security/keys/trusted-keys/trusted_dcp.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2021 sigma star gmbh
  */

 #include <crypto/aead.h>
 #include <crypto/aes.h>
 #include <crypto/algapi.h>
 #include <crypto/gcm.h>
 #include <crypto/skcipher.h>
 #include <keys/trusted-type.h>
 #include <linux/key-type.h>
 #include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/random.h>
 #include <linux/scatterlist.h>
 #include <soc/fsl/dcp.h>

 #define DCP_BLOB_VERSION 1
 #define DCP_BLOB_AUTHLEN 16

 /**
  * DOC: dcp blob format
  *
  * The Data Co-Processor (DCP) provides hardware-bound AES keys using its
  * AES encryption engine only. It does not provide direct key sealing/unsealing.
  * To make DCP hardware encryption keys usable as trust source, we define
  * our own custom format that uses a hardware-bound key to secure the sealing
  * key stored in the key blob.
  *
  * Whenever a new trusted key using DCP is generated, we generate a random 128-bit
  * blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
  * encrypt the trusted key payload using AES-128-GCM.
  *
  * The BEK itself is encrypted using the hardware-bound key using the DCP's AES
  * encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
  * BEK-encrypted payload and authentication tag make up the blob format together
  * with a version number, payload length and authentication tag.
  */

 /**
  * struct dcp_blob_fmt - DCP BLOB format.
  *
  * @fmt_version: Format version, currently being %1.
  * @blob_key: Random AES 128 key which is used to encrypt @payload,
  *            @blob_key itself is encrypted with OTP or UNIQUE device key in
  *            AES-128-ECB mode by DCP.
  * @nonce: Random nonce used for @payload encryption.
  * @payload_len: Length of the plain text @payload.
  * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
  *           GCM auth tag of size DCP_BLOB_AUTHLEN is attached at the end of it.
  *
  * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
  * DCP_BLOB_AUTHLEN.
  */
 struct dcp_blob_fmt {
 	__u8 fmt_version;
 	__u8 blob_key[AES_KEYSIZE_128];
 	__u8 nonce[AES_KEYSIZE_128];
 	__le32 payload_len;
 	__u8 payload[];
 } __packed;

 static bool use_otp_key;
 module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
 MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");

 static bool skip_zk_test;
 module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
 MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are zero'ed");

 static unsigned int calc_blob_len(unsigned int payload_len)
 {
 	return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
 }

 static int do_dcp_crypto(u8 *in, u8 *out, bool do_encrypt)
 {
 	struct skcipher_request *req = NULL;
 	struct scatterlist src_sg, dst_sg;
 	struct crypto_skcipher *tfm;
 	u8 paes_key[DCP_PAES_KEYSIZE];
 	DECLARE_CRYPTO_WAIT(wait);
 	int res = 0;

 	if (use_otp_key)
 		paes_key[0] = DCP_PAES_KEY_OTP;
 	else
 		paes_key[0] = DCP_PAES_KEY_UNIQUE;

 	tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
 				    CRYPTO_ALG_INTERNAL);
 	if (IS_ERR(tfm)) {
 		res = PTR_ERR(tfm);
 		tfm = NULL;
 		goto out;
 	}

 	req = skcipher_request_alloc(tfm, GFP_NOFS);
 	if (!req) {
 		res = -ENOMEM;
 		goto out;
 	}

 	skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
 				      CRYPTO_TFM_REQ_MAY_SLEEP,
 				      crypto_req_done, &wait);
 	res = crypto_skcipher_setkey(tfm, paes_key, sizeof(paes_key));
 	if (res < 0)
 		goto out;

 	sg_init_one(&src_sg, in, AES_KEYSIZE_128);
 	sg_init_one(&dst_sg, out, AES_KEYSIZE_128);
 	skcipher_request_set_crypt(req, &src_sg, &dst_sg, AES_KEYSIZE_128,
 				   NULL);

 	if (do_encrypt)
 		res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
 	else
 		res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);

 out:
 	skcipher_request_free(req);
 	crypto_free_skcipher(tfm);

 	return res;
 }

 static int do_aead_crypto(u8 *in, u8 *out, size_t len, u8 *key, u8 *nonce,
 			  bool do_encrypt)
 {
 	struct aead_request *aead_req = NULL;
 	struct scatterlist src_sg, dst_sg;
 	struct crypto_aead *aead;
 	int ret;
 	DECLARE_CRYPTO_WAIT(wait);

 	aead = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
 	if (IS_ERR(aead)) {
 		ret = PTR_ERR(aead);
 		goto out;
 	}

