x86, kaslr: boot-time selectable with hibernation

Changes kASLR from being compile-time selectable (blocked by
CONFIG_HIBERNATION), to being boot-time selectable (with hibernation
available by default) via the "kaslr" kernel command line.

Signed-off-by: Kees Cook <[e-mail]>
Acked-by: Pavel Machek <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/kernel-parameters.txt

···
 	js=		[HW,JOY] Analog joystick
 			See Documentation/input/joystick.txt.
 
+	kaslr/nokaslr	[X86]
+			Enable/disable kernel and module base offset ASLR
+			(Address Space Layout Randomization) if built into
+			the kernel. When CONFIG_HIBERNATION is selected,
+			kASLR is disabled by default. When kASLR is enabled,
+			hibernation will be disabled.
+
 	keepinitrd	[HW,ARM]
 
 	kernelcore=nn[KMG]	[KNL,X86,IA-64,PPC] This parameter
···
 
 	noapic		[SMP,APIC] Tells the kernel to not make use of any
 			IOAPICs that may be present in the system.
-
-	nokaslr		[X86]
-			Disable kernel and module base offset ASLR (Address
-			Space Layout Randomization) if built into the kernel.
 
 	noautogroup	Disable scheduler automatic task group creation.
 

arch/x86/Kconfig

···
 config RANDOMIZE_BASE
 	bool "Randomize the address of the kernel image"
 	depends on RELOCATABLE
-	depends on !HIBERNATION
 	default n
 	---help---
 	   Randomizes the physical and virtual address at which the

arch/x86/boot/compressed/aslr.c

···
 	unsigned long choice = (unsigned long)output;
 	unsigned long random;
 
-	if (cmdline_find_option_bool("nokaslr")) {
-		debug_putstr("KASLR disabled...\n");
+#ifdef CONFIG_HIBERNATION
+	if (!cmdline_find_option_bool("kaslr")) {
+		debug_putstr("KASLR disabled by default...\n");
 		goto out;
 	}
+#else
+	if (cmdline_find_option_bool("nokaslr")) {
+		debug_putstr("KASLR disabled by cmdline...\n");
+		goto out;
+	}
+#endif
 
 	/* Record the various known unsafe memory ranges. */
 	mem_avoid_init((unsigned long)input, input_size,

kernel/power/hibernate.c

···
 	return 1;
 }
 
+static int __init kaslr_nohibernate_setup(char *str)
+{
+	return nohibernate_setup(str);
+}
+
 __setup("noresume", noresume_setup);
 __setup("resume_offset=", resume_offset_setup);
 __setup("resume=", resume_setup);
···
 __setup("resumewait", resumewait_setup);
 __setup("resumedelay=", resumedelay_setup);
 __setup("nohibernate", nohibernate_setup);
+__setup("kaslr", kaslr_nohibernate_setup);