[PATCH 01/27] Add the ability to lock down access to the running kernel image

[David Howells]

Provide a single call to allow kernel code to determine whether the system
should be locked down, thereby disallowing various accesses that might
allow the running kernel image to be changed including the loading of
modules that aren't validly signed with a key we recognise, fiddling with
MSR registers and disallowing hibernation,

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

 include/linux/kernel.h   |   17 +++++++++++++
 include/linux/security.h |    8 ++++++
 security/Kconfig         |    8 ++++++
 security/Makefile        |    3 ++
 security/lock_down.c     |   60 ++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 96 insertions(+)
 create mode 100644 security/lock_down.c

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0ad4c3044cf9..362da2e4bf53 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -287,6 +287,23 @@ static inline void refcount_error_report(struct pt_regs *regs, const char *err)
 { }
 #endif
 
+#ifdef CONFIG_LOCK_DOWN_KERNEL
+extern bool __kernel_is_locked_down(const char *what, bool first);
+#else
+static inline bool __kernel_is_locked_down(const char *what, bool first)
+{
+	return false;
+}
+#endif
+
+#define kernel_is_locked_down(what)					\
+	({								\
+		static bool message_given;				\
+		bool locked_down = __kernel_is_locked_down(what, !message_given); \
+		message_given = true;					\
+		locked_down;						\
+	})
+
 /* Internal, do not use. */
 int __must_check _kstrtoul(const char *s, unsigned int base, unsigned long *res);
 int __must_check _kstrtol(const char *s, unsigned int base, long *res);
diff --git a/include/linux/security.h b/include/linux/security.h
index ce6265960d6c..f9a894b42d4c 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1753,5 +1753,13 @@ static inline void free_secdata(void *secdata)
 { }
 #endif /* CONFIG_SECURITY */
 
+#ifdef CONFIG_LOCK_DOWN_KERNEL
+extern void __init init_lockdown(void);
+#else
+static inline void __init init_lockdown(void);
+{
+}
+#endif
+
 #endif /* ! __LINUX_SECURITY_H */
 
diff --git a/security/Kconfig b/security/Kconfig
index e8e449444e65..8e01fd59ae7e 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -205,6 +205,14 @@ config STATIC_USERMODEHELPER_PATH
 	  If you wish for all usermode helper programs to be disabled,
 	  specify an empty string here (i.e. "").
 
+config LOCK_DOWN_KERNEL
+	bool "Allow the kernel to be 'locked down'"
+	help
+	  Allow the kernel to be locked down under certain circumstances, for
+	  instance if UEFI secure boot is enabled.  Locking down the kernel
+	  turns off various features that might otherwise allow access to the
+	  kernel image (eg. setting MSR registers).
+
 source security/selinux/Kconfig
 source security/smack/Kconfig
 source security/tomoyo/Kconfig
diff --git a/security/Makefile b/security/Makefile
index f2d71cdb8e19..8c4a43e3d4e0 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -29,3 +29,6 @@ obj-$(CONFIG_CGROUP_DEVICE)		+= device_cgroup.o
 # Object integrity file lists
 subdir-$(CONFIG_INTEGRITY)		+= integrity
 obj-$(CONFIG_INTEGRITY)			+= integrity/
+
+# Allow the kernel to be locked down
+obj-$(CONFIG_LOCK_DOWN_KERNEL)		+= lock_down.o
diff --git a/security/lock_down.c b/security/lock_down.c
new file mode 100644
index 000000000000..d8595c0e6673
--- /dev/null
+++ b/security/lock_down.c
@@ -0,0 +1,60 @@
+/* Lock down the kernel
+ *
+ * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public Licence
+ * as published by the Free Software Foundation; either version
+ * 2 of the Licence, or (at your option) any later version.
+ */
+
+#include <linux/security.h>
+#include <linux/export.h>
+
+static __ro_after_init bool kernel_locked_down;
+
+/*
+ * Put the kernel into lock-down mode.
+ */
+static void __init lock_kernel_down(const char *where)
+{
+	if (!kernel_locked_down) {
+		kernel_locked_down = true;
+		pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
+			  where);
+	}
+}
+
+static int __init lockdown_param(char *ignored)
+{
+	lock_kernel_down("command line");
+	return 0;
+}
+
+early_param("lockdown", lockdown_param);
+
+/*
+ * Lock the kernel down from very early in the arch setup.  This must happen
+ * prior to things like ACPI being initialised.
+ */
+void __init init_lockdown(void)
+{
+#ifdef CONFIG_LOCK_DOWN_IN_EFI_SECURE_BOOT
+	if (efi_enabled(EFI_SECURE_BOOT))
+		lock_kernel_down("EFI secure boot");
+#endif
+}
+
+/**
+ * kernel_is_locked_down - Find out if the kernel is locked down
+ * @what: Tag to use in notice generated if lockdown is in effect
+ */
+bool __kernel_is_locked_down(const char *what, bool first)
+{
+	if (what && first && kernel_locked_down)
+		pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
+			  what);
+	return kernel_locked_down;
+}
+EXPORT_SYMBOL(__kernel_is_locked_down);