From f181215341f9c19d7e43e9f4a69a6b30ebf77482 Mon Sep 17 00:00:00 2001
From: belliash <belliash@codingworkshop.eu.org>
Date: Sat, 4 Feb 2023 00:17:07 +0100
Subject: [PATCH] Initialize segment registers

---
 xtoskrnl/ar/amd64/procsup.c  | 35 +++++++++++++++++++++++++++++++----
 xtoskrnl/includes/arpfuncs.h |  4 ++++
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/xtoskrnl/ar/amd64/procsup.c b/xtoskrnl/ar/amd64/procsup.c
index b64ab7b..37faa35 100644
--- a/xtoskrnl/ar/amd64/procsup.c
+++ b/xtoskrnl/ar/amd64/procsup.c
@@ -53,13 +53,16 @@ ArInitializeProcessor(VOID)
     ArLoadInterruptDescriptorTable(&IdtDescriptor.Limit);
     ArLoadTaskRegister((UINT)KGDT_SYS_TSS);
 
-    /* Set GS base */
-    ArWriteModelSpecificRegister(X86_MSR_GSBASE, (ULONGLONG)ProcessorBlock);
-    ArWriteModelSpecificRegister(X86_MSR_KERNEL_GSBASE, (ULONGLONG)ProcessorBlock);
-
     /* Enter passive IRQ level */
     ProcessorBlock->Irql = PASSIVE_LEVEL;
     ArWriteControlRegister(8, PASSIVE_LEVEL);
+
+    /* Initialize segment registers */
+    ArpInitializeSegments();
+
+    /* Set GS base */
+    ArWriteModelSpecificRegister(X86_MSR_GSBASE, (ULONGLONG)ProcessorBlock);
+    ArWriteModelSpecificRegister(X86_MSR_KERNEL_GSBASE, (ULONGLONG)ProcessorBlock);
 }
 
 /**
@@ -192,6 +195,30 @@ ArpInitializeProcessorBlock(OUT PKPROCESSOR_BLOCK ProcessorBlock,
     ProcessorBlock->Prcb.MxCsr = INITIAL_MXCSR;
 }
 
+/**
+ * Initializes segment registers.
+ *
+ * @return This routine does not return any value.
+ *
+ * @since XT 1.0
+ */
+XTAPI
+VOID
+ArpInitializeSegments(VOID)
+{
+    asm volatile("mov %0, %%ax\n"
+                 "mov %%ax, %%fs\n"
+                 "mov %1, %%ax\n"
+                 "mov %%ax, %%ds\n"
+                 "mov %%ax, %%es\n"
+                 "mov %%ax, %%gs\n"
+                 "swapgs\n"
+                 "mov %%ax, %%gs\n"
+                 :
+                 : "i" (KGDT_R3_CMTEB | RPL_MASK),
+                   "i" (KGDT_R3_DATA | RPL_MASK));
+}
+
 /**
  * Initializes the kernel's Task State Segment (TSS).
  *
diff --git a/xtoskrnl/includes/arpfuncs.h b/xtoskrnl/includes/arpfuncs.h
index d9c2e6b..c7f1677 100644
--- a/xtoskrnl/includes/arpfuncs.h
+++ b/xtoskrnl/includes/arpfuncs.h
@@ -116,6 +116,10 @@ ArpInitializeProcessorBlock(OUT PKPROCESSOR_BLOCK ProcessorBlock,
                             IN PKTSS Tss,
                             IN PVOID DpcStack);
 
+XTAPI
+VOID
+ArpInitializeSegments(VOID);
+
 XTAPI
 VOID
 ArpInitializeTss(IN PKPROCESSOR_BLOCK ProcessorBlock);