/*
   * ECDH helper functions - KPP wrappings
   *
   * Copyright (C) 2017 Intel Corporation
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation;
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
   * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT OF THIRD PARTY RIGHTS.
   * IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) AND AUTHOR(S) BE LIABLE FOR ANY
   * CLAIM, OR ANY SPECIAL INDIRECT OR CONSEQUENTIAL DAMAGES, OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   *
   * ALL LIABILITY, INCLUDING LIABILITY FOR INFRINGEMENT OF ANY PATENTS,
   * COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS, RELATING TO USE OF THIS
   * SOFTWARE IS DISCLAIMED.
   */
  #include "ecdh_helper.h"

  #include <linux/scatterlist.h>

  #include <crypto/ecdh.h>
  
  struct ecdh_completion {
  	struct completion completion;
  	int err;
  };
  
  static void ecdh_complete(struct crypto_async_request *req, int err)
  {
  	struct ecdh_completion *res = req->data;
  
  	if (err == -EINPROGRESS)
  		return;
  
  	res->err = err;
  	complete(&res->completion);
  }
  
  static inline void swap_digits(u64 *in, u64 *out, unsigned int ndigits)
  {
  	int i;
  
  	for (i = 0; i < ndigits; i++)
  		out[i] = __swab64(in[ndigits - 1 - i]);
  }

  /* compute_ecdh_secret() - function assumes that the private key was
   *                         already set.
   * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
   * @public_key:   pair's ecc public key.
   * secret:        memory where the ecdh computed shared secret will be saved.
   *
   * Return: zero on success; error code in case of error.
   */

  int compute_ecdh_secret(struct crypto_kpp *tfm, const u8 public_key[64],

  			u8 secret[32])

  {

  	struct kpp_request *req;

  	u8 *tmp;

  	struct ecdh_completion result;
  	struct scatterlist src, dst;

  	int err;

  	tmp = kmalloc(64, GFP_KERNEL);
  	if (!tmp)

  		return -ENOMEM;

  	req = kpp_request_alloc(tfm, GFP_KERNEL);

  	if (!req) {
  		err = -ENOMEM;

  		goto free_tmp;

  	}

  
  	init_completion(&result.completion);

  	swap_digits((u64 *)public_key, (u64 *)tmp, 4); /* x */
  	swap_digits((u64 *)&public_key[32], (u64 *)&tmp[32], 4); /* y */
  
  	sg_init_one(&src, tmp, 64);
  	sg_init_one(&dst, secret, 32);
  	kpp_request_set_input(req, &src, 64);
  	kpp_request_set_output(req, &dst, 32);
  	kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
  				 ecdh_complete, &result);
  	err = crypto_kpp_compute_shared_secret(req);
  	if (err == -EINPROGRESS) {
  		wait_for_completion(&result.completion);
  		err = result.err;
  	}
  	if (err < 0) {
  		pr_err("alg: ecdh: compute shared secret failed. err %d
  ",
  		       err);
  		goto free_all;
  	}
  
  	swap_digits((u64 *)secret, (u64 *)tmp, 4);
  	memcpy(secret, tmp, 32);
  
  free_all:

  	kpp_request_free(req);

  free_tmp:

  	kfree_sensitive(tmp);

  	return err;

  }

  /* set_ecdh_privkey() - set or generate ecc private key.
   *
   * Function generates an ecc private key in the crypto subsystem when receiving
   * a NULL private key or sets the received key when not NULL.
   *
   * @tfm:           KPP tfm handle allocated with crypto_alloc_kpp().
   * @private_key:   user's ecc private key. When not NULL, the key is expected
   *                 in little endian format.
   *
   * Return: zero on success; error code in case of error.
   */
  int set_ecdh_privkey(struct crypto_kpp *tfm, const u8 private_key[32])
  {
  	u8 *buf, *tmp = NULL;
  	unsigned int buf_len;
  	int err;
  	struct ecdh p = {0};
  
  	p.curve_id = ECC_CURVE_NIST_P256;
  
  	if (private_key) {
  		tmp = kmalloc(32, GFP_KERNEL);
  		if (!tmp)
  			return -ENOMEM;
  		swap_digits((u64 *)private_key, (u64 *)tmp, 4);
  		p.key = tmp;
  		p.key_size = 32;
  	}
  
  	buf_len = crypto_ecdh_key_len(&p);
  	buf = kmalloc(buf_len, GFP_KERNEL);
  	if (!buf) {
  		err = -ENOMEM;
  		goto free_tmp;
  	}
  
  	err = crypto_ecdh_encode_key(buf, buf_len, &p);
  	if (err)
  		goto free_all;
  
  	err = crypto_kpp_set_secret(tfm, buf, buf_len);
  	/* fall through */
  free_all:

  	kfree_sensitive(buf);

  free_tmp:

  	kfree_sensitive(tmp);

  	return err;
  }
  
  /* generate_ecdh_public_key() - function assumes that the private key was
   *                              already set.
   *
   * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
   * @public_key:   memory where the computed ecc public key will be saved.
   *
   * Return: zero on success; error code in case of error.
   */
  int generate_ecdh_public_key(struct crypto_kpp *tfm, u8 public_key[64])

  {

  	struct kpp_request *req;

  	u8 *tmp;

  	struct ecdh_completion result;
  	struct scatterlist dst;

  	int err;

  	tmp = kmalloc(64, GFP_KERNEL);
  	if (!tmp)

  		return -ENOMEM;

  	req = kpp_request_alloc(tfm, GFP_KERNEL);

  	if (!req) {
  		err = -ENOMEM;

  		goto free_tmp;

  	}

  
  	init_completion(&result.completion);

  	sg_init_one(&dst, tmp, 64);
  	kpp_request_set_input(req, NULL, 0);
  	kpp_request_set_output(req, &dst, 64);
  	kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
  				 ecdh_complete, &result);

  	err = crypto_kpp_generate_public_key(req);
  	if (err == -EINPROGRESS) {
  		wait_for_completion(&result.completion);
  		err = result.err;
  	}
  	if (err < 0)
  		goto free_all;
  
  	/* The public key is handed back in little endian as expected by
  	 * the Security Manager Protocol.

  	 */
  	swap_digits((u64 *)tmp, (u64 *)public_key, 4); /* x */
  	swap_digits((u64 *)&tmp[32], (u64 *)&public_key[32], 4); /* y */

  
  free_all:

  	kpp_request_free(req);

  free_tmp:
  	kfree(tmp);

  	return err;

  }

  
  /* generate_ecdh_keys() - generate ecc key pair.
   *
   * @tfm:          KPP tfm handle allocated with crypto_alloc_kpp().
   * @public_key:   memory where the computed ecc public key will be saved.
   *
   * Return: zero on success; error code in case of error.
   */
  int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64])
  {
  	int err;
  
  	err = set_ecdh_privkey(tfm, NULL);
  	if (err)
  		return err;
  
  	return generate_ecdh_public_key(tfm, public_key);
  }