NtAllocateVirtualMemory

[DllImport("ntdll.dll", ExactSpelling = true)]
[DefaultDllImportSearchPaths(DllImportSearchPath.System32)]
public static extern unsafe NTSTATUS NtAllocateVirtualMemory(
    HANDLE ProcessHandle,
    void* BaseAddress,
    uint ZeroBits,
    uint* RegionSize,
    uint AllocationType,
    uint Protect);

VIRTUAL_ALLOCATION_TYPE

PAGE_PROTECTION_FLAGS