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appended signatures: GRUB commands to manage the hashes

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Introducing the following GRUB commands to manage certificate/binary
hashes.

  1. append_list_dbx:
      Show the list of distrusted certificates and binary/certificate
      hashes from the dbx list.
  2. append_add_db_hash:
      Add the trusted binary hash to the db list.
  3. append_add_dbx_hash:
      Add the distrusted certificate/binary hash to the dbx list.

Note that if signature verification (check_appended_signatures) is set to yes,
the append_add_db_hash and append_add_dbx_hash commands only accept the file
‘hash_file’ that is signed with an appended signature.

Signed-off-by: Sudhakar Kuppusamy <sudhakar@linux.ibm.com>
Tested-by: Sridhar Markonda <sridharm@linux.ibm.com>
Reviewed-by: Avnish Chouhan <avnish@linux.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Sudhakar Kuppusamy 2025-10-06 12:55:01 +05:30 committed by Daniel Kiper
parent 6cb58b1c9e
commit 7f68c71952
2 changed files with 281 additions and 0 deletions
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279
grub-core/commands/appendedsig/appendedsig.c
View File

@ -52,6 +52,9 @@ GRUB_MOD_LICENSE ("GPLv3+");
#define SHA384_HASH_SIZE 48
#define SHA512_HASH_SIZE 64
#define OPTION_BINARY_HASH 0
#define OPTION_CERT_HASH 1
/*
* This structure is extracted from scripts/sign-file.c in the linux kernel
* source. It was licensed as LGPLv2.1+, which is GPLv3+ compatible.
@ -126,6 +129,13 @@ static grub_pks_t *pks_keystore;
/* Appended signature size. */
static grub_size_t append_sig_len = 0;
static const struct grub_arg_option options[] =
{
{"binary-hash", 'b', 0, N_("hash file of the binary."), 0, ARG_TYPE_PATHNAME},
{"cert-hash", 'c', 1, N_("hash file of the certificate."), 0, ARG_TYPE_PATHNAME},
{0, 0, 0, 0, 0, 0}
};
static grub_ssize_t
pseudo_read (struct grub_file *file, char *buf, grub_size_t len)
{
@ -546,6 +556,69 @@ remove_cert_from_db (const grub_uint8_t *data, const grub_size_t data_size)
return rc;
}
static bool
cert_fingerprint_match (const grub_uint8_t *hash_data, const grub_size_t hash_data_size,
const grub_x509_cert_t *cert)
{
grub_int32_t type;
if (hash_data_size == SHA256_HASH_SIZE)
type = GRUB_FINGERPRINT_SHA256;
else if (hash_data_size == SHA384_HASH_SIZE)
type = GRUB_FINGERPRINT_SHA384;
else if (hash_data_size == SHA512_HASH_SIZE)
type = GRUB_FINGERPRINT_SHA512;
else
{
grub_dprintf ("appendedsig", "unsupported fingerprint hash type "
"(%" PRIuGRUB_SIZE ") \n", hash_data_size);
return false;
}
if (grub_memcmp (cert->fingerprint[type], hash_data, hash_data_size) == 0)
return true;
return false;
}
static void
remove_hash_from_db (const grub_uint8_t *hash_data, const grub_size_t hash_data_size,
const bool bin_hash)
{
grub_uint32_t i;
grub_x509_cert_t *cert;
if (bin_hash == true)
{
for (i = 0; i < db.hash_entries; i++)
{
if (db.hashes[i] == NULL)
continue;
if (grub_memcmp (db.hashes[i], hash_data, hash_data_size) == 0)
{
grub_dprintf ("appendedsig", "removed distrusted hash %02x%02x%02x%02x.. from the db list\n",
db.hashes[i][0], db.hashes[i][1], db.hashes[i][2], db.hashes[i][3]);
