text: // SPDX-License-Identifier: GPL-2.0-or-later
  /* XTS: as defined in IEEE1619/D16
   *	http://grouper.ieee.org/groups/1619/email/pdf00086.pdf
   *
   * Copyright (c) 2007 Rik Snel <rsnel@cube.dyndns.org>
   *
   * Based on ecb.c
   * Copyright (c) 2006 Herbert Xu <herbert@gondor.apana.org.au>
   */
  #include <crypto/internal/skcipher.h>
  #include <crypto/scatterwalk.h>
  #include <linux/err.h>
  #include <linux/init.h>
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/scatterlist.h>
  #include <linux/slab.h>
  
  #include <crypto/xts.h>
  #include <crypto/b128ops.h>
  #include <crypto/gf128mul.h>
  
  struct priv {
  	struct crypto_skcipher *child;
  	struct crypto_cipher *tweak;
  };
  
  struct xts_instance_ctx {
  	struct crypto_skcipher_spawn spawn;
  	char name[CRYPTO_MAX_ALG_NAME];
  };
  
  struct rctx {
  	le128 t;
  	struct scatterlist *tail;
  	struct scatterlist sg[2];
  	struct skcipher_request subreq;
  };
  
  static int setkey(struct crypto_skcipher *parent, const u8 *key,
  		  unsigned int keylen)
  {
  	struct priv *ctx = crypto_skcipher_ctx(parent);
  	struct crypto_skcipher *child;
  	struct crypto_cipher *tweak;
  	int err;
  
  	err = xts_verify_key(parent, key, keylen);
  	if (err)
  		return err;
  
  	keylen /= 2;
  
  	/* we need two cipher instances: one to compute the initial 'tweak'
  	 * by encrypting the IV (usually the 'plain' iv) and the other
  	 * one to encrypt and decrypt the data */
  
  	/* tweak cipher, uses Key2 i.e. the second half of *key */
  	tweak = ctx->tweak;
  	crypto_cipher_clear_flags(tweak, CRYPTO_TFM_REQ_MASK);
  	crypto_cipher_set_flags(tweak, crypto_skcipher_get_flags(parent) &
  				       CRYPTO_TFM_REQ_MASK);
  	err = crypto_cipher_setkey(tweak, key + keylen, keylen);
  	if (err)
  		return err;
  
  	/* data cipher, uses Key1 i.e. the first half of *key */
  	child = ctx->child;
  	crypto_skcipher_clear_flags(child, CRYPTO_TFM_REQ_MASK);
  	crypto_skcipher_set_flags(child, crypto_skcipher_get_flags(parent) &
  					 CRYPTO_TFM_REQ_MASK);
  	return crypto_skcipher_setkey(child, key, keylen);
  }
  
  /*
   * We compute the tweak masks twice (both before and after the ECB encryption or
   * decryption) to avoid having to allocate a temporary buffer and/or make
   * mutliple calls to the 'ecb(..)' instance, which usually would be slower than
   * just doing the gf128mul_x_ble() calls again.
   */
  static int xor_tweak(struct skcipher_request *req, bool second_pass, bool enc)
  {
  	struct rctx *rctx = skcipher_request_ctx(req);
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	const bool cts = (req->cryptlen % XTS_BLOCK_SIZE);
  	const int bs = XTS_BLOCK_SIZE;
  	struct skcipher_walk w;
  	le128 t = rctx->t;
  	int err;
  
  	if (second_pass) {
  		req = &rctx->subreq;
  		/* set to our TFM to enforce correct alignment: */
  		skcipher_request_set_tfm(req, tfm);
  	}
  	err = skcipher_walk_virt(&w, req, false);
  
  	while (w.nbytes) {
  		unsigned int avail = w.nbytes;
  		le128 *wsrc;
  		le128 *wdst;
  
  		wsrc = w.src.virt.addr;
  		wdst = w.dst.virt.addr;
  
