From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Wed, 14 Oct 2020 16:33:42 +0200
Subject: [PATCH] mmap: Don't register cutmem and badram commands when lockdown
 is enforced

The cutmem and badram commands can be used to remove EFI memory regions
and potentially disable the UEFI Secure Boot. Prevent the commands to be
registered if the GRUB is locked down.

Fixes: CVE-2020-27779

Reported-by: Teddy Reed <teddy.reed@gmail.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/mmap/mmap.c | 13 +++++++------
 docs/grub.texi        |  4 ++++
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/grub-core/mmap/mmap.c b/grub-core/mmap/mmap.c
index 57b4e9a72a9..7ebf32e1e5e 100644
--- a/grub-core/mmap/mmap.c
+++ b/grub-core/mmap/mmap.c
@@ -20,6 +20,7 @@
 #include <grub/memory.h>
 #include <grub/machine/memory.h>
 #include <grub/err.h>
+#include <grub/lockdown.h>
 #include <grub/misc.h>
 #include <grub/mm.h>
 #include <grub/command.h>
@@ -534,12 +535,12 @@ static grub_command_t cmd, cmd_cut;
 
 GRUB_MOD_INIT(mmap)
 {
-  cmd = grub_register_command ("badram", grub_cmd_badram,
-			       N_("ADDR1,MASK1[,ADDR2,MASK2[,...]]"),
-			       N_("Declare memory regions as faulty (badram)."));
-  cmd_cut = grub_register_command ("cutmem", grub_cmd_cutmem,
-				   N_("FROM[K|M|G] TO[K|M|G]"),
-				   N_("Remove any memory regions in specified range."));
+  cmd = grub_register_command_lockdown ("badram", grub_cmd_badram,
+                                        N_("ADDR1,MASK1[,ADDR2,MASK2[,...]]"),
+                                        N_("Declare memory regions as faulty (badram)."));
+  cmd_cut = grub_register_command_lockdown ("cutmem", grub_cmd_cutmem,
+                                            N_("FROM[K|M|G] TO[K|M|G]"),
+                                            N_("Remove any memory regions in specified range."));
 
 }
 
diff --git a/docs/grub.texi b/docs/grub.texi
index 01acf672b80..f1675b6140c 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4103,6 +4103,10 @@ this page is to be filtered.  This syntax makes it easy to represent patterns
 that are often result of memory damage, due to physical distribution of memory
 cells.
 
+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
+      This prevents removing EFI memory regions to potentially subvert the
+      security mechanisms provided by the UEFI secure boot.
+
 @node blocklist
 @subsection blocklist
 
