[PATCH v3 16/19] appended signatures: support verifying appended signatures

[Daniel Axtens]

Building on the parsers and the ability to embed x509 certificates, as
well as the existing gcrypt functionality, add a module for verifying
appended signatures.

This includes a verifier that requires that Linux kernels and grub modules
have appended signatures, and commands to manage the list of trusted
certificates for verification.

Verification must be enabled by setting check_appended_signatures. If
GRUB is locked down when the module is loaded, verification will be
enabled and locked automatically.

As with the PGP verifier, it is not a complete secure-boot solution:
other mechanisms, such as a password or lockdown, must be used to ensure
that a user cannot drop to the grub shell and disable verification.

Signed-off-by: Daniel Axtens <dja@axtens.net>

---

v3: Correct copyright header, fix some nits from Stefan.

v2 changes:

 - Improve x509 parser function name
 - Constify data parameters in function signatures
 - Support multiple signers
 - Use an enum rather than 0, 1 and 2 for various signature
    enforcement states.
 - Spin out a file reading function that was duplicated.
 - Fix some code style and clarity issues.

Thanks to Nayna Jain and Stefan Berger for their reviews.
---
 grub-core/Makefile.core.def                  |  14 +
 grub-core/commands/appendedsig/appendedsig.c | 662 +++++++++++++++++++
 include/grub/file.h                          |   2 +
 3 files changed, 678 insertions(+)
 create mode 100644 grub-core/commands/appendedsig/appendedsig.c

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index de5c763c64a0..2dc450a83398 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -951,6 +951,20 @@ module = {
   cppflags = '-I$(srcdir)/lib/posix_wrap';
 };
 
