From 0000000000000000000000000000000000000000 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] 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>
---
 grub-core/commands/efi/loadbios.c | 14 +++++++-------
 grub-core/loader/arm/linux.c      |  6 +++---
 docs/grub.texi                    |  6 ++++--
 3 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/grub-core/commands/efi/loadbios.c b/grub-core/commands/efi/loadbios.c
index 132cadbc764..3da4c26df7a 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_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 ("loadbios", grub_cmd_loadbios,
-					N_("BIOS_DUMP [INT10_DUMP]"),
-					N_("Load BIOS dump."));
+  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 1b195e0899e..8fc905e26ca 100644
--- a/grub-core/loader/arm/linux.c
+++ b/grub-core/loader/arm/linux.c
@@ -513,9 +513,9 @@ 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;
   fdt_addr = (void *) grub_arm_firmware_get_boot_data ();
   machine_type = grub_arm_firmware_get_machine_type ();
diff --git a/docs/grub.texi b/docs/grub.texi
index 5a1cfd4aea9..432610991b7 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4157,13 +4157,15 @@ hour, minute, and second unchanged.
 
 
 @node devicetree
-@subsection linux
+@subsection devicetree
 
 @deffn Command devicetree file
 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