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fix paging bugs in writeprotection

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This commit is contained in:
Christoph Urlacher
2022-07-04 16:04:55 +02:00
parent 2c8a7524b9
commit 586fe3bb80
3 changed files with 38 additions and 10 deletions
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10
c_os/kernel/Paging.cc
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@ -92,7 +92,7 @@ unsigned int* pg_alloc_page() {
// pruefe ob Page frei
if (((*p_page) & PAGE_RESERVED) == 0) {
*p_page = (*p_page | PAGE_RESERVED);
return (unsigned int*)(i << 12);
return (unsigned int*)(i << 12); // Address without flags (Offset 0)
}
}
return 0;
@ -108,8 +108,10 @@ void pg_write_protect_page(unsigned int* p_page) {
/* hier muss Code eingefügt werden */
unsigned int* page = (unsigned int*)PAGE_TABLE + ((unsigned int)p_page >> 12); // Pagetable entry
unsigned int mask = PAGE_WRITEABLE; // fill to 32bit
*p_page = *p_page & ~mask; // set writable to 0
*page = *page & ~mask; // set writable to 0
}
/*****************************************************************************
@ -121,8 +123,10 @@ void pg_notpresent_page(unsigned int* p_page) {
/* hier muss Code eingefügt werden */
unsigned int* page = (unsigned int*)PAGE_TABLE + ((unsigned int)p_page >> 12); // Pagetable entry
unsigned int mask = PAGE_PRESENT;
*p_page = *p_page & ~mask; // set present to 0
*page = *page & ~mask; // set present to 0
}
/*****************************************************************************

22
c_os/kernel/Paging.h
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@ -52,6 +52,28 @@
#ifndef __Paging_include__
#define __Paging_include__
// Bits fuer Eintraege in der Page-Table
#define PAGE_PRESENT 0x001
#define PAGE_WRITEABLE 0x002
#define PAGE_BIGSIZE 0x080
#define PAGE_RESERVED 0x800 // Bit 11 ist frei fuer das OS
// Adresse des Page-Directory (benoetigt 4 KB)
#define PAGE_DIRECTORY 0x200000
// Adresse der Page-Table (benoetigt 4 KB)
#define PAGE_TABLE 0x201000
// Start- und End-Adresse der 4 KB Seiten die durch die Page-Table adressiert werden
#define FST_ALLOCABLE_PAGE 0x202000
#define LST_ALLOCABLE_PAGE 0x2FF000
// Externe Funktionen in startup.asm
extern "C" {
void paging_on(unsigned int* p_pdir); // Paging einschalten
void invalidate_tlb_entry(unsigned int* ptr); // Page in TLB invalid.
}
// ativiert paging
extern void pg_init();

16
c_os/main.cc
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@ -56,27 +56,29 @@ int main() {
pg_init();
// Trigger Bluescreen
// kout << "Trigger Bluescreen, if you can read this it didn't work" << endl;
kout << "Trigger Bluescreen, if you can read this it didn't work" << endl;
// BlueScreen 1
// asm("int $3");
// BlueScreen 2
// unsigned int* page = pg_alloc_page();
// *page = 42; // Should work
// pg_write_protect_page(page);
// *page = 42; // should trigger BlueScreen
unsigned int* page = pg_alloc_page();
*page = 42;
pg_write_protect_page(page);
invalidate_tlb_entry(page); // If we don't invalidate after first access the write protection
// won't work as no lookup is performed (address in tlb)
*page = 42; // We map logical to physical 1:1 so no need to do any lookup
// If tlb is invalidated this access produces a pagefault
// Demo threads anlegen
// scheduler.ready(new HelloWorldThread());
scheduler.ready(new CoopThreadDemo());
// scheduler.ready(new CoopThreadDemo());
// scheduler.ready(new VBEdemo()); // Switch to VESA graphics mode
// Scheduler starten (schedule() erzeugt den Idle-Thread)
scheduler.schedule();
// TODO: Use templates for queue so threads don't have to be casted down from chain
// TODO: Move scrollback control to thread
// Scheduler doesn't return
return 0;