Add the ability to lock down access to the running kernel image

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@redhat.com>
Acked-by: James Morris <james.l.morris@oracle.com>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0001-Add-the-ability-to-lock-down-access-to-the-running-k.patch

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3fd291503576f1407e633851bec2b785152e6576..dcc8916098e77ba2d9e7a0be872abfede146d5de 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -306,6 +306,23 @@ 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 73f1ef625d40c900430778fab29f8bad6cd2e029..2e9690f3d1ceb788a47ccdfef3df1183ac026073 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1801,5 +1801,13 @@ 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 5a9df6d700c7da07df4261e0d23854d9b821efb9..4c15a4a02d3d3ee74b8ed378e66beb629b29aabe 100644 (file)
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -240,6 +240,14 @@ 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 4d2d3782ddefd3fbdd6d2984a1faa8a2bd6561ae..507ac8c520ce531e5d7cc2b89ae0e6ad412747b5 100644 (file)
--- a/security/Makefile
+++ b/security/Makefile
@@ -30,3 +30,6 @@ 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 (file)
index 0000000..d8595c0
--- /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@redhat.com)
+ *
+ * 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);