security/keys/trusted-keys/trusted_dcp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2021 sigma star gmbh
   4  */
   5
   6 #include <crypto/aead.h>
   7 #include <crypto/aes.h>
   8 #include <crypto/algapi.h>
   9 #include <crypto/gcm.h>
  10 #include <crypto/skcipher.h>
  11 #include <keys/trusted-type.h>
  12 #include <linux/key-type.h>
  13 #include <linux/module.h>
  14 #include <linux/printk.h>
  15 #include <linux/random.h>
  16 #include <linux/scatterlist.h>
  17 #include <soc/fsl/dcp.h>
  18
  19 #define DCP_BLOB_VERSION 1
  20 #define DCP_BLOB_AUTHLEN 16
  21
  22 /**
  23  * DOC: dcp blob format
  24  *
  25  * The Data Co-Processor (DCP) provides hardware-bound AES keys using its
  26  * AES encryption engine only. It does not provide direct key sealing/unsealing.
  27  * To make DCP hardware encryption keys usable as trust source, we define
  28  * our own custom format that uses a hardware-bound key to secure the sealing
  29  * key stored in the key blob.
  30  *
  31  * Whenever a new trusted key using DCP is generated, we generate a random 128-bit
  32  * blob encryption key (BEK) and 128-bit nonce. The BEK and nonce are used to
  33  * encrypt the trusted key payload using AES-128-GCM.
  34  *
  35  * The BEK itself is encrypted using the hardware-bound key using the DCP's AES
  36  * encryption engine with AES-128-ECB. The encrypted BEK, generated nonce,
  37  * BEK-encrypted payload and authentication tag make up the blob format together
  38  * with a version number, payload length and authentication tag.
  39  */
  40
  41 /**
  42  * struct dcp_blob_fmt - DCP BLOB format.
  43  *
  44  * @fmt_version: Format version, currently being %1.
  45  * @blob_key: Random AES 128 key which is used to encrypt @payload,
  46  *            @blob_key itself is encrypted with OTP or UNIQUE device key in
  47  *            AES-128-ECB mode by DCP.
  48  * @nonce: Random nonce used for @payload encryption.
  49  * @payload_len: Length of the plain text @payload.
  50  * @payload: The payload itself, encrypted using AES-128-GCM and @blob_key,
  51  *           GCM auth tag of size DCP_BLOB_AUTHLEN is attached at the end of it.
  52  *
  53  * The total size of a DCP BLOB is sizeof(struct dcp_blob_fmt) + @payload_len +
  54  * DCP_BLOB_AUTHLEN.
  55  */
  56 struct dcp_blob_fmt {
  57         __u8 fmt_version;
  58         __u8 blob_key[AES_KEYSIZE_128];
  59         __u8 nonce[AES_KEYSIZE_128];
  60         __le32 payload_len;
  61         __u8 payload[];
  62 } __packed;
  63
  64 static bool use_otp_key;
  65 module_param_named(dcp_use_otp_key, use_otp_key, bool, 0);
  66 MODULE_PARM_DESC(dcp_use_otp_key, "Use OTP instead of UNIQUE key for sealing");
  67
  68 static bool skip_zk_test;
  69 module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
  70 MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are zero'ed");
  71
  72 static unsigned int calc_blob_len(unsigned int payload_len)
  73 {
  74         return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
  75 }
  76
  77 static int do_dcp_crypto(u8 *in, u8 *out, bool do_encrypt)
  78 {
  79         struct skcipher_request *req = NULL;
  80         struct scatterlist src_sg, dst_sg;
  81         struct crypto_skcipher *tfm;
  82         u8 paes_key[DCP_PAES_KEYSIZE];
  83         DECLARE_CRYPTO_WAIT(wait);
  84         int res = 0;
  85
  86         if (use_otp_key)
  87                 paes_key[0] = DCP_PAES_KEY_OTP;
  88         else
  89                 paes_key[0] = DCP_PAES_KEY_UNIQUE;
  90
  91         tfm = crypto_alloc_skcipher("ecb-paes-dcp", CRYPTO_ALG_INTERNAL,
  92                                     CRYPTO_ALG_INTERNAL);
  93         if (IS_ERR(tfm)) {
  94                 res = PTR_ERR(tfm);
  95                 tfm = NULL;
  96                 goto out;
  97         }
  98
  99         req = skcipher_request_alloc(tfm, GFP_NOFS);
 100         if (!req) {
 101                 res = -ENOMEM;
 102                 goto out;
 103         }
 104
 105         skcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
 106                                       CRYPTO_TFM_REQ_MAY_SLEEP,
