From 4c4e7136cce90f264176a77bc6eb7127c6315dfd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Lov=C3=A9n?= <thomasloven@gmail.com>
Date: Wed, 7 Mar 2018 21:17:06 +0100
Subject: [PATCH] Handle pagefaults caused by running of the stack

---
 src/kernel/proc/procmm.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/src/kernel/proc/procmm.c b/src/kernel/proc/procmm.c
index c30ebdc..c9edee0 100644
--- a/src/kernel/proc/procmm.c
+++ b/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;
 }