To verify the kernel's signature: verify the kernel binary against lists of
binary hashes
that are either distrusted or trusted. If it is not list in either trusted or
distrusted hashes list
then the trusted keys from the trusted key list are used to verify the
signature.
Signed-off-by: Sudhakar Kuppusamy <sudha...@linux.ibm.com>
Reviewed-by: Stefan Berger <stef...@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avn...@linux.ibm.com>
---
grub-core/commands/appendedsig/appendedsig.c | 199 +++++++++++++------
1 file changed, 142 insertions(+), 57 deletions(-)
diff --git a/grub-core/commands/appendedsig/appendedsig.c
b/grub-core/commands/appendedsig/appendedsig.c
index b24112050..3abb45ae0 100644
--- a/grub-core/commands/appendedsig/appendedsig.c
+++ b/grub-core/commands/appendedsig/appendedsig.c
@@ -454,6 +454,83 @@ extract_appended_signature (const grub_uint8_t *buf,
grub_size_t bufsize,
return parse_pkcs7_signedData (appsigdata, 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_uuid_t guid = { 0 };
+
+ /* support SHA256, SHA384 and SHA512 for binary hash */
+ if (binary_hash_size == 32)
+ grub_memcpy (&guid, &GRUB_PKS_CERT_SHA256_GUID, GRUB_UUID_SIZE);
+ else if (binary_hash_size == 48)
+ grub_memcpy (&guid, &GRUB_PKS_CERT_SHA384_GUID, GRUB_UUID_SIZE);
+ else if (binary_hash_size == 64)
+ grub_memcpy (&guid, &GRUB_PKS_CERT_SHA512_GUID, GRUB_UUID_SIZE);
+ else
+ {
+ grub_dprintf ("appendedsig", "unsupported hash type (%" PRIuGRUB_SIZE ")
and skipping binary hash\n",
+ binary_hash_size);
+ return GRUB_ERR_UNKNOWN_COMMAND;
+ }
+
+ return get_hash (&guid, data, data_size, hash, hash_size);
+}
+
+/*
+ * Verify binary hash against the list of binary hashes that are distrusted
+ * and trusted.
+ * The following errors can occur:
+ * - GRUB_ERR_BAD_SIGNATURE: indicates that the hash is distrusted.
+ * - GRUB_ERR_NONE: the hash is trusted, since it was found in the trusted
hashes list
+ * - GRUB_ERR_EOF: the hash could not be found in the hashes 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_size_t i = 0, hash_size = 0;
+ grub_uint8_t hash[GRUB_MAX_HASH_SIZE] = { 0 };
+
+ for (i = 0; i < dbx.signature_entries; i++)
+ {
+ rc = get_binary_hash (dbx.signature_size[i], data, data_size, hash,
&hash_size);
+ if (rc != GRUB_ERR_NONE)
+ continue;
+
+ if (hash_size == dbx.signature_size[i] &&
+ grub_memcmp (dbx.signatures[i], hash, hash_size) == 0)
+ {
+ grub_dprintf ("appendedsig", "the binary hash (%02x%02x%02x%02x) was
listed as distrusted\n",
+ hash[0], hash[1], hash[2], hash[3]);
+ return GRUB_ERR_BAD_SIGNATURE;
+ }
+ }
+
+ for (i = 0; i < db.signature_entries; i++)
+ {
+ rc = get_binary_hash (db.signature_size[i], data, data_size, hash,
&hash_size);
+ if (rc != GRUB_ERR_NONE)
+ continue;
+
+ if (hash_size == db.signature_size[i] &&
+ grub_memcmp (db.signatures[i], hash, hash_size) == 0)
+ {
+ grub_dprintf ("appendedsig", "verified with a trusted binary hash
(%02x%02x%02x%02x)\n",
+ hash[0], hash[1], hash[2], hash[3]);
+ return GRUB_ERR_NONE;
+ }
+ }
+
+ return GRUB_ERR_EOF;
+}
+
+
+/*
+ * Verify the kernel's integrity, the trusted key will be used from
+ * the trusted key list. If it fails, verify it against the list of binary
hashes
+ * that are distrusted and trusted.
+ */
static grub_err_t
grub_verify_appended_signature (const grub_uint8_t *buf, grub_size_t bufsize)
{
@@ -463,12 +540,12 @@ grub_verify_appended_signature (const grub_uint8_t *buf,
grub_size_t bufsize)
unsigned char *hash;
gcry_mpi_t hashmpi;
gcry_err_code_t rc;
- struct x509_certificate *pk;
+ struct x509_certificate *cert;
struct grub_appended_signature sig;
struct pkcs7_signerInfo *si;
int i;
- if (!db.key_entries)
+ if (!db.key_entries && !db.signature_entries)
return grub_error (GRUB_ERR_BAD_SIGNATURE, N_("No trusted keys to verify
against"));
err = extract_appended_signature (buf, bufsize, &sig);
@@ -476,69 +553,77 @@ grub_verify_appended_signature (const grub_uint8_t *buf,
grub_size_t bufsize)
return err;
datasize = bufsize - sig.signature_len;
-
- for (i = 0; i < sig.pkcs7.signerInfo_count; i++)
+ err = verify_binary_hash (buf, datasize);
+ if (err != GRUB_ERR_EOF && err != GRUB_ERR_NONE)
{
- /*
- * This could be optimised in a couple of ways:
- * - we could only compute hashes once per hash type
- * - we could track signer information and only verify where IDs match
- * For now we do the naive O(trusted keys * pkcs7 signers) approach.
