Handle pagefaults caused by running of the stack

src/kernel/proc/procmm.c

@@ -34,7 +34,22 @@ registers *proc_pagefault(registers *r)
     PANIC("Page fault in kernel\n");
   }
 
-  PANIC("Page fault in process\n");
+  uint64_t fault_addr = read_cr2();
+  uint64_t stack = PROCESS()->stack;
+  if(fault_addr + PAGE_SIZE >= stack)
+  {
+    // Page fault happened just below stack. Add another page to it.
+    // Unless it's about to run into brk.
+    if(stack - PAGE_SIZE <= PROCESS()->brk)
+      PANIC("Stack overflow in process %d\n", PROCESS()->pid);
 
+    stack -= PAGE_SIZE;
+    vmm_set_page(PROCESS()->P4, stack, pmm_alloc(), PAGE_USER | PAGE_WRITE | PAGE_PRESENT);
+    PROCESS()->stack = stack;
+
+    return r;
+  }
+
+  PANIC("Page fault in process\n");
   return r;
 }