From 57482136ae25c624a2d9c19e12e6558027155f8f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Lov=C3=A9n?= <thomasloven@gmail.com>
Date: Sun, 24 Dec 2017 01:59:35 +0100
Subject: [PATCH] VMM - get_page fails if PTE not present

---
 src/kernel/memory/vmm.c  | 20 +++++++++++++++-----
 src/kernel/memory/vmm.tt | 35 ++++++++++++++++++++++++++---------
 2 files changed, 41 insertions(+), 14 deletions(-)

diff --git a/src/kernel/memory/vmm.c b/src/kernel/memory/vmm.c
index 775771e..5282bf7 100644
--- a/src/kernel/memory/vmm.c
+++ b/src/kernel/memory/vmm.c
@@ -6,7 +6,16 @@
 union PTE {
   uint64_t value;
   struct {
-    uintptr_t flags:12;
+    uintptr_t present:1;
+    uintptr_t write:1;
+    uintptr_t user:1;
+    uintptr_t write_through:1;
+    uintptr_t nocache:1;
+    uintptr_t accessed:1;
+    uintptr_t dirty:1;
+    uintptr_t huge:1;
+    uintptr_t global:1;
+    uintptr_t flags:3;
   };
 };
 
@@ -19,11 +28,12 @@ union PTE {
 uintptr_t vmm_get_page(void *P4, uintptr_t addr)
 {
   if(P4
-      && P4e(P4, addr).value
-      && P3e(P4, addr).value
-      && P2e(P4, addr).value
+      && P4e(P4, addr).present
+      && P3e(P4, addr).present
+      && P2e(P4, addr).present
+      && P1e(P4, addr).present
     )
     return MASK_FLAGS(P1e(P4, addr).value);
   else
-    return 0;
+    return -1;
 }
diff --git a/src/kernel/memory/vmm.tt b/src/kernel/memory/vmm.tt
index 07ae68e..ef52590 100644
--- a/src/kernel/memory/vmm.tt
+++ b/src/kernel/memory/vmm.tt
@@ -22,9 +22,12 @@ AFTER()
 TEST(get_page_returns_correct_address)
 {
   p4[0] = (uintptr_t)p3;
+  p4[0] |= PAGE_PRESENT;
   p3[0] = (uintptr_t)p2;
+  p3[0] |= PAGE_PRESENT;
   p2[0] = (uintptr_t)p1;
-  p1[0] = 0x1234567890ABC000;
+  p2[0] |= PAGE_PRESENT;
+  p1[0] = 0x1234567890ABC000 | PAGE_PRESENT;
 
   uintptr_t ret = vmm_get_page(p4, 0);
 
@@ -33,12 +36,12 @@ TEST(get_page_returns_correct_address)
 TEST(get_page_ignores_flags)
 {
   p4[0] = (uintptr_t)p3;
-  p4[0] |= 0x123;
+  p4[0] |= PAGE_PRESENT;
   p3[0] = (uintptr_t)p2;
-  p3[0] |= 0x456;
+  p3[0] |= PAGE_PRESENT;
   p2[0] = (uintptr_t)p1;
-  p2[0] |= 0x789;
-  p1[0] = 0x1234567890ABCDEF;
+  p2[0] |= PAGE_PRESENT;
+  p1[0] = 0x1234567890ABC000 | PAGE_PRESENT;
 
   uintptr_t ret = vmm_get_page(p4, 0);
 
@@ -47,14 +50,28 @@ TEST(get_page_ignores_flags)
 TEST(get_page_works_for_different_address)
 {
   p4[1] = (uintptr_t)p3;
-  p4[1] |= 0x123;
+  p4[1] |= PAGE_PRESENT;
   p3[2] = (uintptr_t)p2;
-  p3[2] |= 0x456;
+  p3[2] |= PAGE_PRESENT;
   p2[3] = (uintptr_t)p1;
-  p2[3] |= 0x789;
-  p1[4] = 0x34567890ABCDEF12;
+  p2[3] |= PAGE_PRESENT;
+  p1[4] = 0x34567890ABCDE000 | PAGE_PRESENT;
 
   uintptr_t ret = vmm_get_page(p4, (1UL<<39)+(2UL<<30)+(3UL<<21)+(4UL<<12));
 
   ASSERT_EQ_PTR(ret, 0x34567890ABCDE000);
 }
+TEST(get_page_fails_if_PTE_not_present)
+{
+  p4[0] = (uintptr_t)p3;
+  p4[0] |= PAGE_PRESENT;
+  p3[0] = (uintptr_t)p2;
+  p3[0] |= PAGE_PRESENT;
+  p2[0] = (uintptr_t)p1;
+  p2[0] |= 0;
+  p1[0] = 0x1234567890ABC000 | PAGE_PRESENT;
+
+  uintptr_t ret = vmm_get_page(p4, 0);
+
+  ASSERT_EQ_PTR(ret, -1);
+}