From 0b22410c5ef3350070aea10789a6b0b84ffef8ef Mon Sep 17 00:00:00 2001
From: Erin <erin@hashbang.sh>
Date: Mon, 5 Jun 2017 11:17:49 -0500
Subject: [PATCH] kernel_main: enable NXE, WRPROT bits before remapping kernel

---
 src/arch/x86_64/mod.rs | 17 +++++++++++++++++
 src/lib.rs             |  6 ++++++
 2 files changed, 23 insertions(+)

diff --git a/src/arch/x86_64/mod.rs b/src/arch/x86_64/mod.rs
index 80f2bd6..36def08 100644
--- a/src/arch/x86_64/mod.rs
+++ b/src/arch/x86_64/mod.rs
@@ -1,2 +1,19 @@
 pub mod device;
 pub mod memory;
+
+pub fn enable_nxe_bit() {
+    use x86::shared::msr;
+
+    const NXE_BIT: u64 = 1<<11;
+    unsafe {
+        let efer = msr::rdmsr(msr::IA32_EFER);
+        msr::wrmsr(msr::IA32_EFER, efer | NXE_BIT)
+    }
+}
+
+pub fn enable_wrprot_bit() {
+    use x86::shared::control_regs::{cr0, cr0_write, CR0_WRITE_PROTECT};
+    unsafe {
+        cr0_write(cr0() | CR0_WRITE_PROTECT);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 57b4010..d3134d2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -20,6 +20,7 @@ mod misc;
 mod logger;
 mod arch;
 
+use arch::x86_64;
 use arch::x86_64::device::vga_console;
 use arch::x86_64::memory;
 use arch::x86_64::memory::FrameAllocator;
@@ -65,6 +66,11 @@ pub extern fn kernel_main(multiboot_info_pointer: usize) {
 
     println!("multiboot start: {:#x}, multiboot end: {:#x}",
         multiboot_start, multiboot_end);
+
+    // Enable required CPU features
+    x86_64::enable_nxe_bit(); // Enable NO_EXECUTE pages
+    x86_64::enable_wrprot_bit(); // Disable writing to non-WRITABLE pages
+
     memory::remap_kernel(&mut frame_allocator, boot_info);
 
     println!("-- remap_kernel finished! --");