added magic value to attempt to deal with potential double freesHEADmaster

2 files changed, 16 insertions, 1 deletions

diff --git a/kernel/kernel.cpp b/kernel/kernel.cpp
index 3801082..1ac9d45 100644
--- a/kernel/kernel.cpp
+++ b/kernel/kernel.cpp
@@ -112,6 +112,7 @@ extern "C" void _start() {
 

     printf("hhdm offset: %lx\n", _hhdm_offset);

     pmm_init(memmap_request.response);

+    draw_pixel(100, 100, 0x0000ff);

 

     uint64_t tester = page_alloc();

     printf("tester: %lx\n", tester);

diff --git a/kernel/mm/pmm.cpp b/kernel/mm/pmm.cpp
index 685f038..d25e673 100644
--- a/kernel/mm/pmm.cpp
+++ b/kernel/mm/pmm.cpp
@@ -2,8 +2,13 @@
 #include <kernel.h>
 #include <stdio.h>
 
+#define PAGE_SIZE 0x1000ul
+// makes sure double frees aren't happening (probably)
+#define PMM_MAGIC_NUM 0xE1321ul
+
 struct freelist {
     freelist* next = nullptr;
+    uint64_t magic_num;
 };
 
 freelist* head = nullptr;
@@ -15,8 +20,9 @@ void pmm_init(limine_memmap_response* memmap) {
         if (memmap->entries[i]->type == LIMINE_MEMMAP_USABLE) {
             printf("%d\n", i);
             // iterates through all addresses
-            for (uint64_t addr = memmap->entries[i]->base; addr < (memmap->entries[i]->length + memmap->entries[i]->base); addr += 0x1000ul) {
+            for (uint64_t addr = memmap->entries[i]->base; addr < (memmap->entries[i]->length + memmap->entries[i]->base); addr += PAGE_SIZE) {
                 freelist* temp = (freelist*)(addr + _hhdm_offset);
+                temp->magic_num = PMM_MAGIC_NUM;
                 if (head) {
                     temp->next = head;
                     head = temp;
@@ -33,12 +39,20 @@ void pmm_init(limine_memmap_response* memmap) {
 
 uint64_t page_alloc() {
     freelist* alloced = head;
+    alloced->magic_num = 0;
     head = head->next;
     return (uint64_t)alloced;
 }
 
 void page_free(uint64_t page) {
     freelist* freed = (freelist*)page;
+
+    // double free check
+    if (freed->magic_num == PMM_MAGIC_NUM) {
+        return;
+    }
+
     freed->next = head;
+    freed->magic_num = PMM_MAGIC_NUM;
     head = freed;
 }
\ No newline at end of file