UBUNTU: SAUCE: (efi-lockdown) acpi: Disable ACPI table override if the kernel is...

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>
(cherry picked from commit 95c6461495bf8d85daa48d77d29c36852b7b8bab
 git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index ff425390bfa8d24b6c089a8cb427210a70740ad4..c72bfa97888ab0b668a501d47f6d273a68ec77f5 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()) {
+               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);