From 64df03c2303bfe47a259e397aad54ee301c390d5 Mon Sep 17 00:00:00 2001
From: Thomas Oltmann <thomas.oltmann.hhg@gmail.com>
Date: Mon, 10 Mar 2025 20:24:32 +0100
Subject: [PATCH] Calling VMXON

---
 include/x86/cr.h  |  8 ++++++++
 include/x86/msr.h |  2 +-
 include/x86/vmx.h | 19 ++++++++++++++----
 src/efi.c         |  6 ++++++
 src/vintel.c      | 50 +++++++++++++++++++++++++++++++++++------------
 src/virt.h        |  1 +
 6 files changed, 69 insertions(+), 17 deletions(-)

diff --git a/include/x86/cr.h b/include/x86/cr.h
index e14a77e..83b3bf2 100644
--- a/include/x86/cr.h
+++ b/include/x86/cr.h
@@ -3,6 +3,8 @@
 
 #include <stdint.h>
 
+#define CR4_VMXE (1 << 13)
+
 static inline uint64_t
 readcr0(void)
 {
@@ -27,4 +29,10 @@ readcr4(void)
 	return v;
 }
 
+static inline void
+writecr4(uint64_t v)
+{
+	__asm__ ("mov %0, %%cr4\n\t" :: "a"(v));
+}
+
 #endif
diff --git a/include/x86/msr.h b/include/x86/msr.h
index 21a6f69..a889613 100644
--- a/include/x86/msr.h
+++ b/include/x86/msr.h
@@ -21,7 +21,7 @@ static inline uint32_t
 rdmsr32(uint32_t msr)
 {
 	uint32_t value;
-	__asm__ ("rdmsr\n\t" : "=a"(value) : "c"(msr) : "d");
+	__asm__ ("rdmsr\n\t" : "=a"(value) : "c"(msr) : "edx");
 	return value;
 }
 
diff --git a/include/x86/vmx.h b/include/x86/vmx.h
index 83a909b..1d358c0 100644
--- a/include/x86/vmx.h
+++ b/include/x86/vmx.h
@@ -3,10 +3,14 @@
 
 #include <stdint.h>
 
-struct VMCS {
-	/* VMCS Header */
+struct VMXON {
 	uint32_t revisionID;
 	uint32_t abortIndicator;
+	char     vmcsData[];
+};
+
+struct VMCS {
+	int _placeholder;
 	/* Guest-state area */
 	/* Host-state area */
 	/* VM-execution control fields */
@@ -15,10 +19,17 @@ struct VMCS {
 	/* VM-exit information fields */
 };
 
-static inline void
+static inline uint64_t
 vmxon(void *region)
 {
-	__asm__ volatile ("vmxon %0\n\t" :: "r"(region));
+	uint64_t regionpa = (uint64_t)region;
+	uint64_t flags;
+	__asm__ volatile (
+		"vmxon %1\n\t"
+		"pushf   \n\t"
+		"pop   %0\n\t"
+		: "=r"(flags) : "m"(regionpa));
+	return flags;
 }
 
 static inline void
diff --git a/src/efi.c b/src/efi.c
index f79b36d..8d93257 100644
--- a/src/efi.c
+++ b/src/efi.c
@@ -14,10 +14,16 @@ EFI_STATUS
 efi_main(EFI_HANDLE imageHandle, EFI_SYSTEM_TABLE *systemTable)
 {
 	InitializeLib(imageHandle, systemTable);
+
 	Print(L"Hello, World!\n");
 
+	AsciiPrint("* Checking for VT-x Support\n");
 	if (!virt->has_support(virt_err, sizeof virt_err)) {
 		AsciiPrint(virt_err);
+	} else {
+		AsciiPrint("* Enabling VT-x\n");
+		virt->enable();
+		AsciiPrint("* VT-x enabled!\n");
 	}
 
 	for (;;) {}
diff --git a/src/vintel.c b/src/vintel.c
index 91772f8..f556a55 100644
--- a/src/vintel.c
+++ b/src/vintel.c
@@ -1,10 +1,17 @@
+#include <efi.h>
+#include <efilib.h>
+#include <efiapi.h>
+
 #include <cpuid.h>
 #include <x86/msr.h>
 #include <x86/cr.h>
+#include <x86/vmx.h>
 
 #include "virt.h"
 #include "std.h"
 
+static struct VMXON *vmxon_region;
+
 static bool
 vintel_has_bios_support(void)
 {
@@ -20,13 +27,6 @@ vintel_has_cpu_support(void)
 	return (info[2] & (1 << 5)) != 0;
 }
 
-static bool
-vintel_has_cr4_support(void)
-{
-	uint64_t value = readcr4();
-	return (value & (1 << 13)) != 0;
-}
-
 bool
 vintel_has_support(char *err, size_t errmax)
 {
@@ -40,14 +40,40 @@ vintel_has_support(char *err, size_t errmax)
 		return false;
 	}
 
-	if (!vintel_has_cr4_support()) {
-		strlcpy(err, "VT-x enable bit is not set in CR4.", errmax);
-		return false;
-	}
-
 	return true;
 }
 
+void
+vintel_enable(void)
+{
+	Print(L"Set CR4 Bit\n");
+	writecr4(readcr4() | CR4_VMXE);
+
+#if 0
+	Print(L"Enable in Feature Control\n");
+	uint64_t fctl = rdmsr64(IA32_FEATURE_CONTROL);
+	fctl |= (1 << 0);
+	wrmsr64(IA32_FEATURE_CONTROL, fctl);
+#endif
+
+	Print(L"Allocating VMXON Page\n");
+	uefi_call_wrapper(BS->AllocatePages, 4, AllocateAnyPages, EfiRuntimeServicesData, 1, &vmxon_region);
+
+	Print(L"VMCS: %p\n", vmxon_region);
+	vmxon_region->revisionID = rdmsr32(IA32_VMX_BASIC);
+	Print(L"Set Revision ID.\n");
+
+	uint64_t status = vmxon(vmxon_region);
+	Print(L"VMXON Status: %p\n", (void *)status);
+	if (status & (1 << 0)) {
+		Print(L"Invalid VMCS Pointer\n");
+	}
+	if (status & (1 << 6)) {
+		Print(L"Extended VMX Error\n");
+	}
+}
+
 struct virt_vtable virt_vtable_intel = {
 	.has_support = vintel_has_support,
+	.enable      = vintel_enable,
 };
diff --git a/src/virt.h b/src/virt.h
index 542aec9..6d0ee7e 100644
--- a/src/virt.h
+++ b/src/virt.h
@@ -6,6 +6,7 @@
 
 struct virt_vtable {
 	bool (*has_support)(char *err, size_t errmax);
+	void (*enable)(void);
 };
 
 extern struct virt_vtable virt_vtable_intel;