From e685b25e35c9d6dfbe2139ac71f7378b1f9e6d0f Mon Sep 17 00:00:00 2001
From: Timo Kreuzer <timo.kreuzer@reactos.org>
Date: Thu, 28 Sep 2023 20:29:43 +0300
Subject: [PATCH] [NTOS:MM/x64] Temporarily release AddressCreationLock in
 MmCreateVirtualMappingUnsafeEx

This is a hack, because the kernel mode path can incur a recursive page fault with the AddressCreationLock acquired, which would lead to a recursive acquisition, once we do proper locking in MmAccessFault.
To properly fix this the PDE must be made valid, similar to the user mode path, but that is not that simple...
---
 ntoskrnl/mm/i386/page.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/ntoskrnl/mm/i386/page.c b/ntoskrnl/mm/i386/page.c
index df13cb013e2..eeccef94346 100644
--- a/ntoskrnl/mm/i386/page.c
+++ b/ntoskrnl/mm/i386/page.c
@@ -637,6 +637,9 @@ MmCreateVirtualMappingUnsafeEx(
     PMMPTE PointerPte;
     MMPTE TempPte;
     ULONG_PTR Pte;
+#ifdef _M_AMD64
+    BOOLEAN LockReleased = FALSE;
+#endif
 
     DPRINT("MmCreateVirtualMappingUnsafe(%p, %p, %lu, %x)\n",
            Process, Address, flProtect, Page);
@@ -665,6 +668,15 @@ MmCreateVirtualMappingUnsafeEx(
         if (!MiSynchronizeSystemPde(MiAddressToPde(Address)))
             MiFillSystemPageDirectory(Address, PAGE_SIZE);
 #endif
+
+#ifdef _M_AMD64
+        /* This is a temporary hack, because we can incur a recursive page fault when accessing the PDE */
+        if (PsIdleProcess->AddressCreationLock.Owner == KeGetCurrentThread())
+        {
+            MmUnlockAddressSpace(MmGetKernelAddressSpace());
+            LockReleased = TRUE;
+        }
+#endif
     }
     else
     {
@@ -715,6 +727,15 @@ MmCreateVirtualMappingUnsafeEx(
         MiIncrementPageTableReferences(Address);
         MiUnlockProcessWorkingSetUnsafe(Process, PsGetCurrentThread());
     }
+#ifdef _M_AMD64
+    else
+    {
+        if (LockReleased)
+        {
+            MmLockAddressSpace(MmGetKernelAddressSpace());
+        }
+    }
+#endif
 
     return(STATUS_SUCCESS);
 }