Author: tkreuzer
Date: Wed Oct  8 00:31:35 2014
New Revision: 64591

URL: http://svn.reactos.org/svn/reactos?rev=64591&view=rev
Log:
[NTOSKRNL]
- Improve the random address base code in MiCreatePebOrTeb to actually make sense and not rely on retarded hacks implicitly hardcoding the PEB size in pages into the random value generation.

Modified:
    trunk/reactos/ntoskrnl/mm/ARM3/procsup.c

Modified: trunk/reactos/ntoskrnl/mm/ARM3/procsup.c
URL: http://svn.reactos.org/svn/reactos/trunk/reactos/ntoskrnl/mm/ARM3/procsup.c?rev=64591&r1=64590&r2=64591&view=diff
==============================================================================
--- trunk/reactos/ntoskrnl/mm/ARM3/procsup.c    [iso-8859-1] (original)
+++ trunk/reactos/ntoskrnl/mm/ARM3/procsup.c    [iso-8859-1] Wed Oct  8 00:31:35 2014
@@ -48,13 +48,13 @@
 NTAPI
 MiCreatePebOrTeb(IN PEPROCESS Process,
                  IN ULONG Size,
-                 OUT PULONG_PTR Base)
+                 OUT PULONG_PTR BaseAddress)
 {
     PETHREAD Thread = PsGetCurrentThread();
     PMMVAD_LONG Vad;
     NTSTATUS Status;
-    ULONG RandomCoeff;
-    ULONG_PTR StartAddress, EndAddress;
+    ULONG_PTR HighestAddress, RandomBase;
+    ULONG AlignedSize;
     LARGE_INTEGER CurrentTime;
     TABLE_SEARCH_RESULT Result = TableFoundNode;
     PMMADDRESS_NODE Parent;
@@ -83,25 +83,30 @@
     /* Check if this is a PEB creation */
     if (Size == sizeof(PEB))
     {
-        /* Start at the highest valid address */
-        StartAddress = (ULONG_PTR)MM_HIGHEST_VAD_ADDRESS + 1;
-
-        /* Select the random coefficient */
+        /* Create a random value to select one page in a 64k region */
         KeQueryTickCount(&CurrentTime);
-        CurrentTime.LowPart &= ((64 * _1KB) >> PAGE_SHIFT) - 1;
-        if (CurrentTime.LowPart <= 1) CurrentTime.LowPart = 2;
-        RandomCoeff = CurrentTime.LowPart << PAGE_SHIFT;
-
-        /* Select the highest valid address minus the random coefficient */
-        StartAddress -= RandomCoeff;
-        EndAddress = StartAddress + ROUND_TO_PAGES(Size) - 1;
+        CurrentTime.LowPart &= (_64K / PAGE_SIZE) - 1;
+
+        /* Calculate a random base address */
+        RandomBase = (ULONG_PTR)MM_HIGHEST_VAD_ADDRESS + 1;
+        RandomBase -= CurrentTime.LowPart << PAGE_SHIFT;
+
+        /* Make sure the base address is not too high */
+        AlignedSize = ROUND_TO_PAGES(Size);
+        if ((RandomBase + AlignedSize) > (ULONG_PTR)MM_HIGHEST_VAD_ADDRESS + 1)
+        {
+            RandomBase = (ULONG_PTR)MM_HIGHEST_VAD_ADDRESS + 1 - AlignedSize;
+        }
+
+        /* Calculate the highest allowed address */
+        HighestAddress = RandomBase + AlignedSize - 1;

         /* Try to find something below the random upper margin */
         Result = MiFindEmptyAddressRangeDownTree(ROUND_TO_PAGES(Size),
-                                                 EndAddress,
+                                                 HighestAddress,
                                                  PAGE_SIZE,
                                                  &Process->VadRoot,
-                                                 Base,
+                                                 BaseAddress,
                                                  &Parent);
     }

@@ -113,7 +118,7 @@
                                                  (ULONG_PTR)MM_HIGHEST_VAD_ADDRESS,
                                                  PAGE_SIZE,
                                                  &Process->VadRoot,
-                                                 Base,
+                                                 BaseAddress,
                                                  &Parent);
         /* Bail out, if still nothing free was found */
         if (Result == TableFoundNode)
@@ -125,12 +130,12 @@
     }

     /* Validate that it came from the VAD ranges */
-    ASSERT(*Base >= (ULONG_PTR)MI_LOWEST_VAD_ADDRESS);
+    ASSERT(*BaseAddress >= (ULONG_PTR)MI_LOWEST_VAD_ADDRESS);

     /* Build the rest of the VAD now */
-    Vad->StartingVpn = (*Base) >> PAGE_SHIFT;
-    Vad->EndingVpn = ((*Base) + Size - 1) >> PAGE_SHIFT;
-    Vad->u3.Secured.StartVpn = *Base;
+    Vad->StartingVpn = (*BaseAddress) >> PAGE_SHIFT;
+    Vad->EndingVpn = ((*BaseAddress) + Size - 1) >> PAGE_SHIFT;
+    Vad->u3.Secured.StartVpn = *BaseAddress;
     Vad->u3.Secured.EndVpn = (Vad->EndingVpn << PAGE_SHIFT) | (PAGE_SIZE - 1);
     Vad->u1.Parent = NULL;

@@ -146,7 +151,7 @@
     Vad->ControlArea = NULL; // For Memory-Area hack
     Vad->FirstPrototypePte = NULL;
     DPRINT("VAD: %p\n", Vad);
-    DPRINT("Allocated PEB/TEB at: 0x%p for %16s\n", *Base, Process->ImageFileName);
+    DPRINT("Allocated PEB/TEB at: 0x%p for %16s\n", *BaseAddress, Process->ImageFileName);
     MiInsertNode(&Process->VadRoot, (PVOID)Vad, Parent, Result);

     /* Release the working set */