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 849c4fb19b033f54a93db411d150e5fce9b6efc6..6c5ee7e66842b06a2402c1212db9cdcc704d8503 100644 (file)
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -527,6 +527,11 @@ 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);