 	ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
 	if (ret < 0) {
 		pr_err("Can't set crypto auth tag len: %d\n", ret);
 		goto free_aead;
 	}

 	aead_req = aead_request_alloc(aead, GFP_KERNEL);
 	if (!aead_req) {
 		ret = -ENOMEM;
 		goto free_aead;
 	}

 	sg_init_one(&src_sg, in, len);
 	if (do_encrypt) {
 		/*
 		 * If we encrypt our buffer has extra space for the auth tag.
 		 */
 		sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
 	} else {
 		sg_init_one(&dst_sg, out, len);
 	}

 	aead_request_set_crypt(aead_req, &src_sg, &dst_sg, len, nonce);
 	aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP,
 				  crypto_req_done, &wait);
 	aead_request_set_ad(aead_req, 0);

 	if (crypto_aead_setkey(aead, key, AES_KEYSIZE_128)) {
 		pr_err("Can't set crypto AEAD key\n");
 		ret = -EINVAL;
 		goto free_req;
 	}

 	if (do_encrypt)
 		ret = crypto_wait_req(crypto_aead_encrypt(aead_req), &wait);
 	else
 		ret = crypto_wait_req(crypto_aead_decrypt(aead_req), &wait);

 free_req:
 	aead_request_free(aead_req);
 free_aead:
 	crypto_free_aead(aead);
 out:
 	return ret;
 }

 static int decrypt_blob_key(u8 *encrypted_key, u8 *plain_key)
 {
 	return do_dcp_crypto(encrypted_key, plain_key, false);
 }

 static int encrypt_blob_key(u8 *plain_key, u8 *encrypted_key)
 {
 	return do_dcp_crypto(plain_key, encrypted_key, true);
 }

 static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
 {
 	struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
 	int blen, ret;
 	u8 plain_blob_key[AES_KEYSIZE_128];

 	blen = calc_blob_len(p->key_len);
 	if (blen > MAX_BLOB_SIZE)
 		return -E2BIG;

 	b->fmt_version = DCP_BLOB_VERSION;
 	get_random_bytes(b->nonce, AES_KEYSIZE_128);
 	get_random_bytes(plain_blob_key, AES_KEYSIZE_128);

 	ret = do_aead_crypto(p->key, b->payload, p->key_len, plain_blob_key,
 			     b->nonce, true);
 	if (ret) {
 		pr_err("Unable to encrypt blob payload: %i\n", ret);
 		goto out;
 	}

 	ret = encrypt_blob_key(plain_blob_key, b->blob_key);
 	if (ret) {
 		pr_err("Unable to encrypt blob key: %i\n", ret);
 		goto out;
 	}

 	put_unaligned_le32(p->key_len, &b->payload_len);
 	p->blob_len = blen;
 	ret = 0;

 out:
 	memzero_explicit(plain_blob_key, sizeof(plain_blob_key));

 	return ret;
 }

 static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
 {
 	struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
 	int blen, ret;
 	u8 plain_blob_key[AES_KEYSIZE_128];

 	if (b->fmt_version != DCP_BLOB_VERSION) {
 		pr_err("DCP blob has bad version: %i, expected %i\n",
 		       b->fmt_version, DCP_BLOB_VERSION);
 		ret = -EINVAL;
 		goto out;
 	}

 	p->key_len = le32_to_cpu(b->payload_len);
 	blen = calc_blob_len(p->key_len);
 	if (blen != p->blob_len) {
 		pr_err("DCP blob has bad length: %i != %i\n", blen,
 		       p->blob_len);
 		ret = -EINVAL;
 		goto out;
 	}

 	ret = decrypt_blob_key(b->blob_key, plain_blob_key);
 	if (ret) {
 		pr_err("Unable to decrypt blob key: %i\n", ret);
 		goto out;
 	}

