Attempt to make COM anti-malware work, find out that Mono is utterly broken

IPA.Loader/AntiMalware/AmsiConstants.cs

@@ -6,6 +6,9 @@ namespace IPA.AntiMalware
     internal static class AmsiConstants
     {
         public const string AppName = "BSIPA/" + Config.SelfConfig.IPAVersion;
+        public const string IAntimalwareGuidStr = "82d29c2e-f062-44e6-b5c9-3d9a2f24a2df";
+        public static readonly Guid IAntimalwareGuid = new(IAntimalwareGuidStr);
         public static readonly Guid CAntimalwareGuid = new("fdb00e52-a214-4aa1-8fba-4357bb0072ec");
+        public static readonly Guid IUnknownGuid = new("00000000-0000-0000-C000-000000000046");
     }
 }

IPA.Loader/AntiMalware/_HideInNet3/ComAPI/IAntimalware.cs

@@ -8,24 +8,27 @@ using System.Threading.Tasks;
 
 namespace IPA.AntiMalware.ComAPI
 {
-    [Guid("82d29c2e-f062-44e6-b5c9-3d9a2f24a2df")]
-    [ComVisible(true)]
+    [ComImport]
+    [Guid(AmsiConstants.IAntimalwareGuidStr)]
+    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
     internal interface IAntimalware
     {
         void Scan([In] IAmsiStream stream, [Out] out AmsiResult result, [Out] out IAntimalwareProvider provider);
         void CloseSession([In] ulong session);
     }
 
+    [ComImport]
     [Guid("3e47f2e5-81d4-4d3b-897f-545096770373")]
-    [ComVisible(true)]
+    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
     internal interface IAmsiStream
     {
-        unsafe void GetAttribute([In] AmsiAttribute attribute, [In] uint dataSize, [Out] byte* buffer, out uint writtenData);
-        unsafe void Read([In] ulong position, [In] uint dataSize, [Out] byte* buffer, out uint readSize);
+        unsafe void GetAttribute([In] AmsiAttribute attribute, [In] uint dataSize, [Out] byte* buffer, [Out] out uint writtenData);
+        unsafe void Read([In] ulong position, [In] uint dataSize, [Out] byte* buffer, [Out] out uint readSize);
     }
 
+    [ComImport]
     [Guid("b2cabfe3-fe04-42b1-a5df-08d483d4d125")]
-    [ComVisible(true)]
+    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
     internal interface IAntimalwareProvider
     {
         [return: MarshalAs(UnmanagedType.LPWStr)] string DisplayName();

IPA.Loader/AntiMalware/_HideInNet3/WindowsCOMAntiMalware.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading.Tasks;
 
@@ -14,6 +15,9 @@ namespace IPA.AntiMalware
     {
         internal static WindowsCOMAntiMalware? TryInitialize()
         {
+            // Mono's COM interop *fundamentally doesn't work.*
+            // End of story.
+#if false
             try
             {
                 return new();
@@ -22,18 +26,39 @@ namespace IPA.AntiMalware
             {
                 Logger.AntiMalware.Warn("Could not initialize COM-based antimalware engine:");
                 Logger.AntiMalware.Warn(e);
-                return null;
             }
+#endif
+            return null;
         }
 
         private readonly IAntimalware amInterface;
 
         private WindowsCOMAntiMalware()
         {
-            var amType = Type.GetTypeFromCLSID(AmsiConstants.CAntimalwareGuid, true);
-            amInterface = (IAntimalware)Activator.CreateInstance(amType);
+            var hr = CoCreateInstanceAM(AmsiConstants.CAntimalwareGuid,
+                null,
+                0x1 | 0x4 /* inproc server, local server */,
+                AmsiConstants.IAntimalwareGuid,
+                out var antimalware);
+            Marshal.ThrowExceptionForHR(hr);
+
+            amInterface = antimalware;
         }
 
+        [DllImport("ole32",
+            CallingConvention = CallingConvention.Winapi,
+            ExactSpelling = true,
+            PreserveSig = false,
+            EntryPoint = "CoCreateInstance")]
+        [DefaultDllImportSearchPaths(DllImportSearchPath.System32)]
+        private static extern int CoCreateInstanceAM(
+            [In] in Guid clsid,
+            [In, MarshalAs(UnmanagedType.Interface)] object? unkOuter,
+            [In] int dwClsContext,
+            [In] in Guid iid,
+            [Out, MarshalAs(UnmanagedType.Interface)] out IAntimalware @interface);
+
+
         private static ScanResult ScanResultFromAmsiResult(AmsiResult result)
             => result switch
             {