grub_free (db.hashes[i]);
db.hashes[i] = NULL;
db.hash_sizes[i] = 0;
break;
}
}
}
else
{
for (cert = db.certs; cert != NULL; cert = cert->next)
{
if (cert_fingerprint_match (hash_data, hash_data_size, cert) == true)
{
_remove_cert_from_db (cert);
break;
}
}
}
}
static grub_err_t
file_read_whole (grub_file_t file, grub_uint8_t **buf, grub_size_t *len)
{
@ -1010,6 +1083,192 @@ grub_cmd_list_db (grub_command_t cmd __attribute__ ((unused)), int argc __attrib
return GRUB_ERR_NONE;
}
static grub_err_t
grub_cmd_list_dbx (grub_command_t cmd __attribute__((unused)),
int argc __attribute__((unused)), char **args __attribute__((unused)))
{
struct x509_certificate *cert;
grub_uint32_t i, cert_num = 1;
if (append_key_mgmt == false)
return grub_error (GRUB_ERR_ACCESS_DENIED,
"append_list_dbx command is unsupported in static key mode");
for (cert = dbx.certs; cert != NULL; cert = cert->next, cert_num++)
print_certificate (cert, cert_num);
for (i = 0; i < dbx.hash_entries; i++)
{
if (dbx.hashes[i] != NULL)
{
grub_printf ("\nCertificate/Binary hash: %u\n", i + 1);
grub_printf (" Hash: sha%" PRIuGRUB_SIZE "\n ", dbx.hash_sizes[i] * 8);
hexdump_colon (dbx.hashes[i], dbx.hash_sizes[i]);
}
}
return GRUB_ERR_NONE;
}
/*
* Remove the trusted binary hash from the dbx list if present. And add them to
* the db list if it is not already present.
*
* Note: When signature verification is enabled, this command only accepts the
* binary hash file that is signed with an appended signature. The signature is
* verified by the appendedsig module. If verification succeeds, the binary hash
* is added to the db list. Otherwise, an error is posted and the binary hash is
* not added.
* When signature verification is disabled, it accepts the binary hash file
* without an appended signature and adds it to the db list.
*
* Also, note that the adding of the trusted binary hash using this command does
* not persist across reboots.
*/
static grub_err_t
grub_cmd_add_db_hash (grub_command_t cmd __attribute__((unused)), int argc, char**args)
{
grub_err_t rc;
grub_file_t hash_file;
grub_uint8_t *hash_data = NULL;
grub_size_t hash_data_size = 0;
if (append_key_mgmt == false)
return grub_error (GRUB_ERR_ACCESS_DENIED,
"append_add_db_hash command is unsupported in static key mode");
if (argc != 1)
return grub_error (GRUB_ERR_BAD_ARGUMENT,
"a trusted binary hash file is expected in binary format\n"
"Example:\n\tappend_add_db_hash <BINARY HASH FILE>\n");
if (!grub_strlen (args[0]))
return grub_error (GRUB_ERR_BAD_FILENAME, "missing trusted binary hash file");
hash_file = grub_file_open (args[0], GRUB_FILE_TYPE_HASH_TRUST | GRUB_FILE_TYPE_NO_DECOMPRESS);
if (hash_file == NULL)
return grub_error (GRUB_ERR_FILE_NOT_FOUND, "unable to open %s file", args[0]);
rc = file_read_whole (hash_file, &hash_data, &hash_data_size);
grub_file_close (hash_file);
if (rc != GRUB_ERR_NONE)
return rc;
/*
* If signature verification is enabled (check_sigs is set to true), obtain
* the actual hash data size by subtracting the appended signature size from
* the hash data size because the hash has an appended signature, and this
* actual hash data size is used to get the hash data.