 107                                       crypto_req_done, &wait);
 108         res = crypto_skcipher_setkey(tfm, paes_key, sizeof(paes_key));
 109         if (res < 0)
 110                 goto out;
 111
 112         sg_init_one(&src_sg, in, AES_KEYSIZE_128);
 113         sg_init_one(&dst_sg, out, AES_KEYSIZE_128);
 114         skcipher_request_set_crypt(req, &src_sg, &dst_sg, AES_KEYSIZE_128,
 115                                    NULL);
 116
 117         if (do_encrypt)
 118                 res = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
 119         else
 120                 res = crypto_wait_req(crypto_skcipher_decrypt(req), &wait);
 121
 122 out:
 123         skcipher_request_free(req);
 124         crypto_free_skcipher(tfm);
 125
 126         return res;
 127 }
 128
 129 static int do_aead_crypto(u8 *in, u8 *out, size_t len, u8 *key, u8 *nonce,
 130                           bool do_encrypt)
 131 {
 132         struct aead_request *aead_req = NULL;
 133         struct scatterlist src_sg, dst_sg;
 134         struct crypto_aead *aead;
 135         int ret;
 136         DECLARE_CRYPTO_WAIT(wait);
 137
 138         aead = crypto_alloc_aead("gcm(aes)", 0, CRYPTO_ALG_ASYNC);
 139         if (IS_ERR(aead)) {
 140                 ret = PTR_ERR(aead);
 141                 goto out;
 142         }
 143
 144         ret = crypto_aead_setauthsize(aead, DCP_BLOB_AUTHLEN);
 145         if (ret < 0) {
 146                 pr_err("Can't set crypto auth tag len: %d\n", ret);
 147                 goto free_aead;
 148         }
 149
 150         aead_req = aead_request_alloc(aead, GFP_KERNEL);
 151         if (!aead_req) {
 152                 ret = -ENOMEM;
 153                 goto free_aead;
 154         }
 155
 156         sg_init_one(&src_sg, in, len);
 157         if (do_encrypt) {
 158                 /*
 159                  * If we encrypt our buffer has extra space for the auth tag.
 160                  */
 161                 sg_init_one(&dst_sg, out, len + DCP_BLOB_AUTHLEN);
 162         } else {
 163                 sg_init_one(&dst_sg, out, len);
 164         }
 165
 166         aead_request_set_crypt(aead_req, &src_sg, &dst_sg, len, nonce);
 167         aead_request_set_callback(aead_req, CRYPTO_TFM_REQ_MAY_SLEEP,
 168                                   crypto_req_done, &wait);
 169         aead_request_set_ad(aead_req, 0);
 170
 171         if (crypto_aead_setkey(aead, key, AES_KEYSIZE_128)) {
 172                 pr_err("Can't set crypto AEAD key\n");
 173                 ret = -EINVAL;
 174                 goto free_req;
 175         }
 176
 177         if (do_encrypt)
 178                 ret = crypto_wait_req(crypto_aead_encrypt(aead_req), &wait);
 179         else
 180                 ret = crypto_wait_req(crypto_aead_decrypt(aead_req), &wait);
 181
 182 free_req:
 183         aead_request_free(aead_req);
 184 free_aead:
 185         crypto_free_aead(aead);
 186 out:
 187         return ret;
 188 }
 189
 190 static int decrypt_blob_key(u8 *encrypted_key, u8 *plain_key)
 191 {
 192         return do_dcp_crypto(encrypted_key, plain_key, false);
 193 }
 194
 195 static int encrypt_blob_key(u8 *plain_key, u8 *encrypted_key)
 196 {
 197         return do_dcp_crypto(plain_key, encrypted_key, true);
 198 }
 199
 200 static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
 201 {
 202         struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
 203         int blen, ret;
 204         u8 *plain_blob_key;
 205
 206         blen = calc_blob_len(p->key_len);
 207         if (blen > MAX_BLOB_SIZE)
 208                 return -E2BIG;
 209
 210         plain_blob_key = kmalloc(AES_KEYSIZE_128, GFP_KERNEL);
 211         if (!plain_blob_key)
 212                 return -ENOMEM;
 213
 214         b->fmt_version = DCP_BLOB_VERSION;
 215         get_random_bytes(b->nonce, AES_KEYSIZE_128);
 216         get_random_bytes(plain_blob_key, AES_KEYSIZE_128);
 217
 218         ret = do_aead_crypto(p->key, b->payload, p->key_len, plain_blob_key,
 219                              b->nonce, true);
 220         if (ret) {
 221                 pr_err("Unable to encrypt blob payload: %i\n", ret);
 222                 goto out;
