From f13b26eeb4f9afba3a1aed2516655b34139979aa Mon Sep 17 00:00:00 2001
From: Loic Guegan <manzerbredes@mailbox.org>
Date: Tue, 27 Apr 2021 19:02:17 +0200
Subject: Making kernel Higher-Half

---
 src/core/paging.cc | 62 +++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 40 insertions(+), 22 deletions(-)

(limited to 'src/core/paging.cc')

diff --git a/src/core/paging.cc b/src/core/paging.cc
index 8e58511..73a5c63 100644
--- a/src/core/paging.cc
+++ b/src/core/paging.cc
@@ -4,29 +4,50 @@
 #include "libs/string.hpp"
 
 char paging_status[PAGING_MAX_PAGE / 8];
-u64* kpml4;
+u64 kernel_vma,stack_pma,userspace_pma;
+u64 kpages[MAX_TABLES][512] __attribute__((aligned(4096)));
+int kpages_next=1; // First page is for the pml4
+
+u64* paging_allocate_table(){
+    u64 addr=(u64)kpages[kpages_next];
+    u64* allocated=(u64*)(addr-kernel_vma);
+    kpages_next++;
+    return allocated;
+}
 
 void paging_enable() {
+    // Init linker variables
+    asm("movq $__kernel_vma, %0":"=r"(kernel_vma));
+    asm("movq $__userspace_pma, %0":"=r"(userspace_pma));
+    asm("movq $__stack_pma, %0":"=r"(stack_pma));
+
     // Init status
     for (int i = 0; i < PAGING_MAX_PAGE / 8; i++) {
         paging_status[i] = 0;
     }
 
+    // Init tables
+    for(int i=0;i<MAX_TABLES;i++){
+        memset(kpages[i], 0, 512*64);
+    }
+ 
     // Allocate paging for the kernel (to not override the source
     // code during the next paging_allocate_table() calls)
-    paging_allocate_contiguous(PAGING_KERNEL_USED_PAGE);
+    paging_allocate_contiguous(userspace_pma/4096);
 
     // Setting up new kernel address space
-    kpml4=paging_allocate_table();
-    for(int i=0;i<PAGING_KERNEL_SPACE_MAX_PAGE;i++){
-        int addr=i*4096;
-        paging_allocate_addr(kpml4,addr,addr, PAGING_OPT_P|PAGING_OPT_RW); // Identity map
+    for(u64 i=0;i<=0x10000000;i+=4096){
+        paging_allocate_addr(kpages[0],kernel_vma+i,i, 0x3,0); // Identity map
     }
+    // 4096 bytes stack
+    paging_allocate_addr(kpages[0],kernel_vma-4096,stack_pma,0x3,0);
+
     // Load new pml4
+    u64 kpage_phy=((u64)kpages[0]-kernel_vma);
     asm volatile(
-        "movq %0, %%rax        \n\t"
-        "movq %%rax, %%cr3     \n\t"
-        :: "r" (kpml4));
+        "mov %0, %%rax        \n\t"
+        "mov %%rax, %%cr3     \n\t"
+        :: "r" (kpage_phy));
 }
 
 u64 paging_as_phy(u64* pml4_table, u64 virt){
@@ -40,6 +61,7 @@ u64 paging_as_phy(u64* pml4_table, u64 virt){
     u64* pt_table=(u64*)PAGE(pd_table[pd]);
     return((PAGE(pt_table[pt]))|(virt&0xFFF));
 }
+
 u64* paging_allocate_contiguous(int npages){
     int n_contiguous=0;
     for (int i = 0; i < PAGING_MAX_PAGE / 8; i++) {
@@ -116,12 +138,6 @@ void paging_dump(int min, int max) {
     }
 }
 
-u64* paging_allocate_table(){
-    u64* table=paging_allocate_contiguous(8);
-    memset(table, 0, 32768); // nb_entries * entry size = 512 * 64
-    return table;
-}
-
 void paging_deallocate_table(u64* table){
     char *c_table=(char*)PAGE((u64)table);
     for(u8 i=0;i<8;i++){
@@ -130,7 +146,7 @@ void paging_deallocate_table(u64* table){
     }
 }
 
-void paging_allocate_addr(u64* pml4_table, u64 virt, u64 phy, u16 options){
+void paging_allocate_addr(u64* pml4_table, u64 virt, u64 phy, u16 options, u64 offset){
     u16 pml4=virt>>39&0x1FF;
     u16 pdp=virt>>30&0x1FF;
     u16 pd=virt>>21&0x1FF;
@@ -141,27 +157,29 @@ void paging_allocate_addr(u64* pml4_table, u64 virt, u64 phy, u16 options){
     if(pml4_table[pml4] == 0){
         pml4_table[pml4]=(u64)paging_allocate_table();
         pml4_table[pml4]|=options;
-        paging_allocate_addr(pml4_table,virt,phy,options);
+        paging_allocate_addr(pml4_table,virt,phy,options,offset);
         return;
     }
+
     // Solve pd
-    u64* pdp_table=(u64*)PAGE(pml4_table[pml4]);
+    u64* pdp_table=(u64*)(PAGE(pml4_table[pml4])+offset);
     if(pdp_table[pdp] == 0){
         pdp_table[pdp]=(u64)paging_allocate_table();
         pdp_table[pdp]|=options;
-        paging_allocate_addr(pml4_table,virt,phy,options);
+        paging_allocate_addr(pml4_table,virt,phy,options,offset);
         return;
     }
+    
     // Solve pt
-    u64* pd_table=(u64*)PAGE(pdp_table[pdp]);
+    u64* pd_table=(u64*)(PAGE(pdp_table[pdp])+offset);
     if(pd_table[pd] == 0){
         pd_table[pd]=(u64)paging_allocate_table();
         pd_table[pd]|=options;
-        paging_allocate_addr(pml4_table,virt,phy,options);
+        paging_allocate_addr(pml4_table,virt,phy,options,offset);
         return;
     }
     // Solve address
-    u64* pt_table=(u64*)PAGE(pd_table[pd]);
+    u64* pt_table=(u64*)(PAGE(pd_table[pd])+offset);
     if(pt_table[pt] == 0){
         pt_table[pt]=PAGE(phy);
         pt_table[pt]|=options;
-- 
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