[SECURITY PATCH 007/117] acpi: Don't register the acpi command when locked down

[Daniel Kiper]

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

The command is not allowed when lockdown is enforced. Otherwise an
attacker can instruct the GRUB to load an SSDT table to overwrite
the kernel lockdown configuration and later load and execute
unsigned code.

Fixes: CVE-2020-14372

Reported-by: Máté Kukri <km@mkukri.xyz>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 docs/grub.texi            |  5 +++++
 grub-core/commands/acpi.c | 15 ++++++++-------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/docs/grub.texi b/docs/grub.texi
index c3e015d4f..4ce31c2d4 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -4074,6 +4074,11 @@ Normally, this command will replace the Root System 
Description Pointer
 (RSDP) in the Extended BIOS Data Area to point to the new tables. If the
 @option{--no-ebda} option is used, the new tables will be known only to
 GRUB, but may be used by GRUB's EFI emulation.
+
+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
+      Otherwise an attacker can instruct the GRUB to load an SSDT table to
+      overwrite the kernel lockdown configuration and later load and execute
+      unsigned code.
 @end deffn
 
 
diff --git a/grub-core/commands/acpi.c b/grub-core/commands/acpi.c
index 5a1499aa0..1215f2a62 100644
--- a/grub-core/commands/acpi.c
+++ b/grub-core/commands/acpi.c
@@ -27,6 +27,7 @@
 #include <grub/mm.h>
 #include <grub/memory.h>
 #include <grub/i18n.h>
+#include <grub/lockdown.h>
 
 #ifdef GRUB_MACHINE_EFI
 #include <grub/efi/efi.h>
@@ -775,13 +776,13 @@ static grub_extcmd_t cmd;
 
 GRUB_MOD_INIT(acpi)
 {
-  cmd = grub_register_extcmd ("acpi", grub_cmd_acpi, 0,
-                             N_("[-1|-2] [--exclude=TABLE1,TABLE2|"
-                             "--load-only=TABLE1,TABLE2] FILE1"
-                             " [FILE2] [...]"),
-                             N_("Load host ACPI tables and tables "
-                             "specified by arguments."),
-                             options);
+  cmd = grub_register_extcmd_lockdown ("acpi", grub_cmd_acpi, 0,
+                                       N_("[-1|-2] [--exclude=TABLE1,TABLE2|"
+                                          "--load-only=TABLE1,TABLE2] FILE1"
+                                          " [FILE2] [...]"),
+                                       N_("Load host ACPI tables and tables "
+                                          "specified by arguments."),
+                                       options);
 }
 
 GRUB_MOD_FINI(acpi)
-- 
2.11.0