x86/mm/pti: Introduce pti_finalize()

Introduce a new function to finalize the kernel mappings for the userspace
page-table after all ro/nx protections have been applied to the kernel
mappings.

Also move the call to pti_clone_kernel_text() to that function so that it
will run on 32 bit kernels too.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Pavel Machek <pavel@ucw.cz>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: linux-mm@kvack.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Waiman Long <llong@redhat.com>
Cc: "David H . Gutteridge" <dhgutteridge@sympatico.ca>
Cc: joro@8bytes.org
Link: https://lkml.kernel.org/r/1531906876-13451-30-git-send-email-joro@8bytes.org

arch/x86/include/asm/pti.h

@@ -6,10 +6,9 @@
 #ifdef CONFIG_PAGE_TABLE_ISOLATION
 extern void pti_init(void);
 extern void pti_check_boottime_disable(void);
-extern void pti_clone_kernel_text(void);
+extern void pti_finalize(void);
 #else
 static inline void pti_check_boottime_disable(void) { }
-static inline void pti_clone_kernel_text(void) { }
 #endif
 
 #endif /* __ASSEMBLY__ */

arch/x86/mm/init_64.c

@@ -1291,12 +1291,6 @@ void mark_rodata_ro(void)
 			(unsigned long) __va(__pa_symbol(_sdata)));
 
 	debug_checkwx();
-
-	/*
-	 * Do this after all of the manipulation of the
-	 * kernel text page tables are complete.
-	 */
-	pti_clone_kernel_text();
 }
 
 int kern_addr_valid(unsigned long addr)

arch/x86/mm/pti.c

@@ -462,7 +462,7 @@ static inline bool pti_kernel_image_global_ok(void)
  * For some configurations, map all of kernel text into the user page
  * tables.  This reduces TLB misses, especially on non-PCID systems.
  */
-void pti_clone_kernel_text(void)
+static void pti_clone_kernel_text(void)
 {
 	/*
 	 * rodata is part of the kernel image and is normally
@@ -526,3 +526,15 @@ void __init pti_init(void)
 	pti_setup_espfix64();
 	pti_setup_vsyscall();
 }
+
+/*
+ * Finalize the kernel mappings in the userspace page-table.
+ */
+void pti_finalize(void)
+{
+	/*
+	 * Do this after all of the manipulation of the
+	 * kernel text page tables are complete.
+	 */
+	pti_clone_kernel_text();
+}

include/linux/pti.h

@@ -6,6 +6,7 @@
 #include <asm/pti.h>
 #else
 static inline void pti_init(void) { }
+static inline void pti_finalize(void) { }
 #endif
 
 #endif

init/main.c

@@ -1065,6 +1065,13 @@ static int __ref kernel_init(void *unused)
 	jump_label_invalidate_initmem();
 	free_initmem();
 	mark_readonly();
+
+	/*
+	 * Kernel mappings are now finalized - update the userspace page-table
+	 * to finalize PTI.
+	 */
+	pti_finalize();
+
 	system_state = SYSTEM_RUNNING;
 	numa_default_policy();