From 362eefc2b3e3f704535932152200f3542c8f9660 Mon Sep 17 00:00:00 2001
From: belliash <belliash@codingworkshop.eu.org>
Date: Tue, 7 Nov 2023 15:34:49 +0100
Subject: [PATCH] Fixes in AMD64 version of KepInitializeThreadContext() to get
 rid of PageFault exception

---
 sdk/xtdk/amd64/ketypes.h    |  8 +++++++-
 xtoskrnl/ke/amd64/kthread.c | 12 ++++++------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/sdk/xtdk/amd64/ketypes.h b/sdk/xtdk/amd64/ketypes.h
index f322c41..d5b8ab0 100644
--- a/sdk/xtdk/amd64/ketypes.h
+++ b/sdk/xtdk/amd64/ketypes.h
@@ -139,6 +139,11 @@
 /* Size of legacy 387 registers */
 #define SIZE_OF_80387_REGISTERS           80
 
+/* NPX state definitions */
+#define NPX_STATE_UNUSED                  0x0
+#define NPX_STATE_SCRUB                   0x1
+#define NPX_STATE_SWITCH                  0x2
+
 /* Floating point state storing structure */
 typedef struct _FLOATING_SAVE_AREA
 {
@@ -352,7 +357,8 @@ typedef struct _KSWITCH_FRAME
     ULONG64 P4Home;
     ULONG64 P5Home;
     ULONG MxCsr;
-    UCHAR Reserved[4];
+    KIRQL ApcBypass;
+    UCHAR Reserved[3];
     ULONG64 Rbp;
     ULONG64 Return;
 } KSWITCH_FRAME, *PKSWITCH_FRAME;
diff --git a/xtoskrnl/ke/amd64/kthread.c b/xtoskrnl/ke/amd64/kthread.c
index d015456..7104b57 100644
--- a/xtoskrnl/ke/amd64/kthread.c
+++ b/xtoskrnl/ke/amd64/kthread.c
@@ -42,7 +42,7 @@ KepInitializeThreadContext(IN PKTHREAD Thread,
     PKTHREAD_INIT_FRAME ThreadFrame;
 
     /* Set initial thread frame */
-    ThreadFrame = (PKTHREAD_INIT_FRAME)Thread->InitialStack - sizeof(KTHREAD_INIT_FRAME);
+    ThreadFrame = ((PKTHREAD_INIT_FRAME)Thread->InitialStack) - 1;
 
     /* Fill floating point save area with zeroes */
     RtlZeroMemory(&ThreadFrame->NpxFrame, sizeof(FLOATING_SAVE_AREA));
@@ -68,7 +68,7 @@ KepInitializeThreadContext(IN PKTHREAD Thread,
         Thread->PreviousMode = UserMode;
 
         /* Enable floating point state */
-        Thread->NpxState = 1;
+        Thread->NpxState = NPX_STATE_SCRUB;
 
         /* Set initial floating point state */
         ThreadFrame->NpxFrame.ControlWord = 0x27F;
@@ -93,9 +93,9 @@ KepInitializeThreadContext(IN PKTHREAD Thread,
         Thread->PreviousMode = KernelMode;
 
         /* Disable floating point state */
-        Thread->NpxState = 0;
+        Thread->NpxState = NPX_STATE_UNUSED;
 
-        /* Set thread startup frame return information */
+        /* Set thread start address */
         ThreadFrame->StartFrame.Return = (ULONG64)NULL;
     }
 
@@ -106,10 +106,10 @@ KepInitializeThreadContext(IN PKTHREAD Thread,
     ThreadFrame->StartFrame.P4Home = (ULONG64)SystemRoutine;
 
     /* Initialize switch frame */
-    ThreadFrame->SwitchFrame.Rbp = (ULONG64)&ThreadFrame->TrapFrame + 128;
+    ThreadFrame->SwitchFrame.ApcBypass = APC_LEVEL;
     ThreadFrame->SwitchFrame.MxCsr = INITIAL_MXCSR;
+    ThreadFrame->SwitchFrame.Rbp = (ULONG64)&ThreadFrame->TrapFrame;
 
     /* Set thread stack */
-    Thread->InitialStack = &ThreadFrame->NpxFrame;
     Thread->KernelStack = &ThreadFrame->SwitchFrame;
 }