 	ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
 			     plain_blob_key, b->nonce, false);
 	if (ret) {
 		pr_err("Unwrap of DCP payload failed: %i\n", ret);
 		goto out;
 	}

 	ret = 0;
 out:
 	memzero_explicit(plain_blob_key, sizeof(plain_blob_key));

 	return ret;
 }

 static int test_for_zero_key(void)
 {
 	/*
 	 * Encrypting a plaintext of all 0x55 bytes will yield
 	 * this ciphertext in case the DCP test key is used.
 	 */
 	static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff,
 				 0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f};
 	void *buf = NULL;
 	int ret = 0;

 	if (skip_zk_test)
 		goto out;

 	buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
 	if (!buf) {
 		ret = -ENOMEM;
 		goto out;
 	}

 	memset(buf, 0x55, AES_BLOCK_SIZE);

 	ret = do_dcp_crypto(buf, buf, true);
 	if (ret)
 		goto out;

 	if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
 		pr_warn("Device neither in secure nor trusted mode!\n");
 		ret = -EINVAL;
 	}
 out:
 	kfree(buf);
 	return ret;
 }

 static int trusted_dcp_init(void)
 {
 	int ret;

 	if (use_otp_key)
 		pr_info("Using DCP OTP key\n");

 	ret = test_for_zero_key();
 	if (ret) {
 		pr_warn("Test for zero'ed keys failed: %i\n", ret);

 		return -EINVAL;
 	}

 	return register_key_type(&key_type_trusted);
 }

 static void trusted_dcp_exit(void)
 {
 	unregister_key_type(&key_type_trusted);
 }

 struct trusted_key_ops dcp_trusted_key_ops = {
 	.exit = trusted_dcp_exit,
 	.init = trusted_dcp_init,
 	.seal = trusted_dcp_seal,
 	.unseal = trusted_dcp_unseal,
 	.migratable = 0,
 };
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Copyright (C) 2021 sigma star gmbh
	*/

	#include <crypto/aead.h>
	#include <crypto/aes.h>
	#include <crypto/algapi.h>
	#include <crypto/gcm.h>
	#include <crypto/skcipher.h>
	#include <keys/trusted-type.h>
	#include <linux/key-type.h>
	#include <linux/module.h>
	#include <linux/printk.h>
	#include <linux/random.h>
	#include <linux/scatterlist.h>
	#include <soc/fsl/dcp.h>

	#define DCP_BLOB_VERSION 1
	#define DCP_BLOB_AUTHLEN 16

	/**
	* DOC: dcp blob format
	*
	* The Data Co-Processor (DCP) provides hardware-bound AES keys using its
	* AES encryption engine only. It does not provide direct key sealing/unsealing.
	* To make DCP hardware encryption keys usable as trust source, we define
	* our own custom format that uses a hardware-bound key to secure the sealing
	* key stored in the key blob.
	*
	* Whenever a new trusted key using DCP is generated, we generate a random 128-bit
	* blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
	* encrypt the trusted key payload using AES-128-GCM.
	*
	* The BEK itself is encrypted using the hardware-bound key using the DCP's AES
	* encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
	* BEK-encrypted payload and authentication tag make up the blob format together
	* with a version number, payload length and authentication tag.
	*/

