tpm2-util: auto-detect supported PCR banks

Previously, we'd encode PCR policies strictly with the SHA256 PCR bank
set. However, as it appears not all hw implement those. Sad.

Let's add some minimal logic to auto-detect supported PCR banks: if
SHA256 is supported, use that. But if not, automatically fall back to
SHA1.

This then changes both the LUKS code, and the credentials code to
serialize the selected bank, along with the rest of the data in order to
make this robust.

This extends the LUK2 JSON metadata in a compatible way. The credentials
encryption format is modified in an incompatible way however, but given
that this is not part of any official release should be OK.

Fixes: #20134

1 files changed, 22 insertions, 1 deletions

diff --git a/src/cryptsetup/cryptsetup-tpm2.c b/src/cryptsetup/cryptsetup-tpm2.c
index 4757c5882d..8da1880a35 100644
--- a/src/cryptsetup/cryptsetup-tpm2.c
+++ b/src/cryptsetup/cryptsetup-tpm2.c
@@ -13,6 +13,7 @@ int acquire_tpm2_key(
                 const char *volume_name,
                 const char *device,
                 uint32_t pcr_mask,
+                uint16_t pcr_bank,
                 const char *key_file,
                 size_t key_file_size,
                 uint64_t key_file_offset,
@@ -62,7 +63,7 @@ int acquire_tpm2_key(
                 blob = loaded_blob;
         }
 
-        return tpm2_unseal(device, pcr_mask, blob, blob_size, policy_hash, policy_hash_size, ret_decrypted_key, ret_decrypted_key_size);
+        return tpm2_unseal(device, pcr_mask, pcr_bank, blob, blob_size, policy_hash, policy_hash_size, ret_decrypted_key, ret_decrypted_key_size);
 }
 
 int find_tpm2_auto_data(
@@ -70,6 +71,7 @@ int find_tpm2_auto_data(
                 uint32_t search_pcr_mask,
                 int start_token,
                 uint32_t *ret_pcr_mask,
+                uint16_t *ret_pcr_bank,
                 void **ret_blob,
                 size_t *ret_blob_size,
                 void **ret_policy_hash,
@@ -81,6 +83,7 @@ int find_tpm2_auto_data(
         size_t blob_size = 0, policy_hash_size = 0;
         int r, keyslot = -1, token = -1;
         uint32_t pcr_mask = 0;
+        uint16_t pcr_bank = UINT16_MAX; /* default: pick automatically */
 
         assert(cd);
 
@@ -119,6 +122,23 @@ int find_tpm2_auto_data(
                     search_pcr_mask != pcr_mask) /* PCR mask doesn't match what is configured, ignore this entry */
                         continue;
 
+                /* The bank field is optional, since it was added in systemd 250 only. Before the bank was hardcoded to SHA256 */
+                assert(pcr_bank == UINT16_MAX);
+                w = json_variant_by_key(v, "tpm2-pcr-bank");
+                if (w) {
+                        /* The PCR bank field is optional */
+
+                        if (!json_variant_is_string(w))
+                                return log_error_errno(SYNTHETIC_ERRNO(EINVAL),
+                                                       "TPM2 PCR bank is not a string.");
+
+                        r = tpm2_pcr_bank_from_string(json_variant_string(w));
+                        if (r < 0)
+                                return log_error_errno(r, "TPM2 PCR bank invalid or not supported: %s", json_variant_string(w));
+
+                        pcr_bank = r;
+                }
+
                 assert(!blob);
                 w = json_variant_by_key(v, "tpm2-blob");
                 if (!w || !json_variant_is_string(w))
@@ -163,6 +183,7 @@ int find_tpm2_auto_data(
         *ret_policy_hash_size = policy_hash_size;
         *ret_keyslot = keyslot;
         *ret_token = token;
+        *ret_pcr_bank = pcr_bank;
 
         return 0;
 }