From 5ff8596233e5946013d15b29c3779e4531fcc779 Mon Sep 17 00:00:00 2001
From: Julien CLEMENT <julien.clement@epita.fr>
Date: Wed, 8 Dec 2021 16:20:38 +0100
Subject: [PATCH] feat(paging): map kernel using elf section flags

Signed-off-by: Julien CLEMENT <julien.clement@epita.fr>
---
 src/lib.rs               | 17 ++++++++++++++---
 src/memory/paging/mod.rs | 28 +++++++++++++++++++++++-----
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 2e47eca..5e9eacd 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,6 +12,8 @@ extern crate multiboot2;
 
 use core::panic::PanicInfo;
 use vga::{Color, ColorCode};
+use memory::paging::{Size4KiB, FrameAllocator};
+use multiboot2::BootInformation;
 
 #[panic_handler]
 fn panic_handler(info: &PanicInfo) -> ! {
@@ -26,14 +28,24 @@ pub fn hlt_loop() -> ! {
     }
 }
 
-pub fn init() {
+pub fn init<A>(frame_allocator: &mut A, boot_info: &BootInformation)
+    where A: FrameAllocator<Size4KiB>
+{
     vga::change_color(ColorCode::new(Color::LightCyan, Color::Black));
     println!("Starting init");
+    enable_nxe_bit();
+    memory::kernel_remap(frame_allocator, boot_info);
     gdt::init_gdt();
     interrupts::init_idt();
     vga::change_color(ColorCode::new(Color::LightGreen, Color::Black));
 }
 
+fn enable_nxe_bit() {
+    println!("Enabling nxe bit");
+    use x86_64::registers::control::{Efer, EferFlags};
+    unsafe { Efer::update(|efer| *efer |= EferFlags::NO_EXECUTE_ENABLE) }
+}
+
 fn get_frame_allocator(multiboot_info_addr: usize) -> memory::AreaFrameAllocator {
     let boot_info = unsafe { multiboot2::load(multiboot_info_addr) };
     let memory_map_tag = boot_info.memory_map_tag().expect("Memory map tag required");
@@ -62,9 +74,8 @@ pub extern "C" fn julios_main(multiboot_info_addr: usize) -> ! {
 
     let mut frame_allocator = get_frame_allocator(multiboot_info_addr);
 
-    memory::kernel_remap(&mut frame_allocator, boot_info);
 
-    init();
+    init(&mut frame_allocator, &boot_info);
     println!("***JuliOS V0.1.0***");
     serial_println!("Hello serial");
     memory::paging::test_paging(&mut frame_allocator);
diff --git a/src/memory/paging/mod.rs b/src/memory/paging/mod.rs
index 2b5d9d5..835fc12 100644
--- a/src/memory/paging/mod.rs
+++ b/src/memory/paging/mod.rs
@@ -1,4 +1,4 @@
-use multiboot2::BootInformation;
+use multiboot2::{BootInformation, ElfSection};
 pub use x86_64::structures::paging::{FrameAllocator, Size4KiB, PageTable, RecursivePageTable, Page, PageTableFlags as Flags, Mapper, PhysFrame as Frame};
 use crate::println;
 use x86_64::{VirtAddr, PhysAddr};
@@ -10,9 +10,29 @@ mod temporary_page;
 
 pub const P4: *mut PageTable = 0o177777_777_777_777_777_0000 as *mut _;
 
+fn get_flags_from_elf_section(section: &ElfSection) -> Flags {
+    use multiboot2::{ELF_SECTION_ALLOCATED, ELF_SECTION_WRITABLE,
+        ELF_SECTION_EXECUTABLE};
+
+    let mut flags = Flags::empty();
+
+    if section.flags().contains(ELF_SECTION_ALLOCATED) {
+        flags = flags | Flags::PRESENT;
+    }
+    if section.flags().contains(ELF_SECTION_WRITABLE) {
+        flags = flags | Flags::WRITABLE;
+    }
+    if !section.flags().contains(ELF_SECTION_EXECUTABLE) {
+        flags = flags | Flags::NO_EXECUTE;
+    }
+
+    flags
+}
+
 pub fn kernel_remap<A>(allocator: &mut A, boot_info: &BootInformation)
     where A: FrameAllocator<Size4KiB>
 {
+    println!("Remapping kernel");
     let mut temporary_page = TemporaryPage::new(Page::containing_address(VirtAddr::new(0xcafebabe)), allocator);
     let mut active_table = get_active_page_table();
     let mut new_table = {
@@ -33,7 +53,7 @@ pub fn kernel_remap<A>(allocator: &mut A, boot_info: &BootInformation)
                     "sections need to be page aligned");
 
 
-            let flags = Flags::WRITABLE | Flags::PRESENT;
+            let flags = get_flags_from_elf_section(section);
 
             let start_frame = Frame::<Size4KiB>::containing_address(PhysAddr::new(section.start_address() as u64));
             let end_frame = Frame::containing_address(PhysAddr::new(section.end_address() as u64 - 1));
@@ -129,7 +149,5 @@ pub fn test_paging<A>(allocator: &mut A)
     let page_ptr: *mut u8 = page.start_address().as_mut_ptr();
     let frame_ptr: *mut u8 = frame.start_address().as_u64() as *mut u8;
 
-    unsafe {
-        println!("Page: {:#?}, Frame: {:#?}", page_ptr, frame_ptr);
-    }
+    println!("Page: {:#?}, Frame: {:#?}", page_ptr, frame_ptr);
 }