*/
if (check_sigs == true)
hash_data_size -= append_sig_len;
grub_dprintf ("appendedsig",
"adding a trusted binary hash %02x%02x%02x%02x... with size of %" PRIuGRUB_SIZE "\n",
hash_data[0], hash_data[1], hash_data[2], hash_data[3], hash_data_size);
/* Only accept SHA256, SHA384 and SHA512 binary hash */
if (hash_data_size != SHA256_HASH_SIZE && hash_data_size != SHA384_HASH_SIZE &&
hash_data_size != SHA512_HASH_SIZE)
{
grub_free (hash_data);
return grub_error (GRUB_ERR_BAD_SIGNATURE, "unacceptable trusted binary hash type");
}
rc = add_hash (hash_data, hash_data_size, &db);
grub_free (hash_data);
return rc;
}
/*
* Remove the distrusted binary/certificate hash from the db list if present.
* And add them to the dbx list if it is not already present.
*
* Note: When signature verification is enabled, this command only accepts the
* binary/certificate hash file that is signed with an appended signature. The
* signature is verified by the appendedsig module. If verification succeeds,
* the binary/certificate hash is added to the dbx list. Otherwise, an error is
* posted and the binary/certificate hash is not added.
* When signature verification is disabled, it accepts the binary/certificate
* hash file without an appended signature and adds it to the dbx list.
*
* Also, note that the adding of the distrusted binary/certificate hash using
* this command does not persist across reboots.
*/
static grub_err_t
grub_cmd_add_dbx_hash (grub_extcmd_context_t ctxt, int argc __attribute__ ((unused)),
char **args __attribute__ ((unused)))
{
grub_err_t rc;
grub_file_t hash_file;
grub_uint8_t *hash_data = NULL;
grub_size_t hash_data_size = 0;
char *file_path;
if (append_key_mgmt == false)
return grub_error (GRUB_ERR_ACCESS_DENIED,
"append_add_dbx_hash command is unsupported in static key mode");
if (!ctxt->state[OPTION_BINARY_HASH].set && !ctxt->state[OPTION_CERT_HASH].set)
return grub_error (GRUB_ERR_BAD_ARGUMENT,
"a distrusted certificate/binary hash file is expected in binary format\n"
"Example:\n\tappend_add_dbx_hash [option] <FILE>\n"
"option:\n[-b|--binary-hash] FILE [BINARY HASH FILE]\n"
"[-c|--cert-hash] FILE [CERTFICATE HASH FILE]\n");
if (ctxt->state[OPTION_BINARY_HASH].arg == NULL && ctxt->state[OPTION_CERT_HASH].arg == NULL)
return grub_error (GRUB_ERR_BAD_FILENAME, "missing distrusted certificate/binary hash file");
if (ctxt->state[OPTION_BINARY_HASH].arg != NULL)
file_path = ctxt->state[OPTION_BINARY_HASH].arg;
else
file_path = ctxt->state[OPTION_CERT_HASH].arg;
hash_file = grub_file_open (file_path, GRUB_FILE_TYPE_HASH_TRUST | GRUB_FILE_TYPE_NO_DECOMPRESS);
if (hash_file == NULL)
return grub_error (GRUB_ERR_FILE_NOT_FOUND, "unable to open %s file", file_path);
rc = file_read_whole (hash_file, &hash_data, &hash_data_size);
grub_file_close (hash_file);
if (rc != GRUB_ERR_NONE)
return rc;
/*
* If signature verification is enabled (check_sigs is set to true), obtain
* the actual hash data size by subtracting the appended signature size from
* the hash data size because the hash has an appended signature, and this
* actual hash data size is used to get the hash data.
*/
if (check_sigs == true)
hash_data_size -= append_sig_len;