 223         }
 224
 225         ret = encrypt_blob_key(plain_blob_key, b->blob_key);
 226         if (ret) {
 227                 pr_err("Unable to encrypt blob key: %i\n", ret);
 228                 goto out;
 229         }
 230
 231         put_unaligned_le32(p->key_len, &b->payload_len);
 232         p->blob_len = blen;
 233         ret = 0;
 234
 235 out:
 236         memzero_explicit(plain_blob_key, AES_KEYSIZE_128);
 237         kfree(plain_blob_key);
 238
 239         return ret;
 240 }
 241
 242 static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
 243 {
 244         struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
 245         int blen, ret;
 246         u8 *plain_blob_key = NULL;
 247
 248         if (b->fmt_version != DCP_BLOB_VERSION) {
 249                 pr_err("DCP blob has bad version: %i, expected %i\n",
 250                        b->fmt_version, DCP_BLOB_VERSION);
 251                 ret = -EINVAL;
 252                 goto out;
 253         }
 254
 255         p->key_len = le32_to_cpu(b->payload_len);
 256         blen = calc_blob_len(p->key_len);
 257         if (blen != p->blob_len) {
 258                 pr_err("DCP blob has bad length: %i != %i\n", blen,
 259                        p->blob_len);
 260                 ret = -EINVAL;
 261                 goto out;
 262         }
 263
 264         plain_blob_key = kmalloc(AES_KEYSIZE_128, GFP_KERNEL);
 265         if (!plain_blob_key) {
 266                 ret = -ENOMEM;
 267                 goto out;
 268         }
 269
 270         ret = decrypt_blob_key(b->blob_key, plain_blob_key);
 271         if (ret) {
 272                 pr_err("Unable to decrypt blob key: %i\n", ret);
 273                 goto out;
 274         }
 275
 276         ret = do_aead_crypto(b->payload, p->key, p->key_len + DCP_BLOB_AUTHLEN,
 277                              plain_blob_key, b->nonce, false);
 278         if (ret) {
 279                 pr_err("Unwrap of DCP payload failed: %i\n", ret);
 280                 goto out;
 281         }
 282
 283         ret = 0;
 284 out:
 285         if (plain_blob_key) {
 286                 memzero_explicit(plain_blob_key, AES_KEYSIZE_128);
 287                 kfree(plain_blob_key);
 288         }
 289
 290         return ret;
 291 }
 292
 293 static int test_for_zero_key(void)
 294 {
 295         /*
 296          * Encrypting a plaintext of all 0x55 bytes will yield
 297          * this ciphertext in case the DCP test key is used.
 298          */
 299         static const u8 bad[] = {0x9a, 0xda, 0xe0, 0x54, 0xf6, 0x3d, 0xfa, 0xff,
 300                                  0x5e, 0xa1, 0x8e, 0x45, 0xed, 0xf6, 0xea, 0x6f};
 301         void *buf = NULL;
 302         int ret = 0;
 303
 304         if (skip_zk_test)
 305                 goto out;
 306
 307         buf = kmalloc(AES_BLOCK_SIZE, GFP_KERNEL);
 308         if (!buf) {
 309                 ret = -ENOMEM;
 310                 goto out;
 311         }
 312
 313         memset(buf, 0x55, AES_BLOCK_SIZE);
 314
 315         ret = do_dcp_crypto(buf, buf, true);
 316         if (ret)
 317                 goto out;
 318
 319         if (memcmp(buf, bad, AES_BLOCK_SIZE) == 0) {
 320                 pr_warn("Device neither in secure nor trusted mode!\n");
 321                 ret = -EINVAL;
 322         }
 323 out:
 324         kfree(buf);
 325         return ret;
 326 }
 327
 328 static int trusted_dcp_init(void)
 329 {
 330         int ret;
 331
 332         if (use_otp_key)
 333                 pr_info("Using DCP OTP key\n");
 334
 335         ret = test_for_zero_key();
 336         if (ret) {
 337                 pr_warn("Test for zero'ed keys failed: %i\n", ret);
 338
 339                 return -EINVAL;
 340         }
 341
 342         return register_key_type(&key_type_trusted);
 343 }
 344
 345 static void trusted_dcp_exit(void)
 346 {
 347         unregister_key_type(&key_type_trusted);
 348 }
 349
 350 struct trusted_key_ops dcp_trusted_key_ops = {
 351         .exit = trusted_dcp_exit,
 352         .init = trusted_dcp_init,
 353         .seal = trusted_dcp_seal,
 354         .unseal = trusted_dcp_unseal,
 355         .migratable = 0,
 356 };