x86_64: pmap: enable kernel-mode write-protection

arch/x86_64/include/arch/paging.h

@@ -1,8 +1,8 @@
 #ifndef ARCH_PAGING_H_
 #define ARCH_PAGING_H_
 
-#include <kernel/types.h>
 #include <kernel/compiler.h>
+#include <kernel/types.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -55,6 +55,7 @@ enum page_size {
    defined in pmap_ctrl.S */
 extern int gigabyte_pages(void);
 extern int enable_nx(void);
+extern int enable_wp(void);
 
 #ifdef __cplusplus
 }

arch/x86_64/pmap.c

@@ -351,6 +351,8 @@ void pmap_bootstrap(void)
 	       can_use_gbpages == 1 ? "en" : "dis");
 	enable_nx();
 	printk("pmap: NX protection enabled");
+	enable_wp();
+	printk("pmap: kernel-mode write protection enabled");
 
 	enum page_size hugepage = PS_2M;
 	if (can_use_gbpages) {

arch/x86_64/pmap_ctrl.S

@@ -30,6 +30,7 @@ gigabyte_pages:
 	pop %rbp
 	ret
 
+
 	.global enable_nx
 	.type enable_nx, @function
 
@@ -40,3 +41,14 @@ enable_nx:
 	wrmsr
 
 	ret
+
+
+	.global enable_wp
+	.type enable_wp, @function
+
+enable_wp:
+	mov %cr0, %rax
+	or $0x10000, %rax
+	mov %rax, %cr0
+
+	ret