[PATCH 03/24] efi: Lock down the kernel if booted in secure boot mode

[David Howells]

UEFI Secure Boot provides a mechanism for ensuring that the firmware will
only load signed bootloaders and kernels.  Certain use cases may also
require that all kernel modules also be signed.  Add a configuration option
that to lock down the kernel - which includes requiring validly signed
modules - if the kernel is secure-booted.

Signed-off-by: David Howells <dhowe...@redhat.com>
---

 arch/x86/Kconfig        |   12 ++++++++++++
 arch/x86/kernel/setup.c |    8 +++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cc98d5a294ee..21f39855661d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1817,6 +1817,18 @@ config EFI_MIXED
 
           If unsure, say N.
 
+config EFI_SECURE_BOOT_LOCK_DOWN
+       def_bool n
+       depends on EFI
+       prompt "Lock down the kernel when UEFI Secure Boot is enabled"
+       ---help---
+         UEFI Secure Boot provides a mechanism for ensuring that the firmware
+         will only load signed bootloaders and kernels.  Certain use cases may
+         also require that all kernel modules also be signed and that
+         userspace is prevented from directly changing the running kernel
+         image.  Say Y here to automatically lock down the kernel when a
+         system boots with UEFI Secure Boot enabled.
+
 config SECCOMP
        def_bool y
        prompt "Enable seccomp to safely compute untrusted bytecode"
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 396285bddb93..85dfa745c442 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -69,6 +69,7 @@
 #include <linux/crash_dump.h>
 #include <linux/tboot.h>
 #include <linux/jiffies.h>
+#include <linux/security.h>
 
 #include <video/edid.h>
 
@@ -1185,7 +1186,12 @@ void __init setup_arch(char **cmdline_p)
                        break;
                case efi_secureboot_mode_enabled:
                        set_bit(EFI_SECURE_BOOT, &efi.flags);
-                       pr_info("Secure boot enabled\n");
+                       if (IS_ENABLED(CONFIG_EFI_SECURE_BOOT_LOCK_DOWN)) {
+                               lock_kernel_down();
+                               pr_info("Secure boot enabled and kernel locked 
down\n");
+                       } else {
+                               pr_info("Secure boot enabled\n");
+                       }
                        break;
                default:
                        pr_info("Secure boot could not be determined\n");