- */
- si = &sig.pkcs7.signerInfos[i];
- context = grub_zalloc (si->hash->contextsize);
- if (!context)
- return grub_errno;
-
- si->hash->init (context);
- si->hash->write (context, buf, datasize);
- si->hash->final (context);
- hash = si->hash->read (context);
-
- grub_dprintf ("appendedsig", "data size %" PRIxGRUB_SIZE ", signer %d
hash %02x%02x%02x%02x...\n",
- datasize, i, hash[0], hash[1], hash[2], hash[3]);
-
- err = GRUB_ERR_BAD_SIGNATURE;
- for (pk = db.keys; pk; pk = pk->next)
+ err = grub_error (err, N_("failed to verify binary-hash/signature with
any trusted binary-hash/key\n"));
+ pkcs7_signedData_release (&sig.pkcs7);
+ return err;
+ }
+ else if (err == GRUB_ERR_EOF)
+ {
+ /* Binary hash was not found in trusted and distrusted list: check
signature now */
+ for (i = 0; i < sig.pkcs7.signerInfo_count; i++)
{
- rc = grub_crypto_rsa_pad (&hashmpi, hash, si->hash, pk->mpis[0]);
- if (rc)
- {
- err = grub_error (GRUB_ERR_BAD_SIGNATURE,
- N_("Error padding hash for RSA verification:
%d"), rc);
- grub_free (context);
- goto cleanup;
- }
-
- rc = _gcry_pubkey_spec_rsa.verify (0, hashmpi, &si->sig_mpi,
pk->mpis, NULL, NULL);
- gcry_mpi_release (hashmpi);
-
- if (rc == 0)
+ /*
+ * This could be optimised in a couple of ways:
+ * - we could only compute hashes once per hash type
+ * - we could track signer information and only verify where IDs
match
+ * For now we do the naive O(db.keys * pkcs7 signers) approach.
+ */
+ si = &sig.pkcs7.signerInfos[i];
+ context = grub_zalloc (si->hash->contextsize);
+ if (context == NULL)
+ return grub_errno;
+
+ si->hash->init (context);
+ si->hash->write (context, buf, datasize);
+ si->hash->final (context);
+ hash = si->hash->read (context);
+
+ grub_dprintf ("appendedsig",
+ "data size %" PRIxGRUB_SIZE ", signer %d hash
%02x%02x%02x%02x...\n",
+ datasize, i, hash[0], hash[1], hash[2], hash[3]);
+
+ err = GRUB_ERR_BAD_SIGNATURE;
+ for (cert = db.keys; cert; cert = cert->next)
{
- grub_dprintf ("appendedsig", "verify signer %d with key '%s'
succeeded\n",
- i, pk->subject);
- err = GRUB_ERR_NONE;
- break;
+ rc = grub_crypto_rsa_pad (&hashmpi, hash, si->hash,
cert->mpis[0]);
+ if (rc != 0)
+ {
+ err = grub_error (GRUB_ERR_BAD_SIGNATURE,
+ N_("Error padding hash for RSA
verification: %d"), rc);
+ grub_free (context);
+ pkcs7_signedData_release (&sig.pkcs7);
+ return err;
+ }
+
+ rc = _gcry_pubkey_spec_rsa.verify (0, hashmpi, &si->sig_mpi,
cert->mpis, NULL, NULL);
+ gcry_mpi_release (hashmpi);
+ if (rc == 0)
+ {
+ grub_dprintf ("appendedsig", "verify signer %d with key '%s'
succeeded\n",
+ i, cert->subject);
+ err = GRUB_ERR_NONE;
+ break;
+ }
+
+ grub_dprintf ("appendedsig", "verify signer %d with key '%s'
failed with %d\n",
+ i, cert->subject, rc);
}
-
- grub_dprintf ("appendedsig", "verify signer %d with key '%s' failed
with %d\n",
- i, pk->subject, rc);
- }
-
- grub_free (context);
-
- if (err == GRUB_ERR_NONE)
- break;
+ grub_free (context);
+ if (err == GRUB_ERR_NONE)
+ break;
+ }
}
- /* If we didn't verify, provide a neat message */
- if (err != GRUB_ERR_NONE)
- err = grub_error (GRUB_ERR_BAD_SIGNATURE,
- N_("Failed to verify signature against a trusted key"));
-
-cleanup:
pkcs7_signedData_release (&sig.pkcs7);
+ if (err != GRUB_ERR_NONE)
+ err = grub_error (err, N_("failed to verify signature with any trusted
key\n"));
+ else
+ grub_dprintf ("appendedsig", "successfully verified the signature with a
trusted key\n");
+
return err;
}
--
2.43.5
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