From: David Howells <dhowells@redhat.com>
Date: Wed, 5 Apr 2017 16:40:29 +0000 (+0100)
Subject: efi: Lock down the kernel if booted in secure boot mode
X-Git-Tag: archive/raspbian/4.15.4-1+rpi1~1^2^2~69
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=b260cec752b881839074a310a0dcc8c20a6ff18d;p=linux.git

efi: Lock down the kernel if booted in secure boot mode

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 <dhowells@redhat.com>

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0040-efi-Lock-down-the-kernel-if-booted-in-secure-boot-mo.patch
---

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 77f6df85d30..ae59d95aab3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1887,6 +1887,18 @@ 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 b3f8350b34f..e6a2155651c 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -70,6 +70,7 @@
 #include <linux/tboot.h>
 #include <linux/jiffies.h>
 #include <linux/mem_encrypt.h>
+#include <linux/security.h>
 
 #include <linux/usb/xhci-dbgp.h>
 #include <video/edid.h>
@@ -1204,7 +1205,12 @@ 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");