  		do {
  			if (unlikely(cts) &&
  			    w.total - w.nbytes + avail < 2 * XTS_BLOCK_SIZE) {
  				if (!enc) {
  					if (second_pass)
  						rctx->t = t;
  					gf128mul_x_ble(&t, &t);
  				}
  				le128_xor(wdst, &t, wsrc);
  				if (enc && second_pass)
  					gf128mul_x_ble(&rctx->t, &t);
  				skcipher_walk_done(&w, avail - bs);
  				return 0;
  			}
  
  			le128_xor(wdst++, &t, wsrc++);
  			gf128mul_x_ble(&t, &t);
  		} while ((avail -= bs) >= bs);
  
  		err = skcipher_walk_done(&w, avail);
  	}
  
  	return err;
  }
  
  static int xor_tweak_pre(struct skcipher_request *req, bool enc)
  {
  	return xor_tweak(req, false, enc);
  }
  
  static int xor_tweak_post(struct skcipher_request *req, bool enc)
  {
  	return xor_tweak(req, true, enc);
  }
  
  static void cts_done(struct crypto_async_request *areq, int err)
  {
  	struct skcipher_request *req = areq->data;
  	le128 b;
  
  	if (!err) {
  		struct rctx *rctx = skcipher_request_ctx(req);
  
  		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
  		le128_xor(&b, &rctx->t, &b);
  		scatterwalk_map_and_copy(&b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
  	}
  
  	skcipher_request_complete(req, err);
  }
  
  static int cts_final(struct skcipher_request *req,
  		     int (*crypt)(struct skcipher_request *req))
  {
  	struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
  	int offset = req->cryptlen & ~(XTS_BLOCK_SIZE - 1);
  	struct rctx *rctx = skcipher_request_ctx(req);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int tail = req->cryptlen % XTS_BLOCK_SIZE;
  	le128 b[2];
  	int err;
  
  	rctx->tail = scatterwalk_ffwd(rctx->sg, req->dst,
  				      offset - XTS_BLOCK_SIZE);
  
  	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
  	memcpy(b + 1, b, tail);
  	scatterwalk_map_and_copy(b, req->src, offset, tail, 0);
  
  	le128_xor(b, &rctx->t, b);
  
  	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE + tail, 1);
  
  	skcipher_request_set_tfm(subreq, ctx->child);
  	skcipher_request_set_callback(subreq, req->base.flags, cts_done, req);
  	skcipher_request_set_crypt(subreq, rctx->tail, rctx->tail,
  				   XTS_BLOCK_SIZE, NULL);
  
  	err = crypt(subreq);
  	if (err)
  		return err;
  
  	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 0);
  	le128_xor(b, &rctx->t, b);
  	scatterwalk_map_and_copy(b, rctx->tail, 0, XTS_BLOCK_SIZE, 1);
  
  	return 0;
  }
  
  static void encrypt_done(struct crypto_async_request *areq, int err)
  {
  	struct skcipher_request *req = areq->data;
  
  	if (!err) {
  		struct rctx *rctx = skcipher_request_ctx(req);
  
  		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
  		err = xor_tweak_post(req, true);
  
  		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
  			err = cts_final(req, crypto_skcipher_encrypt);
  			if (err == -EINPROGRESS)
  				return;
  		}
  	}
  
  	skcipher_request_complete(req, err);
  }
  
  static void decrypt_done(struct crypto_async_request *areq, int err)
  {
  	struct skcipher_request *req = areq->data;
  
  	if (!err) {
  		struct rctx *rctx = skcipher_request_ctx(req);
  
  		rctx->subreq.base.flags &= ~CRYPTO_TFM_REQ_MAY_SLEEP;
  		err = xor_tweak_post(req, false);
  
  		if (!err && unlikely(req->cryptlen % XTS_BLOCK_SIZE)) {
  			err = cts_final(req, crypto_skcipher_decrypt);
  			if (err == -EINPROGRESS)
  				return;
  		}
  	}
  
  	skcipher_request_complete(req, err);
  }
  
  static int init_crypt(struct skcipher_request *req, crypto_completion_t compl)
  {
  	struct priv *ctx = crypto_skcipher_ctx(crypto_skcipher_reqtfm(req));
  	struct rctx *rctx = skcipher_request_ctx(req);
  	struct skcipher_request *subreq = &rctx->subreq;
  
  	if (req->cryptlen < XTS_BLOCK_SIZE)
  		return -EINVAL;
  
  	skcipher_request_set_tfm(subreq, ctx->child);
  	skcipher_request_set_callback(subreq, req->base.flags, compl, req);
  	skcipher_request_set_crypt(subreq, req->dst, req->dst,
  				   req->cryptlen & ~(XTS_BLOCK_SIZE - 1), NULL);
  
