From d1a40f870dbcb55280f57673c1d9c2c7110df42a Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Wed, 24 Feb 2021 09:00:05 +0100
Subject: [PATCH 15/46] commands: Restrict commands that can load BIOS or DT
 blobs when locked down

There are some more commands that should be restricted when the GRUB is
locked down. Following is the list of commands and reasons to restrict:

  * fakebios:   creates BIOS-like structures for backward compatibility with
                existing OSes. This should not be allowed when locked down.

  * loadbios:   reads a BIOS dump from storage and loads it. This action
                should not be allowed when locked down.

  * devicetree: loads a Device Tree blob and passes it to the OS. It replaces
                any Device Tree provided by the firmware. This also should
                not be allowed when locked down.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 docs/grub.texi                    |  3 +++
 grub-core/commands/efi/loadbios.c | 16 ++++++++--------
 grub-core/loader/arm/linux.c      |  6 +++---
 grub-core/loader/efi/fdt.c        |  4 ++--
 4 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/docs/grub.texi b/docs/grub.texi
index 70bf91f40..cf29a1797 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4236,6 +4236,9 @@ Load a device tree blob (.dtb) from a filesystem, for later use by a Linux
 kernel. Does not perform merging with any device tree supplied by firmware,
 but rather replaces it completely.
 @ref{GNU/Linux}.
+
+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
+      This is done to prevent subverting various security mechanisms.
 @end deffn
 
 @node distrust
diff --git a/grub-core/commands/efi/loadbios.c b/grub-core/commands/efi/loadbios.c
index d41d521a4..5c7725f8b 100644
--- a/grub-core/commands/efi/loadbios.c
+++ b/grub-core/commands/efi/loadbios.c
@@ -205,14 +205,14 @@ static grub_command_t cmd_fakebios, cmd_loadbios;
 
 GRUB_MOD_INIT(loadbios)
 {
-  cmd_fakebios = grub_register_command ("fakebios", grub_cmd_fakebios,
-					0, N_("Create BIOS-like structures for"
-					      " backward compatibility with"
-					      " existing OS."));
-
-  cmd_loadbios = grub_register_command ("loadbios", grub_cmd_loadbios,
-					N_("BIOS_DUMP [INT10_DUMP]"),
-					N_("Load BIOS dump."));
+  cmd_fakebios = grub_register_command_lockdown ("fakebios", grub_cmd_fakebios,
+						 0, N_("Create BIOS-like structures for"
+						       " backward compatibility with"
+						       " existing OS."));
+
+  cmd_loadbios = grub_register_command_lockdown ("loadbios", grub_cmd_loadbios,
+						 N_("BIOS_DUMP [INT10_DUMP]"),
+						 N_("Load BIOS dump."));
 }
 
 GRUB_MOD_FINI(loadbios)
diff --git a/grub-core/loader/arm/linux.c b/grub-core/loader/arm/linux.c
index d70c17486..ed23dc71e 100644
--- a/grub-core/loader/arm/linux.c
+++ b/grub-core/loader/arm/linux.c
@@ -493,9 +493,9 @@ GRUB_MOD_INIT (linux)
 				     0, N_("Load Linux."));
   cmd_initrd = grub_register_command ("initrd", grub_cmd_initrd,
 				      0, N_("Load initrd."));
-  cmd_devicetree = grub_register_command ("devicetree", grub_cmd_devicetree,
-					  /* TRANSLATORS: DTB stands for device tree blob.  */
-					  0, N_("Load DTB file."));
+  cmd_devicetree = grub_register_command_lockdown ("devicetree", grub_cmd_devicetree,
+						   /* TRANSLATORS: DTB stands for device tree blob. */
+						   0, N_("Load DTB file."));
   my_mod = mod;
   current_fdt = (const void *) grub_arm_firmware_get_boot_data ();
   machine_type = grub_arm_firmware_get_machine_type ();
diff --git a/grub-core/loader/efi/fdt.c b/grub-core/loader/efi/fdt.c
index ee9c5592c..003d07cd8 100644
--- a/grub-core/loader/efi/fdt.c
+++ b/grub-core/loader/efi/fdt.c
@@ -165,8 +165,8 @@ static grub_command_t cmd_devicetree;
 GRUB_MOD_INIT (fdt)
 {
   cmd_devicetree =
-    grub_register_command ("devicetree", grub_cmd_devicetree, 0,
-			   N_("Load DTB file."));
+    grub_register_command_lockdown ("devicetree", grub_cmd_devicetree, 0,
+				    N_("Load DTB file."));
 }
 
 GRUB_MOD_FINI (fdt)
-- 
2.26.2