1 files changed, 14 insertions, 6 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 8469005..c9f0da9 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -67,12 +67,12 @@ struct task_struct *create_proc(void *bin, size_t len) {
   int c;
   size_t totpages, npages, ntables;
   void *p, *page, *tab, *map;
-  void *pdir, *stackt, *stackp;
+  void *pdir, *stackt, *stackp, *kstackp;
   struct task_struct *task = NULL;
 
   npages = pages(len);
   ntables = tables(pages(len));
-  totpages = npages + ntables + 3;
+  totpages = npages + ntables + 4;
 
   /* find an unused task structure */
   for(i = 0; i < NRTASKS; i++) {
@@ -102,8 +102,9 @@ struct task_struct *create_proc(void *bin, size_t len) {
    * will hold the binary image, the following
    * pages are allocated:
    *  - page directory (1 page)
-   *  - page tables
+   *  - page tables (1 per every 1024 pages)
    *  - stack page (1 page)
+   *  - kernel stack page (1 page)
    *  - stack table (1 page)
    */
   p = alloc_physical_pages(totpages);
@@ -113,6 +114,7 @@ struct task_struct *create_proc(void *bin, size_t len) {
   getpage(pdir, p);
   getpage(stackt, p);
   getpage(stackp, p);
+  getpage(kstackp, p);
 
   /* populate the page directory */
   c = npages;
@@ -141,7 +143,13 @@ struct task_struct *create_proc(void *bin, size_t len) {
   /* populate the stack table */
   map = map_page(stackt);
   empty_table(map);
-  ((uint32_t*) map)[PGENT - 1] = (uint32_t) stackp | 0x007;
+  ((uint32_t*) map)[PGENT - 3] = (uint32_t) stackp | 0x007;
+  /*
+   * NOTE: we leave a single 4KB gap between the kernel
+   * and user's stacks so we can detect overflows of the
+   * kernel's stack.
+   */
+  ((uint32_t*) map)[PGENT - 1] = (uint32_t) kstackp | 0x003;
 
   /* add the stack page table to the directory */
   map = map_page(pdir);
@@ -169,8 +177,8 @@ struct task_struct *create_proc(void *bin, size_t len) {
   task->state.gs = 0x23;
   task->state.ss = 0x23;
   task->state.eip = (uint32_t) USRSTART;
-  task->state.esp = 0xFFFFFFFF;
-  task->state.esp0 = 0x80000;
+  task->state.esp = 0xFFFFDFFF;
+  task->state.esp0 = 0xFFFFFFFF;
   task->state.ss0 = 0x10;
   __asm__ (
       "pushf\n" \