grub_dprintf ("appendedsig",
"adding a distrusted certificate/binary hash %02x%02x%02x%02x..."
" with size of %" PRIuGRUB_SIZE "\n", hash_data[0], hash_data[1],
hash_data[2], hash_data[3], hash_data_size);
if (ctxt->state[OPTION_BINARY_HASH].set || ctxt->state[OPTION_CERT_HASH].set)
{
/* Only accept SHA256, SHA384 and SHA512 certificate/binary hash */
if (hash_data_size != SHA256_HASH_SIZE && hash_data_size != SHA384_HASH_SIZE &&
hash_data_size != SHA512_HASH_SIZE)
{
grub_free (hash_data);
return grub_error (GRUB_ERR_BAD_SIGNATURE,
"unacceptable distrusted certificate/binary hash type");
}
}
/* Remove distrusted binary hash/certificate from the db list if present. */
remove_hash_from_db (hash_data, hash_data_size,
(ctxt->state[OPTION_BINARY_HASH].set) ? true : false);
rc = add_hash (hash_data, hash_data_size, &dbx);
grub_free (hash_data);
return rc;
}
/* Add the X.509 certificates/binary hash to the db list from PKS. */
static grub_err_t
load_pks2db (void)
@ -1292,6 +1551,11 @@ appendedsig_init (grub_file_t io __attribute__ ((unused)), enum grub_file_type t
* verifier, but we lack the hubris required to take this on. Instead,
* require that it have an appended signature.
*/
case GRUB_FILE_TYPE_HASH_TRUST:
/*
* This is a certificate/binary hash to add to db/dbx. This needs to be
* verified or blocked.
*/
case GRUB_FILE_TYPE_LINUX_KERNEL:
case GRUB_FILE_TYPE_GRUB_MODULE:
/*
@ -1333,6 +1597,8 @@ struct grub_file_verifier grub_appendedsig_verifier = {
};
static grub_command_t cmd_verify, cmd_list_db, cmd_dbx_cert, cmd_db_cert;
static grub_command_t cmd_list_dbx, cmd_db_hash;
static grub_extcmd_t cmd_dbx_hash;
GRUB_MOD_INIT (appendedsig)
{
@ -1412,6 +1678,16 @@ GRUB_MOD_INIT (appendedsig)
cmd_dbx_cert = grub_register_command ("append_add_dbx_cert", grub_cmd_dbx_cert, N_("<X509_CERTIFICATE>"),
N_("Add distrusted X509_CERTIFICATE to the dbx list"));
cmd_list_dbx = grub_register_command ("append_list_dbx", grub_cmd_list_dbx, 0,
N_("Show the list of distrusted certificates and"
" certificate/binary hashes from the dbx list"));
cmd_db_hash = grub_register_command ("append_add_db_hash", grub_cmd_add_db_hash, N_("BINARY HASH FILE"),
N_("Add trusted BINARY HASH to the db list."));
cmd_dbx_hash = grub_register_extcmd ("append_add_dbx_hash", grub_cmd_add_dbx_hash, 0,
N_("[-b|--binary-hash] FILE [BINARY HASH FILE]\n"
"[-c|--cert-hash] FILE [CERTFICATE HASH FILE]"),
N_("Add distrusted CERTFICATE/BINARY HASH to the dbx list."), options);
grub_verifier_register (&grub_appendedsig_verifier);
grub_dl_set_persistent (mod);
}
@ -1434,4 +1710,7 @@ GRUB_MOD_FINI (appendedsig)
grub_unregister_command (cmd_list_db);
grub_unregister_command (cmd_db_cert);
grub_unregister_command (cmd_dbx_cert);
grub_unregister_command (cmd_list_dbx);
grub_unregister_command (cmd_db_hash);
grub_unregister_extcmd (cmd_dbx_hash);
}

2
include/grub/file.h
View File

@ -115,6 +115,8 @@ enum grub_file_type
GRUB_FILE_TYPE_HASHLIST,
/* File hashed by hashsum. */
GRUB_FILE_TYPE_TO_HASH,
/* File holding certificiate/binary hash to add to db/dbx. */
GRUB_FILE_TYPE_HASH_TRUST,
/* Keyboard layout. */
GRUB_FILE_TYPE_KEYBOARD_LAYOUT,
/* Picture file. */