From 0c0d220d3eaf61d6ab0aca6d006c278edc5a0440 Mon Sep 17 00:00:00 2001
From: Aqua-sama <aqua@iserlohn-fortress.net>
Date: Mon, 15 Mar 2021 22:41:31 +0200
Subject: Map .text and .rodata as read-only

---
 linker.ld  |  4 +---
 src/boot.S | 55 +++++++++++++++++++++++++++----------------------------
 2 files changed, 28 insertions(+), 31 deletions(-)

diff --git a/linker.ld b/linker.ld
index 764b78b..d1dedd2 100644
--- a/linker.ld
+++ b/linker.ld
@@ -16,7 +16,6 @@ SECTIONS
 
     /* Begin putting sections at 4 MiB */
     . = VADDR_BASE;
-    _kernel_start = .;
 
     .text ALIGN(4K) : AT(ADDR(.text) - VADDR_BASE + 4M) {
         begin_text = .;
@@ -34,6 +33,7 @@ SECTIONS
  
     /* Read-write data (initialized) */
     .data ALIGN(4K) : AT(ADDR(.data) - VADDR_BASE + 4M) {
+        begin_data = .;
         begin_constinit = .;
         *(.constinit)
         end_constinit = .;
@@ -42,7 +42,6 @@ SECTIONS
         KEEP(*(.init_array));   /* global constructors */
         end_ctors = .;
 
-        begin_data = .;
         *(.data)
         end_data = .;
     }
@@ -55,5 +54,4 @@ SECTIONS
         *(.stack)
         end_bss = .;
     }
-    _kernel_end = .;
 }
diff --git a/src/boot.S b/src/boot.S
index e39883e..0451066 100644
--- a/src/boot.S
+++ b/src/boot.S
@@ -52,7 +52,24 @@ kernel_ptable0:
  */
 .section .multiboot.text, "ax"
 .global VADDR_OFFSET
-.set VADDR_OFFSET, 0xc0000000 - 0x400000
+    .set VADDR_OFFSET, 0xc0000000 - 0x400000
+
+.macro map begin, end, access
+    mov $\begin - VADDR_OFFSET, %esi
+1:
+    cmpl $(\end - VADDR_OFFSET), %esi
+    jge 2f              # move to next section
+
+    movl %esi, %edx     # map physical address
+    orl $\access, %edx  # access bits
+    movl %edx, (%edi)
+
+    addl $4096, %esi    # Size of page is 4096 bytes.
+    addl $4, %edi       # Size of entries in kernel_ptable0 is 4 bytes.
+    loop 1b             # Loop to the next entry if we haven't finished.
+2:
+.endm
+
 .global _start
     .type _start, @function
 _start:
@@ -60,37 +77,19 @@ _start:
 
     # Physical address of kernel_ptable0.
     movl $(kernel_ptable0 - VADDR_OFFSET), %edi
-
-    # Only map the kernel.
-    mov $_kernel_start - VADDR_OFFSET, %esi
     # Map 1024 pages
     movl $1024, %ecx
 
-l_page_init:
-    cmpl $(_kernel_end - VADDR_OFFSET), %esi
-    jge map_table
+    map begin_text, end_text, 0x001
+    map begin_rodata, end_rodata, 0x001
+    map begin_data, end_data, 0x003
+    map begin_bss, end_bss, 0x003
 
-    /* TODO: Map physical address as "present, writable". Note that this maps .text and .rodata as writable.
-             Mind security and map them as non-writable. */
-	movl %esi, %edx
-	orl $0x003, %edx
-	movl %edx, (%edi)
-
-	# Size of page is 4096 bytes.
-	addl $4096, %esi
-	# Size of entries in kernel_ptable0 is 4 bytes.
-	addl $4, %edi
-	# Loop to the next entry if we haven't finished.
-	loop l_page_init
-
-map_table:
-/*
-    Enabling paging does not change the next instruction, which continues to be physical. Therefore, map the kernel
-    to both its physical address and to the higher half.
-    Use the page table at:
-      - entry   1       starts 0x0040 0000      ends 0x007f ffff
-      - entry 768       starts 0xc000 0000      ends 0xc03f ffff
- */
+    # Enabling paging does not change the next instruction, which continues to be physical. Therefore, map the kernel
+    # to both its physical address and to the higher half.
+    # Use the page table at:
+    #   - entry   1       starts 0x0040 0000      ends 0x007f ffff
+    #   - entry 768       starts 0xc000 0000      ends 0xc03f ffff
     movl $(kernel_ptable0 - VADDR_OFFSET + 0x003), kernel_pagedir - VADDR_OFFSET + 1 * 4
     movl $(kernel_ptable0 - VADDR_OFFSET + 0x003), kernel_pagedir - VADDR_OFFSET + 768 * 4
 
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