  	/* calculate first value of T */
  	crypto_cipher_encrypt_one(ctx->tweak, (u8 *)&rctx->t, req->iv);
  
  	return 0;
  }
  
  static int encrypt(struct skcipher_request *req)
  {
  	struct rctx *rctx = skcipher_request_ctx(req);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int err;
  
  	err = init_crypt(req, encrypt_done) ?:
  	      xor_tweak_pre(req, true) ?:
  	      crypto_skcipher_encrypt(subreq) ?:
  	      xor_tweak_post(req, true);
  
  	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
  		return err;
  
  	return cts_final(req, crypto_skcipher_encrypt);
  }
  
  static int decrypt(struct skcipher_request *req)
  {
  	struct rctx *rctx = skcipher_request_ctx(req);
  	struct skcipher_request *subreq = &rctx->subreq;
  	int err;
  
  	err = init_crypt(req, decrypt_done) ?:
  	      xor_tweak_pre(req, false) ?:
  	      crypto_skcipher_decrypt(subreq) ?:
  	      xor_tweak_post(req, false);
  
  	if (err || likely((req->cryptlen % XTS_BLOCK_SIZE) == 0))
  		return err;
  
  	return cts_final(req, crypto_skcipher_decrypt);
  }
  
  static int init_tfm(struct crypto_skcipher *tfm)
  {
  	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
  	struct xts_instance_ctx *ictx = skcipher_instance_ctx(inst);
  	struct priv *ctx = crypto_skcipher_ctx(tfm);
  	struct crypto_skcipher *child;
  	struct crypto_cipher *tweak;
  
  	child = crypto_spawn_skcipher(&ictx->spawn);
  	if (IS_ERR(child))
  		return PTR_ERR(child);
  
  	ctx->child = child;
  
  	tweak = crypto_alloc_cipher(ictx->name, 0, 0);
  	if (IS_ERR(tweak)) {
  		crypto_free_skcipher(ctx->child);
  		return PTR_ERR(tweak);
  	}
  
  	ctx->tweak = tweak;
  
  	crypto_skcipher_set_reqsize(tfm, crypto_skcipher_reqsize(child) +
  					 sizeof(struct rctx));
  
  	return 0;
  }
  
  static void exit_tfm(struct crypto_skcipher *tfm)
  {
  	struct priv *ctx = crypto_skcipher_ctx(tfm);
  
  	crypto_free_skcipher(ctx->child);
  	crypto_free_cipher(ctx->tweak);
  }
  
  static void crypto_xts_free(struct skcipher_instance *inst)
  {
  	crypto_drop_skcipher(skcipher_instance_ctx(inst));
  	kfree(inst);
  }
  
  static int create(struct crypto_template *tmpl, struct rtattr **tb)
  {
  	struct skcipher_instance *inst;
  	struct crypto_attr_type *algt;
  	struct xts_instance_ctx *ctx;
  	struct skcipher_alg *alg;
  	const char *cipher_name;
  	u32 mask;
  	int err;
  
  	algt = crypto_get_attr_type(tb);
  	if (IS_ERR(algt))
  		return PTR_ERR(algt);
  
  	if ((algt->type ^ CRYPTO_ALG_TYPE_SKCIPHER) & algt->mask)
  		return -EINVAL;
  
  	cipher_name = crypto_attr_alg_name(tb[1]);
  	if (IS_ERR(cipher_name))
  		return PTR_ERR(cipher_name);
  
