From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Daniel Axtens <dja@axtens.net>

Date: Wed, 29 Jul 2020 17:46:16 +1000

Subject: [PATCH] verifiers: provide unsafe module list

Other verifiers that implement secure boot may want to be able to

use this list and behaviour.

Upstream, this factors the list out of the shim_lock verifier.

However, that hasn't hit the RHEL8.4 tree yet, so instead

of factoring it out of that we just create it.

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

---

 grub-core/commands/verifiers.c | 46 ++++++++++++++++++++++++++++++++++++++++++

 include/grub/verify.h          | 13 ++++++++++++

 2 files changed, 59 insertions(+)

diff --git a/grub-core/commands/verifiers.c b/grub-core/commands/verifiers.c

index 599d79b75..f64343ac9 100644

--- a/grub-core/commands/verifiers.c

+++ b/grub-core/commands/verifiers.c

@@ -218,6 +218,52 @@ grub_verify_string (char *str, enum grub_verify_string_type type)

   return GRUB_ERR_NONE;

 }

+/* List of modules which may allow for verifcation to be bypassed. */

+static const char *const disabled_mods[] = { "iorw", "memrw", "wrmsr", NULL };

+

+/*

+ * Does the module in file `io' allow for the a verifier to be bypassed?

+ *

+ * Returns 1 if so, otherwise 0.

+ */

+char

+grub_is_dangerous_module (grub_file_t io)

+{

+  char *b, *e;

+  int i;

+

+  /* Establish GRUB module name. */

+  b = grub_strrchr (io->name, '/');

+  e = grub_strrchr (io->name, '.');

+

+  b = b ? (b + 1) : io->name;

+  e = e ? e : io->name + grub_strlen (io->name);

+  e = (e > b) ? e : io->name + grub_strlen (io->name);

+

+  for (i = 0; disabled_mods[i]; i++)

+    if (!grub_strncmp (b, disabled_mods[i],

+		       grub_strlen (b) - grub_strlen (e)))

+      return 1;

+  return 0;

+}

+

+/*

+ * Is there already an unsafe module in memory?

+ * Returns the name if one is loaded, otherwise NULL.

+ */

+const char *

+grub_dangerous_module_loaded (void)

+{

+  int i;

+

+  for (i = 0; disabled_mods[i]; i++)

+    if (grub_dl_get (disabled_mods[i]))

+      {

+	return disabled_mods[i];

+      }

+  return NULL;

+}

+

 GRUB_MOD_INIT(verifiers)

 {

   grub_file_filter_register (GRUB_FILE_FILTER_VERIFY, grub_verifiers_open);

diff --git a/include/grub/verify.h b/include/grub/verify.h

index 79022b422..60c13e7ea 100644

--- a/include/grub/verify.h

+++ b/include/grub/verify.h

@@ -76,3 +76,16 @@ grub_verifier_unregister (struct grub_file_verifier *ver)

 grub_err_t

 grub_verify_string (char *str, enum grub_verify_string_type type);

+

+/*

+ * Does the module in file `io' allow for the a verifier to be bypassed?

+ *

+ * Returns 1 if so, otherwise 0.

+ */

+char grub_is_dangerous_module (grub_file_t io);

+

+/*

+ * Is there already an unsafe module in memory?

+ * Returns the name if one is loaded, otherwise NULL.

+ */

+const char *grub_dangerous_module_loaded (void);