x86/KASLR: Initialize mapping_info every time

As it turns out, mapping_info DOES need to be initialized every
time, because pgt_data address could be changed during kernel
relocation. So it can not be build time assigned.

Without this, page tables were not being corrected updated, which
could cause reboots when a physical address beyond 2G was chosen.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: kernel-hardening@lists.openwall.com
Cc: lasse.collin@tukaani.org
Link: http://lkml.kernel.org/r/1462825332-10505-2-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/boot/compressed/pagetable.c

@@ -89,17 +89,6 @@ static void prepare_level4(void)
 	}
 }
 
-/*
- * Mapping information structure passed to kernel_ident_mapping_init().
- * Since this never changes, there's no reason to repeatedly fill it
- * in on the stack when calling add_identity_map().
- */
-static struct x86_mapping_info mapping_info = {
-	.alloc_pgt_page	= alloc_pgt_page,
-	.context	= &pgt_data,
-	.pmd_flag	= __PAGE_KERNEL_LARGE_EXEC,
-};
-
 /*
  * Adds the specified range to what will become the new identity mappings.
  * Once all ranges have been added, the new mapping is activated by calling
@@ -107,6 +96,11 @@ static struct x86_mapping_info mapping_info = {
  */
 void add_identity_map(unsigned long start, unsigned long size)
 {
+	struct x86_mapping_info mapping_info = {
+		.alloc_pgt_page	= alloc_pgt_page,
+		.context	= &pgt_data,
+		.pmd_flag	= __PAGE_KERNEL_LARGE_EXEC,
+	};
 	unsigned long end = start + size;
 
 	/* Make sure we have a top level page table ready to use. */