From b2e9c8eea5d4f4edb43ae7be9e15986dbfce5b95 Mon Sep 17 00:00:00 2001
From: Frans Kaashoek <kaashoek@mit.edu>
Date: Mon, 22 Jul 2019 15:38:08 -0400
Subject: Clear U bit for second stack page so that it functions as a guard
 page

---
 kernel/vm.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'kernel/vm.c')

diff --git a/kernel/vm.c b/kernel/vm.c
index 96f2ffa..cbea684 100644
--- a/kernel/vm.c
+++ b/kernel/vm.c
@@ -436,3 +436,13 @@ kernelpa(uint64 va) {
   pa = PTE2PA(*pte);
   return pa+off;
 }
+
+void
+clearpteu(pagetable_t pagetable, uint64 va) {
+  pte_t *pte;
+  
+  pte = walk(pagetable, va, 0);
+  if(pte == 0)
+    panic("clearpteu");
+  *pte &= ~PTE_U;
+}
-- 
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