[PATCH V40 16/29] acpi: Disable ACPI table override if the kernel is locked down

[Matthew Garrett]

From: Linn Crosetto <lcrosetto at gmail.com>

>From the kernel documentation (initrd_table_override.txt):

  If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
  to override nearly any ACPI table provided by the BIOS with an
  instrumented, modified one.

When lockdown is enabled, the kernel should disallow any unauthenticated
changes to kernel space.  ACPI tables contain code invoked by the kernel,
so do not allow ACPI tables to be overridden if the kernel is locked down.

Signed-off-by: Linn Crosetto <lcrosetto at gmail.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Matthew Garrett <mjg59 at google.com>
Reviewed-by: Kees Cook <keescook at chromium.org>
cc: linux-acpi at vger.kernel.org
Signed-off-by: James Morris <jmorris at namei.org>
---
 drivers/acpi/tables.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index de974322a197..b7c29a11c0c1 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -20,6 +20,7 @@
 #include <linux/memblock.h>
 #include <linux/earlycpio.h>
 #include <linux/initrd.h>
+#include <linux/security.h>
 #include "internal.h"
 
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
@@ -577,6 +578,11 @@ void __init acpi_table_upgrade(void)
 	if (table_nr == 0)
 		return;
 
+	if (security_locked_down(LOCKDOWN_ACPI_TABLES)) {
+		pr_notice("kernel is locked down, ignoring table override\n");
+		return;
+	}
+
 	acpi_tables_addr =
 		memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS,
 				       all_tables_size, PAGE_SIZE);
-- 
2.23.0.rc1.153.gdeed80330f-goog