[PATCH v13 14/20] appended signatures: Using db and dbx lists for signature verification

[Sudhakar Kuppusamy <sudhakar@linux.ibm.com>]

Signature verification: verify the kernel against lists of hashes that are
either in dbx or db list. If it is not in the dbx list then the trusted keys
from the db list are used to verify the signature.

Signed-off-by: Sudhakar Kuppusamy <sudhakar@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/commands/appendedsig/appendedsig.c | 94 +++++++++++++++++++-
 1 file changed, 93 insertions(+), 1 deletion(-)

diff --git a/grub-core/commands/appendedsig/appendedsig.c b/grub-core/commands/appendedsig/appendedsig.c
index bfa5f332e..b4b9e4cd3 100644
--- a/grub-core/commands/appendedsig/appendedsig.c
+++ b/grub-core/commands/appendedsig/appendedsig.c
@@ -521,6 +521,83 @@ extract_appended_signature (const grub_uint8_t *buf, grub_size_t bufsize,
   return grub_pkcs7_data_parse (signed_data, appendedsig_pkcs7_size, &sig->pkcs7);
 }
 
+static grub_err_t
+get_binary_hash (const grub_size_t binary_hash_size, const grub_uint8_t *data,
+                 const grub_size_t data_size, grub_uint8_t *hash, grub_size_t *hash_size)
+{
+  grub_packed_guid_t guid = { 0 };
+
+  /* support SHA256, SHA384 and SHA512 for binary hash */
+  if (binary_hash_size == SHA256_HASH_SIZE)
+    grub_memcpy (&guid, &GRUB_PKS_CERT_SHA256_GUID, GRUB_PACKED_GUID_SIZE);
+  else if (binary_hash_size == SHA384_HASH_SIZE)
+    grub_memcpy (&guid, &GRUB_PKS_CERT_SHA384_GUID, GRUB_PACKED_GUID_SIZE);
+  else if (binary_hash_size == SHA512_HASH_SIZE)
+    grub_memcpy (&guid, &GRUB_PKS_CERT_SHA512_GUID, GRUB_PACKED_GUID_SIZE);
+  else
+    {
+      grub_dprintf ("appendedsig", "unsupported hash type (%" PRIuGRUB_SIZE ") and "
+                    "skipped\n", binary_hash_size);
+      return GRUB_ERR_UNKNOWN_COMMAND;
+    }
+
+  return get_hash (&guid, data, data_size, hash, hash_size);
+}
+
+/*
+ * Verify binary hash against the db and dbx list.
+ * The following errors can occur:
+ *  - GRUB_ERR_BAD_SIGNATURE: indicates that the hash is in dbx list.
+ *  - GRUB_ERR_EOF: the hash could not be found in the db and dbx list.
+ *  - GRUB_ERR_NONE: the hash is found in db list.
+ */
+static grub_err_t
+verify_binary_hash (const grub_uint8_t *data, const grub_size_t data_size)
+{
+  grub_err_t rc = GRUB_ERR_NONE;
+  grub_uint32_t i;
+  grub_size_t hash_size = 0;
+  grub_uint8_t hash[GRUB_MAX_HASH_LEN] = { 0 };
+
+  for (i = 0; i < dbx.hash_entries; i++)
+    {
+      if (dbx.hashes[i] == NULL)
+        continue;
+
+      rc = get_binary_hash (dbx.hash_sizes[i], data, data_size, hash, &hash_size);
+      if (rc != GRUB_ERR_NONE)
+        continue;
+
+      if (hash_size == dbx.hash_sizes[i] &&
+          grub_memcmp (dbx.hashes[i], hash, hash_size) == 0)
+        {
+          grub_dprintf ("appendedsig", "the hash (%02x%02x%02x%02x) is present in the dbx list\n",
+                        hash[0], hash[1], hash[2], hash[3]);
+          return GRUB_ERR_BAD_SIGNATURE;
+        }
+    }
+
+  for (i = 0; i < db.hash_entries; i++)
+    {
+      if (db.hashes[i] == NULL)
+        continue;
+
+      rc = get_binary_hash (db.hash_sizes[i], data, data_size, hash, &hash_size);
+      if (rc != GRUB_ERR_NONE)
+        continue;
+
+      if (hash_size == db.hash_sizes[i] &&
+          grub_memcmp (db.hashes[i], hash, hash_size) == 0)
+        {
+          grub_dprintf ("appendedsig", "verified with a trusted hash (%02x%02x%02x%02x)\n",
+                        hash[0], hash[1], hash[2], hash[3]);
+          return GRUB_ERR_NONE;
+        }
+    }
+
+  return GRUB_ERR_EOF;
+}
+
 /*
  * Given a hash value 'hval', of hash specification 'hash', prepare the
  * S-expressions (sexp) and perform the signature verification.
@@ -565,7 +642,7 @@ grub_verify_appended_signature (const grub_uint8_t *buf, grub_size_t bufsize)
   grub_pkcs7_signer_t *si;
   grub_int32_t i;
 
-  if (!db.cert_entries)
+  if (!db.cert_entries && !db.hash_entries)
     return grub_error (GRUB_ERR_BAD_SIGNATURE, "no trusted keys to verify against");
 
   err = extract_appended_signature (buf, bufsize, &sig);
@@ -574,6 +651,21 @@ grub_verify_appended_signature (const grub_uint8_t *buf, grub_size_t bufsize)
 
   datasize = bufsize - sig.signature_len;
 
+  /*
+   * If signature verification is enabled with dynamic key management mode,
+   * Verify binary hash against the db and dbx list.
+   */
+  if (append_key_mgmt == true)
+    {
+      err = verify_binary_hash (buf, datasize);
+      if (err == GRUB_ERR_BAD_SIGNATURE)
+        {
+          grub_pkcs7_data_release (&sig.pkcs7);
+          return grub_error (err,
+                             "failed to verify the binary hash against a trusted binary hash");
+        }
+    }
+
   /* Verify signature using trusted keys from db list. */
   for (i = 0; i < sig.pkcs7.signer_count; i++)
     {
-- 
2.50.1 (Apple Git-155)


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