From e68698ff808d89ffa621bcf07ae706a9d2083ac3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Lov=C3=A9n?= <thomasloven@gmail.com>
Date: Tue, 2 Jan 2018 12:24:02 +0100
Subject: [PATCH] VMM - set_page does not overwrite 4kb pages with 2mb

---
 src/kernel/memory/vmm.c  | 2 ++
 src/kernel/memory/vmm.tt | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/src/kernel/memory/vmm.c b/src/kernel/memory/vmm.c
index 1085705..595e443 100644
--- a/src/kernel/memory/vmm.c
+++ b/src/kernel/memory/vmm.c
@@ -56,6 +56,8 @@ int vmm_set_page(void *P4, uintptr_t addr, uintptr_t page, uint16_t flags)
           && P3e(P4, addr).present
         ))
       return -1;
+    if(P2e(P4, addr).present && !P2e(P4,addr).huge)
+      return -1;
     P2e(P4, addr).value = page | flags;
     return 0;
   }
diff --git a/src/kernel/memory/vmm.tt b/src/kernel/memory/vmm.tt
index 9ab0b0f..161b0a6 100644
--- a/src/kernel/memory/vmm.tt
+++ b/src/kernel/memory/vmm.tt
@@ -106,6 +106,14 @@ TEST(set_page_sets_2mb_pages)
 
   ASSERT_EQ_PTR(p2[3], 0x1234567890A00000 | PAGE_HUGE | PAGE_PRESENT);
 }
+TEST(set_page_does_not_overwrite_4kb_pages_with_2mb)
+{
+  BUILD_PT(0,0,0);
+
+  int retval = vmm_set_page(p4, 0, 0, PAGE_HUGE | PAGE_PRESENT);
+
+  ASSERT_NEQ_INT(retval, 0);
+}
 
 uintptr_t pmm_alloc()
 {