acpi: Disable ACPI table override if the kernel is locked down

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 securelevel is set, 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 <linn@hpe.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
cc: linux-acpi@vger.kernel.org

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0017-acpi-Disable-ACPI-table-override-if-the-kernel-is-lo.patch

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 80ce2a7d224b63d814420765bef9ff502571ef6d..5cc13c42daf90848a911163d985aa086bd49b970 100644 (file)
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -526,6 +526,11 @@ void __init acpi_table_upgrade(void)
        if (table_nr == 0)
                return;
 
+       if (kernel_is_locked_down("ACPI table override")) {
+               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);