+module = {
+  name = appendedsig;
+  common = commands/appendedsig/appendedsig.c;
+  common = commands/appendedsig/x509.c;
+  common = commands/appendedsig/pkcs7.c;
+  common = commands/appendedsig/asn1util.c;
+  common = commands/appendedsig/gnutls_asn1_tab.c;
+  common = commands/appendedsig/pkix_asn1_tab.c;
+
+  // posix wrapper required for gcry to get sys/types.h
+  cflags = '$(CFLAGS_POSIX)';
+  cppflags = '-I$(srcdir)/lib/posix_wrap';
+};
+
 module = {
   name = hdparm;
   common = commands/hdparm.c;
diff --git a/grub-core/commands/appendedsig/appendedsig.c 
b/grub-core/commands/appendedsig/appendedsig.c
new file mode 100644
index 000000000000..d2e19c268204
--- /dev/null
+++ b/grub-core/commands/appendedsig/appendedsig.c
@@ -0,0 +1,662 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2020, 2021, 2022 Free Software Foundation, Inc.
+ *  Copyright (C) 2020, 2021, 2022 IBM Corporation
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/types.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+#include <grub/err.h>
+#include <grub/dl.h>
+#include <grub/file.h>
+#include <grub/command.h>
+#include <grub/crypto.h>
+#include <grub/pkcs1_v15.h>
+#include <grub/i18n.h>
+#include <grub/gcrypt/gcrypt.h>
+#include <grub/kernel.h>
+#include <grub/extcmd.h>
+#include <grub/verify.h>
+#include <grub/libtasn1.h>
+#include <grub/env.h>
+#include <grub/lockdown.h>
+
+#include "appendedsig.h"
+
+GRUB_MOD_LICENSE ("GPLv3+");
+
+const char magic[] = "~Module signature appended~\n";
+
+/*
+ * This structure is extracted from scripts/sign-file.c in the linux kernel
+ * source. It was licensed as LGPLv2.1+, which is GPLv3+ compatible.
+ */
+struct module_signature
+{
+  grub_uint8_t algo;           /* Public-key crypto algorithm [0] */
+  grub_uint8_t hash;           /* Digest algorithm [0] */
+  grub_uint8_t id_type;                /* Key identifier type [PKEY_ID_PKCS7] 
*/
+  grub_uint8_t signer_len;     /* Length of signer's name [0] */
+  grub_uint8_t key_id_len;     /* Length of key identifier [0] */
+  grub_uint8_t __pad[3];
+  grub_uint32_t sig_len;       /* Length of signature data */
+} GRUB_PACKED;
+
+
+/* This represents an entire, parsed, appended signature */
+struct grub_appended_signature
+{
+  grub_size_t signature_len;           /* Length of PKCS#7 data +
+                                         * metadata + magic */
+
+  struct module_signature sig_metadata;        /* Module signature metadata */
+  struct pkcs7_signedData pkcs7;       /* Parsed PKCS#7 data */
+};
+
+/* Trusted certificates for verifying appended signatures */
+struct x509_certificate *grub_trusted_key;
+
+/*
+ * Force gcry_rsa to be a module dependency.
+ *
+ * If we use grub_crypto_pk_rsa, then then the gcry_rsa module won't be built
+ * in if you add 'appendedsig' to grub-install --modules. You would need to
+ * add 'gcry_rsa' too. That's confusing and seems suboptimal, especially when
+ * we only support RSA.
+ *
+ * Dynamic loading also causes some concerns. We can't load gcry_rsa from the
+ * the filesystem after we install the verifier - we won't be able to verify
+ * it without having it already present. We also shouldn't load it before we
+ * install the verifier, because that would mean it wouldn't be verified - an
+ * attacker could insert any code they wanted into the module.
+ *
+ * So instead, reference the internal symbol from gcry_rsa. That creates a
+ * direct dependency on gcry_rsa, so it will be built in when this module
+ * is built in. Being built in (assuming the core image is itself signed!)
+ * also resolves our concerns about loading from the filesystem.
+ */
+extern gcry_pk_spec_t _gcry_pubkey_spec_rsa;
+
+static enum
+{
+  check_sigs_no = 0,
+  check_sigs_enforce = 1,
+  check_sigs_forced = 2
+} check_sigs = check_sigs_no;
+
+static const char *
+grub_env_read_sec (struct grub_env_var *var __attribute__((unused)),
+                  const char *val __attribute__((unused)))
+{
