BACKPORT: security: Create "kernel hardening" config area

Right now kernel hardening options are scattered around various Kconfig
files. This can be a central place to collect these kinds of options
going forward. This is initially populated with the memory initialization
options from the gcc-plugins.

The Android backport only adds INIT_STACK_NONE, as GCC plugins are
unavailable in the Android 4.14 tree.

Change-Id: Ic11cb574d2b447e30b0d93977a6707b53744e1cf
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
(cherry picked from commit 9f671e58159adea641f76c56d1f0bbdcb3c524ff)
Bug: 133428616
Signed-off-by: Alexander Potapenko <glider@google.com>

security/Kconfig

@@ -272,5 +272,7 @@ config DEFAULT_SECURITY
 	default "apparmor" if DEFAULT_SECURITY_APPARMOR
 	default "" if DEFAULT_SECURITY_DAC
 
+source "security/Kconfig.hardening"
+
 endmenu
 

security/Kconfig.hardening

@@ -0,0 +1,32 @@
+menu "Kernel hardening options"
+
+menu "Memory initialization"
+
+choice
+	prompt "Initialize kernel stack variables at function entry"
+	default INIT_STACK_NONE
+	help
+	  This option enables initialization of stack variables at
+	  function entry time. This has the possibility to have the
+	  greatest coverage (since all functions can have their
+	  variables initialized), but the performance impact depends
+	  on the function calling complexity of a given workload's
+	  syscalls.
+
+	  This chooses the level of coverage over classes of potentially
+	  uninitialized variables. The selected class will be
+	  initialized before use in a function.
+
+	config INIT_STACK_NONE
+		bool "no automatic initialization (weakest)"
+		help
+		  Disable automatic stack variable initialization.
+		  This leaves the kernel vulnerable to the standard
+		  classes of uninitialized stack variable exploits
+		  and information exposures.
+
+endchoice
+
+endmenu
+
+endmenu