src/cryptenroll/cryptenroll-tpm2.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include "alloc-util.h"
   4 #include "cryptenroll-tpm2.h"
   5 #include "hexdecoct.h"
   6 #include "json.h"
   7 #include "memory-util.h"
   8 #include "tpm2-util.h"
   9
  10 static int search_policy_hash(
  11                 struct crypt_device *cd,
  12                 const void *hash,
  13                 size_t hash_size) {
  14
  15         int r;
  16
  17         assert(cd);
  18         assert(hash || hash_size == 0);
  19
  20         if (hash_size == 0)
  21                 return 0;
  22
  23         for (int token = 0; token < sym_crypt_token_max(CRYPT_LUKS2); token ++) {
  24                 _cleanup_(json_variant_unrefp) JsonVariant *v = NULL;
  25                 _cleanup_free_ void *thash = NULL;
  26                 size_t thash_size = 0;
  27                 int keyslot;
  28                 JsonVariant *w;
  29
  30                 r = cryptsetup_get_token_as_json(cd, token, "systemd-tpm2", &v);
  31                 if (IN_SET(r, -ENOENT, -EINVAL, -EMEDIUMTYPE))
  32                         continue;
  33                 if (r < 0)
  34                         return log_error_errno(r, "Failed to read JSON token data off disk: %m");
  35
  36                 keyslot = cryptsetup_get_keyslot_from_token(v);
  37                 if (keyslot < 0)
  38                         return log_error_errno(keyslot, "Failed to determine keyslot of JSON token: %m");
  39
  40                 w = json_variant_by_key(v, "tpm2-policy-hash");
  41                 if (!w || !json_variant_is_string(w))
  42                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
  43                                                "TPM2 token data lacks 'tpm2-policy-hash' field.");
  44
  45                 r = unhexmem(json_variant_string(w), (size_t) -1, &thash, &thash_size);
  46                 if (r < 0)
  47                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
  48                                                "Invalid base64 data in 'tpm2-policy-hash' field.");
  49
  50                 if (memcmp_nn(hash, hash_size, thash, thash_size) == 0)
  51                         return keyslot; /* Found entry with same hash. */
  52         }
  53
  54         return -ENOENT; /* Not found */
  55 }
  56
  57 int enroll_tpm2(struct crypt_device *cd,
  58                 const void *volume_key,
  59                 size_t volume_key_size,
  60                 const char *device,
  61                 uint32_t pcr_mask) {
  62
  63         _cleanup_(erase_and_freep) void *secret = NULL, *secret2 = NULL;
  64         _cleanup_(json_variant_unrefp) JsonVariant *v = NULL;
  65         _cleanup_(erase_and_freep) char *base64_encoded = NULL;
  66         size_t secret_size, secret2_size, blob_size, hash_size;
  67         _cleanup_free_ void *blob = NULL, *hash = NULL;
  68         const char *node;
  69         int r, keyslot;
  70
  71         assert(cd);
  72         assert(volume_key);
  73         assert(volume_key_size > 0);
  74         assert(pcr_mask < (1U << TPM2_PCRS_MAX)); /* Support 24 PCR banks */
  75
  76         assert_se(node = crypt_get_device_name(cd));
  77
  78         r = tpm2_seal(device, pcr_mask, &secret, &secret_size, &blob, &blob_size, &hash, &hash_size);
  79         if (r < 0)
  80                 return r;
  81
  82         /* Let's see if we already have this specific PCR policy hash enrolled, if so, exit early. */
  83         r = search_policy_hash(cd, hash, hash_size);
  84         if (r == -ENOENT)
  85                 log_debug_errno(r, "PCR policy hash not yet enrolled, enrolling now.");
  86         else if (r < 0)
  87                 return r;
  88         else {
  89                 log_info("This PCR set is already enrolled, executing no operation.");
  90                 return r; /* return existing keyslot, so that wiping won't kill it */
  91         }
  92
  93         /* Quick verification that everything is in order, we are not in a hurry after all. */
  94         log_debug("Unsealing for verification...");
  95         r = tpm2_unseal(device, pcr_mask, blob, blob_size, hash, hash_size, &secret2, &secret2_size);
  96         if (r < 0)
  97                 return r;
  98
  99         if (memcmp_nn(secret, secret_size, secret2, secret2_size) != 0)
 100                 return log_error_errno(SYNTHETIC_ERRNO(ENOTRECOVERABLE), "TPM2 seal/unseal verification failed.");
 101
 102         /* let's base64 encode the key to use, for compat with homed (and it's easier to every type it in by keyboard, if that might end up being necessary. */
 103         r = base64mem(secret, secret_size, &base64_encoded);
 104         if (r < 0)
 105                 return log_error_errno(r, "Failed to base64 encode secret key: %m");
 106
 107         r = cryptsetup_set_minimal_pbkdf(cd);
 108         if (r < 0)
 109                 return log_error_errno(r, "Failed to set minimal PBKDF: %m");
 110
 111         keyslot = crypt_keyslot_add_by_volume_key(
 112                         cd,
 113                         CRYPT_ANY_SLOT,
 114                         volume_key,
 115                         volume_key_size,
 116                         base64_encoded,
 117                         strlen(base64_encoded));
 118         if (keyslot < 0)
 119                 return log_error_errno(keyslot, "Failed to add new TPM2 key to %s: %m", node);
 120
 121         r = tpm2_make_luks2_json(keyslot, pcr_mask, blob, blob_size, hash, hash_size, &v);
 122         if (r < 0)
 123                 return log_error_errno(r, "Failed to prepare TPM2 JSON token object: %m");
 124
 125         r = cryptsetup_add_token_json(cd, v);
 126         if (r < 0)
 127                 return log_error_errno(r, "Failed to add TPM2 JSON token to LUKS2 header: %m");
 128
 129         log_info("New TPM2 token enrolled as key slot %i.", keyslot);
 130         return keyslot;
 131 }