	/**
	* struct dcp_blob_fmt - DCP BLOB format.
	*
	* @fmt_version: Format version, currently being %1.
	* @blob_key: Random AES 128 key which is used to encrypt @payload,
	* @blob_key itself is encrypted with OTP or UNIQUE device key in
	* AES-128-ECB mode by DCP.
	* @nonce: Random nonce used for @payload encryption.
	* @payload_len: Length of the plain text @payload.
	* @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
	* GCM auth tag of size DCP_BLOB_AUTHLEN is attached at the end of it.
	*
	* The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
	* DCP_BLOB_AUTHLEN.
	*/
	struct dcp_blob_fmt {
	__u8 fmt_version;
	__u8 blob_key[AES_KEYSIZE_128];
	__u8 nonce[AES_KEYSIZE_128];
	__le32 payload_len;
	__u8 payload[];
	} __packed;

	static bool use_otp_key;
	module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
	MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");

	static bool skip_zk_test;
	module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
	MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are zero'ed");

	static unsigned int calc_blob_len(unsigned int payload_len)
	{
	return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
	}

	static int do_dcp_crypto(u8 in, u8 out, bool do_encrypt)
	{
	struct skcipher_request *req = NULL;
	struct scatterlist src_sg, dst_sg;
	struct crypto_skcipher *tfm;
	u8 paes_key[DCP_PAES_KEYSIZE];
	DECLARE_CRYPTO_WAIT(wait);
	int res = 0;

	if (use_otp_key)
	paes_key[0] = DCP_PAES_KEY_OTP;
	else
	paes_key[0] = DCP_PAES_KEY_UNIQUE;

	tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
	CRYPTO_ALG_INTERNAL);
	if (IS_ERR(tfm)) {
	res = PTR_ERR(tfm);
	tfm = NULL;
	goto out;
	}

	req = skcipher_request_alloc(tfm, GFP_NOFS);
	if (!req) {
	res = -ENOMEM;
	goto out;
	}

	skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG \|
	CRYPTO_TFM_REQ_MAY_SLEEP,
	crypto_req_done, &wait);
	res = crypto_skcipher_setkey(tfm, paes_key, sizeof(paes_key));
	if (res < 0)
	goto out;

	sg_init_one(&src_sg, in, AES_KEYSIZE_128);
	sg_init_one(&dst_sg, out, AES_KEYSIZE_128);
	skcipher_request_set_crypt(req, &src_sg, &dst_sg, AES_KEYSIZE_128,
	NULL);

	if (do_encrypt)
	res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
	else
	res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);

	out:
	skcipher_request_free(req);
	crypto_free_skcipher(tfm);

	return res;
	}

	static int do_aead_crypto(u8 in, u8 out, size_t len, u8 key, u8 nonce,
	bool do_encrypt)
	{
	struct aead_request *aead_req = NULL;
	struct scatterlist src_sg, dst_sg;
	struct crypto_aead *aead;
	int ret;
	DECLARE_CRYPTO_WAIT(wait);

	aead = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
	if (IS_ERR(aead)) {
	ret = PTR_ERR(aead);
	goto out;
	}

	ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
	if (ret < 0) {
	pr_err("Can't set crypto auth tag len: %d\n", ret);
	goto free_aead;
	}

	aead_req = aead_request_alloc(aead, GFP_KERNEL);
	if (!aead_req) {
	ret = -ENOMEM;
	goto free_aead;
	}

	sg_init_one(&src_sg, in, len);
	if (do_encrypt) {
	/*
	* If we encrypt our buffer has extra space for the auth tag.
	*/
	sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
	} else {
	sg_init_one(&dst_sg, out, len);
	}

	aead_request_set_crypt(aead_req, &src_sg, &dst_sg, len, nonce);
	aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP,
	crypto_req_done, &wait);
	aead_request_set_ad(aead_req, 0);

	if (crypto_aead_setkey(aead, key, AES_KEYSIZE_128)) {
	pr_err("Can't set crypto AEAD key\n");
	ret = -EINVAL;
	goto free_req;
	}

	if (do_encrypt)
	ret = crypto_wait_req(crypto_aead_encrypt(aead_req), &wait);
	else
	ret = crypto_wait_req(crypto_aead_decrypt(aead_req), &wait);

	free_req:
	aead_request_free(aead_req);
	free_aead:
	crypto_free_aead(aead);
	out:
	return ret;
	}

	static int decrypt_blob_key(u8 encrypted_key, u8 plain_key)
	{
	return do_dcp_crypto(encrypted_key, plain_key, false);
	}

	static int encrypt_blob_key(u8 plain_key, u8 encrypted_key)
	{
	return do_dcp_crypto(plain_key, encrypted_key, true);
	}

