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linux-stable/security/keys/trusted-keys/trusted_dcp.c

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// 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;
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, NULL,
NULL);
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_aead_encrypt(aead_req);
else
ret = crypto_aead_decrypt(aead_req);
free_req:
aead_request_free(aead_req);
free_aead:
crypto_free_aead(aead);
out:
return ret;
}
static int decrypt_blob_key(u8 *key)
{
return do_dcp_crypto(key, key, false);
}
static int encrypt_blob_key(u8 *key)
{
return do_dcp_crypto(key, 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;
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(b->blob_key, AES_KEYSIZE_128);
ret = do_aead_crypto(p->key, b->payload, p->key_len, b->blob_key,
b->nonce, true);
if (ret) {
pr_err("Unable to encrypt blob payload: %i\n", ret);
return ret;
}
ret = encrypt_blob_key(b->blob_key);
if (ret) {
pr_err("Unable to encrypt blob key: %i\n", ret);
return ret;
}
b->payload_len = get_unaligned_le32(&p->key_len);
p->blob_len = blen;
return 0;
}
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;
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);
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,
b->blob_key, b->nonce, false);
if (ret) {
pr_err("Unwrap of DCP payload failed: %i\n", ret);
goto out;
}
ret = 0;
out:
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,
};
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