[SECURITY PATCH 008/117] mmap: Don't register cutmem and badram commands when lockdown is enforced

[Daniel Kiper]

From: Javier Martinez Canillas <javierm@redhat.com>

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>
---
 docs/grub.texi        |  4 ++++
 grub-core/mmap/mmap.c | 13 +++++++------
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/docs/grub.texi b/docs/grub.texi
index 4ce31c2d4..5dbb02f1c 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4139,6 +4139,10 @@ 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
 
diff --git a/grub-core/mmap/mmap.c b/grub-core/mmap/mmap.c
index 64684c23d..3cae68364 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."));
 
 }
 
-- 
2.11.0