  	inst = kzalloc(sizeof(*inst) + sizeof(*ctx), GFP_KERNEL);
  	if (!inst)
  		return -ENOMEM;
  
  	ctx = skcipher_instance_ctx(inst);
  
  	mask = crypto_requires_off(algt->type, algt->mask,
  				   CRYPTO_ALG_NEED_FALLBACK |
  				   CRYPTO_ALG_ASYNC);
  
  	err = crypto_grab_skcipher(&ctx->spawn, skcipher_crypto_instance(inst),
  				   cipher_name, 0, mask);
  	if (err == -ENOENT) {
  		err = -ENAMETOOLONG;
  		if (snprintf(ctx->name, CRYPTO_MAX_ALG_NAME, "ecb(%s)",
  			     cipher_name) >= CRYPTO_MAX_ALG_NAME)
  			goto err_free_inst;
  
  		err = crypto_grab_skcipher(&ctx->spawn,
  					   skcipher_crypto_instance(inst),
  					   ctx->name, 0, mask);
  	}
  
  	if (err)
  		goto err_free_inst;
  
  	alg = crypto_skcipher_spawn_alg(&ctx->spawn);
  
  	err = -EINVAL;
  	if (alg->base.cra_blocksize != XTS_BLOCK_SIZE)
  		goto err_free_inst;
  
  	if (crypto_skcipher_alg_ivsize(alg))
  		goto err_free_inst;
  
  	err = crypto_inst_setname(skcipher_crypto_instance(inst), "xts",
  				  &alg->base);
  	if (err)
  		goto err_free_inst;
  
  	err = -EINVAL;
  	cipher_name = alg->base.cra_name;
  
  	/* Alas we screwed up the naming so we have to mangle the
  	 * cipher name.
  	 */
  	if (!strncmp(cipher_name, "ecb(", 4)) {
  		unsigned len;
  
  		len = strlcpy(ctx->name, cipher_name + 4, sizeof(ctx->name));
  		if (len < 2 || len >= sizeof(ctx->name))
  			goto err_free_inst;
  
  		if (ctx->name[len - 1] != ')')
  			goto err_free_inst;
  
  		ctx->name[len - 1] = 0;
  
  		if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
  			     "xts(%s)", ctx->name) >= CRYPTO_MAX_ALG_NAME) {
  			err = -ENAMETOOLONG;
  			goto err_free_inst;
  		}
  	} else
  		goto err_free_inst;
  
  	inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
  	inst->alg.base.cra_priority = alg->base.cra_priority;
  	inst->alg.base.cra_blocksize = XTS_BLOCK_SIZE;
  	inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
  				       (__alignof__(u64) - 1);
  
  	inst->alg.ivsize = XTS_BLOCK_SIZE;
  	inst->alg.min_keysize = crypto_skcipher_alg_min_keysize(alg) * 2;
  	inst->alg.max_keysize = crypto_skcipher_alg_max_keysize(alg) * 2;
  
  	inst->alg.base.cra_ctxsize = sizeof(struct priv);
  
  	inst->alg.init = init_tfm;
  	inst->alg.exit = exit_tfm;
  
  	inst->alg.setkey = setkey;
  	inst->alg.encrypt = encrypt;
  	inst->alg.decrypt = decrypt;
  
  	inst->free = crypto_xts_free;
  
  	err = skcipher_register_instance(tmpl, inst);
  	if (err) {
  err_free_inst:
  		crypto_xts_free(inst);
  	}
  	return err;
  }
  
  static struct crypto_template crypto_tmpl = {
  	.name = "xts",
  	.create = create,
  	.module = THIS_MODULE,
  };
  
  static int __init crypto_module_init(void)
  {
  	return crypto_register_template(&crypto_tmpl);
  }
  
  static void __exit crypto_module_exit(void)
  {
  	crypto_unregister_template(&crypto_tmpl);
  }
  
  subsys_initcall(crypto_module_init);
  module_exit(crypto_module_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("XTS block cipher mode");
  MODULE_ALIAS_CRYPTO("xts");
  