acpi: Disable ACPI table override if securelevel is set

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 securelevel is set.

Signed-off-by: Linn Crosetto <linn@hpe.com>
[bwh: Forward-ported to 4.7: ACPI override code moved to drivers/acpi/tables.c]
[bwh: Forward-ported to 4.9: adjust context]

Gbp-Pq: Topic features/all/securelevel
Gbp-Pq: Name acpi-disable-acpi-table-override-if-securelevel-is-s.patch

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index c1922b2072ec2bfe713bde63cedec239d3a6ea1f..1eded5d9b5d14f3bdcd50e8fb184915649746428 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1160,6 +1160,12 @@ void __init setup_arch(char **cmdline_p)
        /* Allocate bigger log buffer */
        setup_log_buf(1);
 
+#ifdef CONFIG_EFI_SECURE_BOOT_SECURELEVEL
+       if (boot_params.secure_boot) {
+               set_securelevel(1);
+       }
+#endif
+
        reserve_initrd();
 
        acpi_table_upgrade();
@@ -1168,12 +1174,6 @@ void __init setup_arch(char **cmdline_p)
 
        io_delay_init();
 
-#ifdef CONFIG_EFI_SECURE_BOOT_SECURELEVEL
-       if (boot_params.secure_boot) {
-               set_securelevel(1);
-       }
-#endif
-
        /*
         * Parse the ACPI tables for possible boot-time SMP configuration.
         */

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index cdd56c4657e05ff38ed8e11da59d0c37a91326d6..1d493f12eea629035f8bafc8b977d768a50610db 100644 (file)
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -35,6 +35,7 @@
 #include <linux/earlycpio.h>
 #include <linux/memblock.h>
 #include <linux/initrd.h>
+#include <linux/security.h>
 #include "internal.h"
 
 #ifdef CONFIG_ACPI_CUSTOM_DSDT
@@ -545,6 +546,12 @@ void __init acpi_table_upgrade(void)
        if (table_nr == 0)
                return;
 
+       if (get_securelevel() > 0) {
+               pr_notice(PREFIX
+                       "securelevel enabled, ignoring table override\n");
+               return;
+       }
+
        acpi_tables_addr =
                memblock_find_in_range(0, ACPI_TABLE_UPGRADE_MAX_PHYS,
                                       all_tables_size, PAGE_SIZE);