From d261a0f15a350d81430d3937d3c02118c395d27c Mon Sep 17 00:00:00 2001
From: Dennis Kobert <dennis@kobert.dev>
Date: Fri, 8 Nov 2019 07:28:08 +0100
Subject: Implement guarding page

---
 kernel/run                          |  4 ++--
 kernel/src/boot.asm                 | 33 +++++++++++++++++++++++----------
 kernel/src/interrupts/exceptions.rs | 35 ++++++++++++++++++++++++++++++++++-
 kernel/src/interrupts/table.rs      |  4 ++++
 kernel/src/lib.rs                   |  2 +-
 kernel/src/linker.ld                |  8 ++++++++
 6 files changed, 72 insertions(+), 14 deletions(-)

diff --git a/kernel/run b/kernel/run
index c18450b..1353d92 100755
--- a/kernel/run
+++ b/kernel/run
@@ -8,7 +8,7 @@ onerr() {
 trap onerr ERR
 
 name="uff"
-build_mode=debug
+build_mode=release
 action=help
 target=x86_64
 test_mode=false
@@ -80,7 +80,7 @@ build() {
     #    cargo xbuild
     #fi
     if ! $test_mode; then
-        cargo xbuild
+        cargo xbuild "--$build_mode"
     fi
     build_iso
 }
diff --git a/kernel/src/boot.asm b/kernel/src/boot.asm
index 95b699a..1c0b3da 100644
--- a/kernel/src/boot.asm
+++ b/kernel/src/boot.asm
@@ -5,14 +5,16 @@ section .text
 bits 32
 start:
 	mov esp, stack_top
-
+    
 	call check_multiboot
 	call check_cpuid
 	call check_long_mode
 
 	call setup_page_tables
 	call enable_paging
-	; load the 64-bit GDT
+    
+	
+    ; load the 64-bit GDT
     lgdt [gdt64.pointer]
 	jmp gdt64.code:long_mode_start
 
@@ -96,21 +98,27 @@ setup_page_tables:
 
 .map_p2_table:
     ; map ecx-th P2 entry to a huge page that starts at address 2MiB*ecx
+    mov ebx, eax
+    cmp eax, stack_bottom + 0b10000011 - 0x400000 
+    jne .hit_stack 
+    and ebx, ~1
     mov [p2_table + ecx     ], eax ; map ecx-th entry
-    add eax, 0x200000  ; 2MiB
-    mov [p2_table + ecx + 8 ], eax ; map ecx-th entry
-    add eax, 0x200000  ; 2MiB
-    mov [p2_table + ecx + 16], eax ; map ecx-th entry
-    add eax, 0x200000  ; 2MiB
-    mov [p2_table + ecx + 24], eax ; map ecx-th entry
+	add ecx, 8
+
+.hit_stack:
+    mov [p2_table + ecx     ], ebx ; map ecx-th entry
     add eax, 0x200000  ; 2MiB
 
-	add ecx, 32
+	add ecx, 8
+	;add ecx, 32
     cmp ecx, 4096      ; if counter == 512, the whole P2 table is mapped
     jne .map_p2_table  ; else map the next entry
 
 	ret
 
+    
+    
+
 enable_paging:
 	mov eax, p4_table
 	mov cr3, eax
@@ -131,6 +139,10 @@ enable_paging:
     or eax, 1 << 31
     mov cr0, eax
 
+    ; move stack pointer to accommodate for the guard page
+    add esp, 0x200000
+
+
     ret
 
 section .rodata
@@ -159,6 +171,7 @@ p3_table:
 	resb 4096
 p2_table:
 	resb 4096
+alignb 4096 * 512
 stack_bottom:
-	resb 4096 * 8
+	resb 4096 * 4
 stack_top:
diff --git a/kernel/src/interrupts/exceptions.rs b/kernel/src/interrupts/exceptions.rs
index 5ec7588..08555c4 100644
--- a/kernel/src/interrupts/exceptions.rs
+++ b/kernel/src/interrupts/exceptions.rs
@@ -1,7 +1,40 @@
 use crate::io::vga_text::OStream;
-use x86_64::structures::idt::InterruptStackFrame;
+use x86_64::structures::idt::{InterruptStackFrame, PageFaultErrorCode};
 
 pub extern "x86-interrupt" fn breakpoint_handler(stack_frame: &mut InterruptStackFrame) {
     let mut stdout = OStream::new();
     stdout.print(b"EXCEPTION: BREAKPOINT\n");
 }
+
+pub extern "x86-interrupt" fn page_fault_handler(
+    stack_frame: &mut InterruptStackFrame,
+    error_code: PageFaultErrorCode,
+) {
+    use x86_64::registers::control::Cr2;
+
+    let mut stdout = OStream::new();
+    stdout.print(b"EXCEPTION: PAGEFAULT\n");
+    loop {}
+    panic!("PAGE FAULT");
+    //println!("Accessed Address: {:?}", Cr2::read());
+    //println!("Error Code: {:?}", error_code);
+    //println!("{:#?}", stack_frame);
+}
+
+pub extern "x86-interrupt" fn segment_not_present_handler(
+    stack_frame: &mut InterruptStackFrame,
+    error_code: u64,
+) {
+    loop {}
+    let mut stdout = OStream::new();
+    stdout.print(b"EXCEPTION: SEGMENT NOT PRESENT\n");
+}
+
+extern "x86-interrupt" fn double_fault_handler(
+    stack_frame: &mut InterruptStackFrame,
+    _error_code: u64,
+) {
+    let mut stdout = OStream::new();
+    stdout.print(b"EXCEPTION: DOUBLE FAULT");
+    loop {}
+}
diff --git a/kernel/src/interrupts/table.rs b/kernel/src/interrupts/table.rs
index 47d6ead..6472014 100644
--- a/kernel/src/interrupts/table.rs
+++ b/kernel/src/interrupts/table.rs
@@ -7,6 +7,10 @@ lazy_static! {
         let mut idt = InterruptDescriptorTable::new();
         idt.breakpoint
             .set_handler_fn(super::exceptions::breakpoint_handler);
+        idt.page_fault
+            .set_handler_fn(super::exceptions::page_fault_handler);
+        idt.segment_not_present
+            .set_handler_fn(super::exceptions::segment_not_present_handler);
         idt
     };
 }
diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index 45ba8e1..b36d731 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -39,6 +39,7 @@ pub extern "C" fn _start() -> ! {
     core::iter::successors(Some(0), |n| Some(n + 1))
         .for_each(|n| write!(&mut stdout, "hello world {}!", n).unwrap());
 
+    x86_64::instructions::interrupts::int3();
     loop {}
 }
 
@@ -72,6 +73,5 @@ pub extern "C" fn panic_handler(_info: &core::panic::PanicInfo) -> ! {
         write!(serial::SerialStream::new(), "Testing failed\n").unwrap();
         qemu::exit_qemu(qemu::QemuExitCode::Failed);
     }
-    x86_64::instructions::interrupts::int3();
     loop {}
 }
diff --git a/kernel/src/linker.ld b/kernel/src/linker.ld
index 9b5355c..d187fd2 100644
--- a/kernel/src/linker.ld
+++ b/kernel/src/linker.ld
@@ -13,4 +13,12 @@ SECTIONS {
     {
         *(.text)
     }
+    rodata : 
+    {
+        *(.rodata)
+    }
+    .bss :
+    {
+        *(.bss)
+    }
 }
-- 
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