KEYS: asym_tpm: Implement encryption operation [ver #2]

This patch impelements the pkey_encrypt operation.  The public key
portion extracted from the TPM key blob is used.  The operation is
performed entirely in software using the crypto API.
Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

crypto/asymmetric_keys/asym_tpm.c

@@ -165,6 +165,8 @@ static int tpm_key_query(const struct kernel_pkey_params *params,
 	info->max_enc_size = len;
 	info->max_dec_size = tk->key_len / 8;
 
+	info->supported_ops = KEYCTL_SUPPORTS_ENCRYPT;
+
 	ret = 0;
 error_free_tfm:
 	crypto_free_akcipher(tfm);
@@ -172,6 +174,87 @@ static int tpm_key_query(const struct kernel_pkey_params *params,
 	return ret;
 }
 
+/*
+ * Encryption operation is performed with the public key.  Hence it is done
+ * in software
+ */
+static int tpm_key_encrypt(struct tpm_key *tk,
+			   struct kernel_pkey_params *params,
+			   const void *in, void *out)
+{
+	char alg_name[CRYPTO_MAX_ALG_NAME];
+	struct crypto_akcipher *tfm;
+	struct akcipher_request *req;
+	struct crypto_wait cwait;
+	struct scatterlist in_sg, out_sg;
+	uint8_t der_pub_key[PUB_KEY_BUF_SIZE];
+	uint32_t der_pub_key_len;
+	int ret;
+
+	pr_devel("==>%s()\n", __func__);
+
+	ret = determine_akcipher(params->encoding, params->hash_algo, alg_name);
+	if (ret < 0)
+		return ret;
+
+	tfm = crypto_alloc_akcipher(alg_name, 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	der_pub_key_len = derive_pub_key(tk->pub_key, tk->pub_key_len,
+					 der_pub_key);
+
+	ret = crypto_akcipher_set_pub_key(tfm, der_pub_key, der_pub_key_len);
+	if (ret < 0)
+		goto error_free_tfm;
+
+	req = akcipher_request_alloc(tfm, GFP_KERNEL);
+	if (!req)
+		goto error_free_tfm;
+
+	sg_init_one(&in_sg, in, params->in_len);
+	sg_init_one(&out_sg, out, params->out_len);
+	akcipher_request_set_crypt(req, &in_sg, &out_sg, params->in_len,
+				   params->out_len);
+	crypto_init_wait(&cwait);
+	akcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
+				      CRYPTO_TFM_REQ_MAY_SLEEP,
+				      crypto_req_done, &cwait);
+
+	ret = crypto_akcipher_encrypt(req);
+	ret = crypto_wait_req(ret, &cwait);
+
+	if (ret == 0)
+		ret = req->dst_len;
+
+	akcipher_request_free(req);
+error_free_tfm:
+	crypto_free_akcipher(tfm);
+	pr_devel("<==%s() = %d\n", __func__, ret);
+	return ret;
+}
+
+/*
+ * Do encryption, decryption and signing ops.
+ */
+static int tpm_key_eds_op(struct kernel_pkey_params *params,
+			  const void *in, void *out)
+{
+	struct tpm_key *tk = params->key->payload.data[asym_crypto];
+	int ret = -EOPNOTSUPP;
+
+	/* Perform the encryption calculation. */
+	switch (params->op) {
+	case kernel_pkey_encrypt:
+		ret = tpm_key_encrypt(tk, params, in, out);
+		break;
+	default:
+		BUG();
+	}
+
+	return ret;
+}
+
 /*
  * Parse enough information out of TPM_KEY structure:
  * TPM_STRUCT_VER -> 4 bytes
@@ -329,6 +412,7 @@ struct asymmetric_key_subtype asym_tpm_subtype = {
 	.describe		= asym_tpm_describe,
 	.destroy		= asym_tpm_destroy,
 	.query			= tpm_key_query,
+	.eds_op			= tpm_key_eds_op,
 };
 EXPORT_SYMBOL_GPL(asym_tpm_subtype);