Fix 32-bit thread context API selection in DllInjector

Because DllInjector enforces matching host/target bitness, a 32-bit caller
always handles a 32-bit target. The correct API is native
GetThreadContext/SetThreadContext with Context32; the Wow64 APIs are only for
64-bit processes inspecting WOW64 targets, which never happens here.

- Collapse the 32-bit path to always use GetThreadContext/SetThreadContext.
- Remove the now-unused Wow64GetThreadContext/Wow64SetThreadContext
  declarations.
- Update Context32 doc comment to describe the x86 usage.
- ExternalReader access guard now also accepts QueryLimitedInformation.

Tests: 207 passing, 4 skipped.

WhiteMagic/ExternalReader.cs

@@ -37,10 +37,11 @@ public sealed class ExternalReader : MemoryBase
     public ExternalReader(System.Diagnostics.Process process, ProcessAccess desiredAccess = DefaultAccess)
     {
         _processId = process.Id;
-        if ((desiredAccess & ProcessAccess.QueryInformation) == 0)
+        const ProcessAccess queryAccess = ProcessAccess.QueryInformation | ProcessAccess.QueryLimitedInformation;
+        if ((desiredAccess & queryAccess) == 0)
         {
             throw new ArgumentException(
-                "ExternalReader requires ProcessAccess.QueryInformation to determine target bitness.",
+                "ExternalReader requires ProcessAccess.QueryInformation or ProcessAccess.QueryLimitedInformation to determine target bitness.",
                 nameof(desiredAccess));
         }
 

WhiteMagic/Injection/DllInjector.cs

@@ -215,7 +215,7 @@ public sealed class DllInjector
             {
                 IntPtr result;
 
-                if (Environment.Is64BitProcess)
+                if (_currentIs64Bit)
                 {
                     var originalContext = new Context64 { ContextFlags = ContextFlags.Amd64Full };
                     if (!NativeMethods.GetThreadContext(thread, ref originalContext))
@@ -264,32 +264,23 @@ public sealed class DllInjector
                 }
                 else
                 {
-                    // 32-bit process on either a 32-bit or 64-bit (WOW64) host.
+                    // 32-bit process targeting a 32-bit process. The target context is
-                    bool useWow64 = Environment.Is64BitOperatingSystem;
+                    // a native x86 CONTEXT; the WOW64 APIs are for 64-bit callers only.
-
                     var originalContext = new Context32 { ContextFlags = ContextFlags.X86Full };
-                    bool gotContext = useWow64
+                    if (!NativeMethods.GetThreadContext(thread, ref originalContext))
-                        ? NativeMethods.Wow64GetThreadContext(thread, ref originalContext)
-                        : NativeMethods.GetThreadContext(thread, ref originalContext);
-                    if (!gotContext)
                     {
                         int error = Marshal.GetLastPInvokeError();
-                        string api = useWow64 ? "Wow64GetThreadContext" : "GetThreadContext";
+                        throw new InvalidOperationException($"GetThreadContext failed (error {error}).");
-                        throw new InvalidOperationException($"{api} failed (error {error}).");
                     }
 
                     var redirectContext = originalContext;
                     redirectContext.Eip = (uint)(nint)remoteBase;
                     redirectContext.Esp = (uint)(nint)stackTop;
 
-                    bool setContext = useWow64
+                    if (!NativeMethods.SetThreadContext(thread, ref redirectContext))
-                        ? NativeMethods.Wow64SetThreadContext(thread, ref redirectContext)
-                        : NativeMethods.SetThreadContext(thread, ref redirectContext);
-                    if (!setContext)
                     {
                         int error = Marshal.GetLastPInvokeError();
-                        string api = useWow64 ? "Wow64SetThreadContext" : "SetThreadContext";
+                        throw new InvalidOperationException($"SetThreadContext failed (error {error}).");
-                        throw new InvalidOperationException($"{api} failed (error {error}).");
                     }
 
                     if (NativeMethods.ResumeThread(thread) == 0xFFFFFFFF)
@@ -306,14 +297,10 @@ public sealed class DllInjector
                         throw new InvalidOperationException($"SuspendThread failed while capturing result (error {error}).");
                     }
 
-                    bool restoredContext = useWow64
+                    if (!NativeMethods.SetThreadContext(thread, ref originalContext))
-                        ? NativeMethods.Wow64SetThreadContext(thread, ref originalContext)
-                        : NativeMethods.SetThreadContext(thread, ref originalContext);
-                    if (!restoredContext)
                     {
                         int error = Marshal.GetLastPInvokeError();
-                        string api = useWow64 ? "Wow64SetThreadContext" : "SetThreadContext";
+                        throw new InvalidOperationException($"SetThreadContext restore failed (error {error}).");
-                        throw new InvalidOperationException($"{api} restore failed (error {error}).");
                     }
 
                     if (NativeMethods.ResumeThread(thread) == 0xFFFFFFFF)

WhiteMagic/Native/NativeMethods.cs

@@ -152,19 +152,6 @@ internal static partial class NativeMethods
         SafeMemoryHandle thread,
         ref Context32 context);
 
-    /// <summary>Sets a 32-bit (WOW64) thread context.</summary>
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    [return: MarshalAs(UnmanagedType.Bool)]
-    internal static partial bool Wow64SetThreadContext(
-        SafeMemoryHandle thread,
-        ref Context32 context);
-
-    /// <summary>Gets a 32-bit (WOW64) thread context.</summary>
-    [LibraryImport("kernel32.dll", SetLastError = true)]
-    [return: MarshalAs(UnmanagedType.Bool)]
-    internal static partial bool Wow64GetThreadContext(
-        SafeMemoryHandle thread,
-        ref Context32 context);
 
     // ── Modules ──────────────────────────────────────────────────────────────
 

WhiteMagic/Native/NativeStructures.cs

@@ -29,8 +29,8 @@ public unsafe struct FloatingSaveArea32
 }
 
 /// <summary>
-/// A 32-bit (x86/WOW64) thread context. Use it with
+/// A 32-bit x86 thread context. Use it with <c>GetThreadContext</c> and
-/// <c>Wow64GetThreadContext</c> and <c>Wow64SetThreadContext</c> to inspect a 32-bit thread.
+/// <c>SetThreadContext</c> from a 32-bit process targeting a 32-bit thread.
 /// The total size is 716 bytes.
 /// </summary>
 [StructLayout(LayoutKind.Sequential)]