	static int trusted_dcp_seal(struct trusted_key_payload p, char datablob)
	{
	struct dcp_blob_fmt b = (struct dcp_blob_fmt )p->blob;
	int blen, ret;
	u8 plain_blob_key[AES_KEYSIZE_128];

	blen = calc_blob_len(p->key_len);
	if (blen > MAX_BLOB_SIZE)
	return -E2BIG;

	b->fmt_version = DCP_BLOB_VERSION;
	get_random_bytes(b->nonce, AES_KEYSIZE_128);
	get_random_bytes(plain_blob_key, AES_KEYSIZE_128);

	ret = do_aead_crypto(p->key, b->payload, p->key_len, plain_blob_key,
	b->nonce, true);
	if (ret) {
	pr_err("Unable to encrypt blob payload: %i\n", ret);
	goto out;
	}

	ret = encrypt_blob_key(plain_blob_key, b->blob_key);
	if (ret) {
	pr_err("Unable to encrypt blob key: %i\n", ret);
	goto out;
	}

	put_unaligned_le32(p->key_len, &b->payload_len);
	p->blob_len = blen;
	ret = 0;

	out:
	memzero_explicit(plain_blob_key, sizeof(plain_blob_key));

	return ret;
	}

	static int trusted_dcp_unseal(struct trusted_key_payload p, char datablob)
	{
	struct dcp_blob_fmt b = (struct dcp_blob_fmt )p->blob;
	int blen, ret;
	u8 plain_blob_key[AES_KEYSIZE_128];

	if (b->fmt_version != DCP_BLOB_VERSION) {
	pr_err("DCP blob has bad version: %i, expected %i\n",
	b->fmt_version, DCP_BLOB_VERSION);
	ret = -EINVAL;
	goto out;
	}

	p->key_len = le32_to_cpu(b->payload_len);
	blen = calc_blob_len(p->key_len);
	if (blen != p->blob_len) {
	pr_err("DCP blob has bad length: %i != %i\n", blen,
	p->blob_len);
	ret = -EINVAL;
	goto out;
	}

	ret = decrypt_blob_key(b->blob_key, plain_blob_key);
	if (ret) {
	pr_err("Unable to decrypt blob key: %i\n", ret);
	goto out;
	}

	ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
	plain_blob_key, b->nonce, false);
	if (ret) {
	pr_err("Unwrap of DCP payload failed: %i\n", ret);
	goto out;
	}

	ret = 0;
	out:
	memzero_explicit(plain_blob_key, sizeof(plain_blob_key));

	return ret;
	}

	static int test_for_zero_key(void)
	{
	/*
	* Encrypting a plaintext of all 0x55 bytes will yield
	* this ciphertext in case the DCP test key is used.
	*/
	static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff,
	0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f};
	void *buf = NULL;
	int ret = 0;

	if (skip_zk_test)
	goto out;

	buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
	if (!buf) {
	ret = -ENOMEM;
	goto out;
	}

	memset(buf, 0x55, AES_BLOCK_SIZE);

	ret = do_dcp_crypto(buf, buf, true);
	if (ret)
	goto out;

	if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
	pr_warn("Device neither in secure nor trusted mode!\n");
	ret = -EINVAL;
	}
	out:
	kfree(buf);
	return ret;
	}

	static int trusted_dcp_init(void)
	{
	int ret;

	if (use_otp_key)
	pr_info("Using DCP OTP key\n");

	ret = test_for_zero_key();
	if (ret) {
	pr_warn("Test for zero'ed keys failed: %i\n", ret);

	return -EINVAL;
	}

	return register_key_type(&key_type_trusted);
	}

	static void trusted_dcp_exit(void)
	{
	unregister_key_type(&key_type_trusted);
	}

	struct trusted_key_ops dcp_trusted_key_ops = {
	.exit = trusted_dcp_exit,
	.init = trusted_dcp_init,
	.seal = trusted_dcp_seal,
	.unseal = trusted_dcp_unseal,
	.migratable = 0,
	};