+  if (check_sigs == check_sigs_forced)
+    return "forced";
+  else if (check_sigs == check_sigs_enforce)
+    return "enforce";
+  else
+    return "no";
+}
+
+static char *
+grub_env_write_sec (struct grub_env_var *var __attribute__((unused)),
+                   const char *val)
+{
+  /* Do not allow the value to be changed if set to forced */
+  if (check_sigs == check_sigs_forced)
+    return grub_strdup ("forced");
+
+  if ((*val == '2') || (*val == 'f'))
+    check_sigs = check_sigs_forced;
+  else if ((*val == '1') || (*val == 'e'))
+    check_sigs = check_sigs_enforce;
+  else if ((*val == '0') || (*val == 'n'))
+    check_sigs = check_sigs_no;
+
+  return grub_strdup (grub_env_read_sec (NULL, NULL));
+}
+
+static grub_err_t
+file_read_all (grub_file_t file, grub_uint8_t **buf, grub_size_t *len)
+{
+  grub_off_t full_file_size;
+  grub_size_t file_size, total_read_size = 0;
+  grub_ssize_t read_size;
+
+  full_file_size = grub_file_size (file);
+  if (full_file_size == GRUB_FILE_SIZE_UNKNOWN)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                      N_("Cannot read a file of unknown size into a buffer"));
+
+  if (full_file_size > GRUB_SIZE_MAX)
+    return grub_error (GRUB_ERR_OUT_OF_RANGE,
+                      N_("File is too large to read: %" PRIuGRUB_UINT64_T
+                         " bytes"), full_file_size);
+
+  file_size = (grub_size_t) full_file_size;
+
+  *buf = grub_malloc (file_size);
+  if (!*buf)
+    return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+                      N_("Could not allocate file data buffer size %"
+                         PRIuGRUB_SIZE), file_size);
+
+  while (total_read_size < file_size)
+    {
+      read_size =
+       grub_file_read (file, *buf + total_read_size,
+                       file_size - total_read_size);
+
+      if (read_size < 0)
+       {
+         grub_free (*buf);
+         return grub_errno;
+       }
+      else if (read_size == 0)
+       {
+         grub_free (*buf);
+         return grub_error (GRUB_ERR_IO,
+                            N_("Could not read full file size (%"
+                               PRIuGRUB_SIZE "), only %" PRIuGRUB_SIZE
+                               " bytes read"), file_size, total_read_size);
+       }
+
+      total_read_size += read_size;
+    }
+  *len = file_size;
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+read_cert_from_file (grub_file_t f, struct x509_certificate *certificate)
+{
+  grub_err_t err;
+  grub_uint8_t *buf;
+  grub_size_t file_size;
+
+  err = file_read_all (f, &buf, &file_size);
+  if (err != GRUB_ERR_NONE)
+    return err;
+
+  err = parse_x509_certificate (buf, file_size, certificate);
+  grub_free (buf);
+
+  return err;
+}
+
+static grub_err_t
+extract_appended_signature (const grub_uint8_t *buf, grub_size_t bufsize,
+                           struct grub_appended_signature *sig)
+{
+  grub_size_t pkcs7_size;
+  grub_size_t remaining_len;
+  const grub_uint8_t *appsigdata = buf + bufsize - grub_strlen (magic);
+
+  if (bufsize < grub_strlen (magic))
+    return grub_error (GRUB_ERR_BAD_SIGNATURE,
+                      N_("File too short for signature magic"));
+
+  if (grub_memcmp (appsigdata, (grub_uint8_t *) magic, grub_strlen (magic)))
+    return grub_error (GRUB_ERR_BAD_SIGNATURE,
+                      N_("Missing or invalid signature magic"));
+
+  remaining_len = bufsize - grub_strlen (magic);
+
+  if (remaining_len < sizeof (struct module_signature))
+    return grub_error (GRUB_ERR_BAD_SIGNATURE,
+                      N_("File too short for signature metadata"));
+
+  appsigdata -= sizeof (struct module_signature);
+
+  /* extract the metadata */
+  grub_memcpy (&(sig->sig_metadata), appsigdata,
+              sizeof (struct module_signature));
+
+  remaining_len -= sizeof (struct module_signature);
+
+  if (sig->sig_metadata.id_type != 2)
+    return grub_error (GRUB_ERR_BAD_SIGNATURE, N_("Wrong signature type"));
+
