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>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0056-acpi-Disable-ACPI-table-override-if-the-kernel-is-lo.patch

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 2604189d6cd156e5449c7dd071d63120ea000a0e..601096d0d8492692b940219576c89de95968c7df 100644 (file)
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -542,6 +542,11 @@ 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);