x86/mm/KASLR: Propagate KASLR status to kernel proper

Commit:

  e2b32e678513 ("x86, kaslr: randomize module base load address")

made module base address randomization unconditional and didn't regard
disabled KKASLR due to CONFIG_HIBERNATION and command line option
"nokaslr". For more info see (now reverted) commit:

  f47233c2d34f ("x86/mm/ASLR: Propagate base load address calculation")

In order to propagate KASLR status to kernel proper, we need a single bit
in boot_params.hdr.loadflags and we've chosen bit 1 thus leaving the
top-down allocated bits for bits supposed to be used by the bootloader.

Originally-From: Jiri Kosina <jkosina@suse.cz>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 11 insertions, 13 deletions

diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index d1ac80b72c72..005c03e93fc5 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -33,6 +33,7 @@
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
+#include <asm/setup.h>
 
 #if 0
 #define DEBUGP(fmt, ...)                                \
@@ -47,21 +48,13 @@ do {							\
 
 #ifdef CONFIG_RANDOMIZE_BASE
 static unsigned long module_load_offset;
-static int randomize_modules = 1;
 
 /* Mutex protects the module_load_offset. */
 static DEFINE_MUTEX(module_kaslr_mutex);
 
-static int __init parse_nokaslr(char *p)
-{
-        randomize_modules = 0;
-        return 0;
-}
-early_param("nokaslr", parse_nokaslr);
-
 static unsigned long int get_module_load_offset(void)
 {
-        if (randomize_modules) {
+        if (kaslr_enabled()) {
                 mutex_lock(&module_kaslr_mutex);
                 /*
                  * Calculate the module_load_offset the first time this
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 0a2421cca01f..014466b152b5 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -832,10 +832,15 @@ static void __init trim_low_memory_range(void)
 static int
 dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
 {
-        pr_emerg("Kernel Offset: 0x%lx from 0x%lx "
-                 "(relocation range: 0x%lx-0x%lx)\n",
-                 (unsigned long)&_text - __START_KERNEL, __START_KERNEL,
-                 __START_KERNEL_map, MODULES_VADDR-1);
+        if (kaslr_enabled()) {
+                pr_emerg("Kernel Offset: 0x%lx from 0x%lx (relocation range: 0x%lx-0x%lx)\n",
+                         (unsigned long)&_text - __START_KERNEL,
+                         __START_KERNEL,
+                         __START_KERNEL_map,
+                         MODULES_VADDR-1);
+        } else {
+                pr_emerg("Kernel Offset: disabled\n");
+        }
 
         return 0;
 }