+  pkcs7_size = grub_be_to_cpu32 (sig->sig_metadata.sig_len);
+
+  if (pkcs7_size > remaining_len)
+    return grub_error (GRUB_ERR_BAD_SIGNATURE,
+                      N_("File too short for PKCS#7 message"));
+
+  grub_dprintf ("appendedsig", "sig len %" PRIuGRUB_SIZE "\n", pkcs7_size);
+
+  sig->signature_len =
+    grub_strlen (magic) + sizeof (struct module_signature) + pkcs7_size;
+
+  /* rewind pointer and parse pkcs7 data */
+  appsigdata -= pkcs7_size;
+
+  return parse_pkcs7_signedData (appsigdata, pkcs7_size, &sig->pkcs7);
+}
+
+static grub_err_t
+grub_verify_appended_signature (const grub_uint8_t *buf, grub_size_t bufsize)
+{
+  grub_err_t err = GRUB_ERR_NONE;
+  grub_size_t datasize;
+  void *context;
+  unsigned char *hash;
+  gcry_mpi_t hashmpi;
+  gcry_err_code_t rc;
+  struct x509_certificate *pk;
+  struct grub_appended_signature sig;
+  struct pkcs7_signerInfo *si;
+  int i;
+
+  if (!grub_trusted_key)
+    return grub_error (GRUB_ERR_BAD_SIGNATURE,
+                      N_("No trusted keys to verify against"));
+
+  err = extract_appended_signature (buf, bufsize, &sig);
+  if (err != GRUB_ERR_NONE)
+    return err;
+
+  datasize = bufsize - sig.signature_len;
+
+  for (i = 0; i < sig.pkcs7.signerInfo_count; i++)
+    {
+      /* 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 = grub_trusted_key; pk; pk = pk->next)
+       {
+         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)
+           {
+             grub_dprintf ("appendedsig",
+                           "verify signer %d with key '%s' succeeded\n", i,
+                           pk->subject);
+             err = GRUB_ERR_NONE;
+             break;
+           }
+
+         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;
+    }
+
+  /* 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);
+
+  return err;
+}
+
+static grub_err_t
+grub_cmd_verify_signature (grub_command_t cmd __attribute__((unused)),
+                          int argc, char **args)
+{
+  grub_file_t f;
+  grub_err_t err = GRUB_ERR_NONE;
+  grub_uint8_t *data;
+  grub_size_t file_size;
+
+  if (argc < 1)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument expected"));
+
+  grub_dprintf ("appendedsig", "verifying %s\n", args[0]);
+
+  f = grub_file_open (args[0], GRUB_FILE_TYPE_VERIFY_SIGNATURE);
+  if (!f)
+    {
+      err = grub_errno;
+      goto cleanup;
+    }
+
+  err = file_read_all (f, &data, &file_size);
+  if (err != GRUB_ERR_NONE)
+    goto cleanup;
+
+  err = grub_verify_appended_signature (data, file_size);
+
+  grub_free (data);
+
+cleanup:
+  if (f)
+    grub_file_close (f);
+  return err;
+}
+
+static grub_err_t
+grub_cmd_distrust (grub_command_t cmd __attribute__((unused)),
+                  int argc, char **args)
+{
+  unsigned long cert_num, i;
+  struct x509_certificate *cert, *prev;
+
+  if (argc != 1)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("One argument expected"));
+
+  grub_errno = GRUB_ERR_NONE;
+  cert_num = grub_strtoul (args[0], NULL, 10);
+  if (grub_errno != GRUB_ERR_NONE)
+    return grub_errno;
+
+  if (cert_num < 1)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                      N_("Certificate number too small - numbers start at 1"));
+
+  if (cert_num == 1)
+    {
+      cert = grub_trusted_key;
+      grub_trusted_key = cert->next;
+
+      certificate_release (cert);
+      grub_free (cert);
+      return GRUB_ERR_NONE;
+    }
+  i = 2;
+  prev = grub_trusted_key;
+  cert = grub_trusted_key->next;
+  while (cert)
+    {
+      if (i == cert_num)
+       {
+         prev->next = cert->next;
+         certificate_release (cert);
+         grub_free (cert);
+         return GRUB_ERR_NONE;
+       }
+      i++;
+      prev = cert;
+      cert = cert->next;
+    }
+
+  return grub_error (GRUB_ERR_BAD_ARGUMENT,
+                    N_("No certificate number %lu found - only %lu 
certificates in the store"),
+                    cert_num, i - 1);
+}
+
+static grub_err_t
