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grub2/0471-appendedsig-While-verifying-the-kernel-use-trusted-a.patch
Nicolas Frayer 4b6a3a3027 ieee1275: Appended signature support 
Resolves: #RHEL-24742
Signed-off-by: Nicolas Frayer <nfrayer@redhat.com>
2025-05-22 01:30:39 +02:00

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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Sudhakar Kuppusamy <sudhakar@linux.ibm.com>
Date: Thu, 27 Mar 2025 01:02:38 +0530
Subject: [PATCH] appendedsig: While verifying the kernel, use trusted and
distrusted lists
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 <sudhakar@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
---
grub-core/commands/appendedsig/appendedsig.c | 193 +++++++++++++++++++--------
1 file changed, 139 insertions(+), 54 deletions(-)
diff --git a/grub-core/commands/appendedsig/appendedsig.c b/grub-core/commands/appendedsig/appendedsig.c
index 994852f..07d6b39 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;
- }
+ /*
+ * 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;
- rc = _gcry_pubkey_spec_rsa.verify (0, hashmpi, &si->sig_mpi, pk->mpis, NULL, NULL);
- gcry_mpi_release (hashmpi);
+ si->hash->init (context);
+ si->hash->write (context, buf, datasize);
+ si->hash->final (context);
+ hash = si->hash->read (context);
- if (rc == 0)
- {
- grub_dprintf ("appendedsig", "verify signer %d with key '%s' succeeded\n",
- i, pk->subject);
- err = GRUB_ERR_NONE;
- break;
- }
+ 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]);
- grub_dprintf ("appendedsig", "verify signer %d with key '%s' failed with %d\n",
- i, pk->subject, rc);
- }
+ err = GRUB_ERR_BAD_SIGNATURE;
+ for (cert = db.keys; cert; cert = cert->next)
+ {
+ 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;
+ }
- grub_free (context);
+ 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;
+ }
- if (err == GRUB_ERR_NONE)
- break;
+ grub_dprintf ("appendedsig", "verify signer %d with key '%s' failed with %d\n",
+ i, cert->subject, rc);
+ }
+ 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;
}
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