*
+	 * Get a blk-crypto-fallback keyslot that contains a crypto_skcipher for
+	 * this bio's algorithm and key.
+	 */
+	blk_st = blk_crypto_get_keyslot(blk_crypto_fallback_profile,
+					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_fallback_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_crypto_put_keyslot(slot);
+out_put_enc_bio:
+	if (enc_bio)
+		bio_uninit(enc_bio);
+	kfree(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_crypto_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;
+
+	/*
+	 * Get a blk-crypto-fallback keyslot that contains a crypto_skcipher for
+	 * this bio's algorithm and key.
+	 */
+	blk_st = blk_crypto_get_keyslot(blk_crypto_fallback_profile,
+					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_fallback_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_crypto_put_keyslot(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_fallback_split_bio_if_needed()). It then allocates a
+ * bounce bio for the first part, encrypts it, and updates 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_crypto_cfg_supported(blk_crypto_fallback_profile,
+					&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_crypto_evict_key(blk_crypto_fallback_profile, 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;
+
+	get_random_bytes(blank_key, BLK_CRYPTO_MAX_KEY_SIZE);
+
+	err = bioset_init(&crypto_bio_split, 64, 0, 0);
+	if (err)
+		goto out;
+
+	/* Dynamic allocation is needed because of lockdep_register_key(). */
+	blk_crypto_fallback_profile =
+		kzalloc(sizeof(*blk_crypto_fallback_profile), GFP_KERNEL);
+	if (!blk_crypto_fallback_profile) {
+		err = -ENOMEM;
+		goto fail_free_bioset;
+	}
+
+	err = blk_crypto_profile_init(blk_crypto_fallback_profile,
+				      blk_crypto_num_keyslots);
+	if (err)
+		goto fail_free_profile;
+	err = -ENOMEM;
+
+	blk_crypto_fallback_profile->ll_ops = blk_crypto_fallback_ll_ops;
+	blk_crypto_fallback_profile->max_dun_bytes_supported = BLK_CRYPTO_MAX_IV_SIZE;
+
+	/* All blk-crypto modes have a crypto API fallback. */
+	for (i = 0; i < BLK_ENCRYPTION_MODE_MAX; i++)
+		blk_crypto_fallback_profile->modes_supported[i] = 0xFFFFFFFF;
+	blk_crypto_fallback_profile->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_destroy_profile;
+
+	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_destroy_profile:
+	blk_crypto_profile_destroy(blk_crypto_fallback_profile);
+fail_free_profile:
+	kfree(blk_crypto_fallback_profile);
+fail_free_bioset:
+	bioset_exit(&crypto_bio_split);
+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_fallback_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\"\n",
+					     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;
+}