+grub_cmd_trust (grub_command_t cmd __attribute__((unused)),
+               int argc, char **args)
+{
+  grub_file_t certf;
+  struct x509_certificate *cert = NULL;
+  grub_err_t err;
+
+  if (argc != 1)
+    return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("one argument expected"));
+
+  certf = grub_file_open (args[0],
+                         GRUB_FILE_TYPE_CERTIFICATE_TRUST
+                         | GRUB_FILE_TYPE_NO_DECOMPRESS);
+  if (!certf)
+    return grub_errno;
+
+
+  cert = grub_zalloc (sizeof (struct x509_certificate));
+  if (!cert)
+    return grub_error (GRUB_ERR_OUT_OF_MEMORY,
+                      N_("Could not allocate memory for certificate"));
+
+  err = read_cert_from_file (certf, cert);
+  grub_file_close (certf);
+  if (err != GRUB_ERR_NONE)
+    {
+      grub_free (cert);
+      return err;
+    }
+  grub_dprintf ("appendedsig", "Loaded certificate with CN: %s\n",
+               cert->subject);
+
+  cert->next = grub_trusted_key;
+  grub_trusted_key = cert;
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+grub_cmd_list (grub_command_t cmd __attribute__((unused)),
+              int argc __attribute__((unused)),
+              char **args __attribute__((unused)))
+{
+  struct x509_certificate *cert;
+  int cert_num = 1;
+  grub_size_t i;
+
+  for (cert = grub_trusted_key; cert; cert = cert->next)
+    {
+      grub_printf (N_("Certificate %d:\n"), cert_num);
+
+      grub_printf (N_("\tSerial: "));
+      for (i = 0; i < cert->serial_len - 1; i++)
+       {
+         grub_printf ("%02x:", cert->serial[i]);
+       }
+      grub_printf ("%02x\n", cert->serial[cert->serial_len - 1]);
+
+      grub_printf ("\tCN: %s\n\n", cert->subject);
+      cert_num++;
+
+    }
+
+  return GRUB_ERR_NONE;
+}
+
+static grub_err_t
+appendedsig_init (grub_file_t io __attribute__((unused)),
+                 enum grub_file_type type,
+                 void **context __attribute__((unused)),
+                 enum grub_verify_flags *flags)
+{
+  if (check_sigs == check_sigs_no)
+    {
+      *flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
+      return GRUB_ERR_NONE;
+    }
+
+  switch (type & GRUB_FILE_TYPE_MASK)
+    {
+    case GRUB_FILE_TYPE_CERTIFICATE_TRUST:
+      /*
+       * This is a certificate to add to trusted keychain.
+       *
+       * This needs to be verified or blocked. Ideally we'd write an x509
+       * verifier, but we lack the hubris required to take this on. Instead,
+       * require that it have an appended signature.
+       */
+
+      /* Fall through */
+
+    case GRUB_FILE_TYPE_LINUX_KERNEL:
+    case GRUB_FILE_TYPE_GRUB_MODULE:
+      /*
+       * Appended signatures are only defined for ELF binaries.
+       * Out of an abundance of caution, we only verify Linux kernels and
+       * GRUB modules at this point.
+       */
+      *flags = GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
+      return GRUB_ERR_NONE;
+
+    case GRUB_FILE_TYPE_ACPI_TABLE:
+    case GRUB_FILE_TYPE_DEVICE_TREE_IMAGE:
+      /*
+       * It is possible to use appended signature verification without
+       * lockdown - like the PGP verifier. When combined with an embedded
+       * config file in a signed grub binary, this could still be a meaningful
+       * secure-boot chain - so long as it isn't subverted by something like a
+       * rouge ACPI table or DT image. Defer them explicitly.
+       */
+      *flags = GRUB_VERIFY_FLAGS_DEFER_AUTH;
+      return GRUB_ERR_NONE;
+
+    default:
+      *flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
+      return GRUB_ERR_NONE;
+    }
+}
+
+static grub_err_t
+appendedsig_write (void *ctxt __attribute__((unused)),
+                  void *buf, grub_size_t size)
+{
+  return grub_verify_appended_signature (buf, size);
+}
+
+struct grub_file_verifier grub_appendedsig_verifier = {
+  .name = "appendedsig",
+  .init = appendedsig_init,
+  .write = appendedsig_write,
+};
+
+static grub_ssize_t
+pseudo_read (struct grub_file *file, char *buf, grub_size_t len)
+{
+  grub_memcpy (buf, (grub_uint8_t *) file->data + file->offset, len);
+  return len;
+}
+
+/* Filesystem descriptor.  */
+static struct grub_fs pseudo_fs = {
+  .name = "pseudo",
+  .fs_read = pseudo_read
+};
+
+static grub_command_t cmd_verify, cmd_list, cmd_distrust, cmd_trust;
+
+GRUB_MOD_INIT (appendedsig)
+{
+  int rc;
+  struct grub_module_header *header;
+
+  /* If in lockdown, immediately enter forced mode */
+  if (grub_is_lockdown () == GRUB_LOCKDOWN_ENABLED)
+    check_sigs = check_sigs_forced;
+
+  grub_trusted_key = NULL;
+
+  grub_register_variable_hook ("check_appended_signatures",
+                              grub_env_read_sec, grub_env_write_sec);
+  grub_env_export ("check_appended_signatures");
+
+  rc = asn1_init ();
+  if (rc)
+    grub_fatal ("Error initing ASN.1 data structures: %d: %s\n", rc,
+               asn1_strerror (rc));
+
+  FOR_MODULES (header)
+  {
+    struct grub_file pseudo_file;
+    struct x509_certificate *pk = NULL;
+    grub_err_t err;
+
+    /* Not an X.509 certificate, skip. */
+    if (header->type != OBJ_TYPE_X509_PUBKEY)
+      continue;
+
+    grub_memset (&pseudo_file, 0, sizeof (pseudo_file));
+    pseudo_file.fs = &pseudo_fs;
+    pseudo_file.size = header->size - sizeof (struct grub_module_header);
+    pseudo_file.data = (char *) header + sizeof (struct grub_module_header);
+
+    grub_dprintf ("appendedsig",
+                 "Found an x509 key, size=%" PRIuGRUB_UINT64_T "\n",
+                 pseudo_file.size);
+
+    pk = grub_zalloc (sizeof (struct x509_certificate));
+    if (!pk)
+      {
+       grub_fatal ("Out of memory loading initial certificates");
+      }
+
+    err = read_cert_from_file (&pseudo_file, pk);
+    if (err != GRUB_ERR_NONE)
+      grub_fatal ("Error loading initial key: %s", grub_errmsg);
+
+    grub_dprintf ("appendedsig", "loaded certificate CN='%s'\n", pk->subject);
+
+    pk->next = grub_trusted_key;
+    grub_trusted_key = pk;
+  }
+
+  cmd_trust =
+    grub_register_command ("trust_certificate", grub_cmd_trust,
+                          N_("X509_CERTIFICATE"),
+                          N_("Add X509_CERTIFICATE to trusted certificates."));
+  cmd_list =
+    grub_register_command ("list_certificates", grub_cmd_list, 0,
+                          N_("Show the list of trusted x509 certificates."));
+  cmd_verify =
+    grub_register_command ("verify_appended", grub_cmd_verify_signature,
+                          N_("FILE"),
+                          N_("Verify FILE against the trusted x509 
certificates."));
+  cmd_distrust =
+    grub_register_command ("distrust_certificate", grub_cmd_distrust,
+                          N_("CERT_NUMBER"),
+                          N_("Remove CERT_NUMBER (as listed by 
list_certificates) from trusted certificates."));
+
+  grub_verifier_register (&grub_appendedsig_verifier);
+  grub_dl_set_persistent (mod);
+}
+
+GRUB_MOD_FINI (appendedsig)
+{
+  /*
+   * grub_dl_set_persistent should prevent this from actually running, but
+   * it does still run under emu.
+   */
+
+  grub_verifier_unregister (&grub_appendedsig_verifier);
+  grub_unregister_command (cmd_verify);
+  grub_unregister_command (cmd_list);
+  grub_unregister_command (cmd_trust);
+  grub_unregister_command (cmd_distrust);
+}
diff --git a/include/grub/file.h b/include/grub/file.h
index 31567483ccfc..96827a4f8961 100644
--- a/include/grub/file.h
+++ b/include/grub/file.h
@@ -80,6 +80,8 @@ enum grub_file_type
     GRUB_FILE_TYPE_PUBLIC_KEY,
     /* File holding public key to add to trused keys.  */
     GRUB_FILE_TYPE_PUBLIC_KEY_TRUST,
+    /* File holding x509 certificiate to add to trusted keys.  */
+    GRUB_FILE_TYPE_CERTIFICATE_TRUST,
     /* File of which we intend to print a blocklist to the user.  */
     GRUB_FILE_TYPE_PRINT_BLOCKLIST,
     /* File we intend to use for test loading or testing speed.  */
-- 
2.32.0