From 8400e15b80c0e3d4b32acd32bd3c4be5c52c15c0 Mon Sep 17 00:00:00 2001
From: Brennan <brecon@microsoft.com>
Date: Mon, 19 May 2025 20:40:55 -0700
Subject: [PATCH] [IIS] Manually parse exe bitness (#61894)

---
 .../CommonLib/HostFxrResolver.cpp             | 72 +++++++++++++++----
 .../CommonLib/HostFxrResolver.h               |  2 +
 src/Servers/IIS/build/Build.Lib.Settings      |  2 +-
 3 files changed, 63 insertions(+), 13 deletions(-)

diff --git a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
index 9b12cd0132b4..8fb960261590 100644
--- a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
+++ b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
@@ -197,7 +197,7 @@ HostFxrResolver::TryGetHostFxrPath(
     size_t size = MAX_PATH * 2;
     hostfxrPath.resize(size);
 
-    get_hostfxr_parameters params;
+    get_hostfxr_parameters params{};
     params.size = sizeof(get_hostfxr_parameters);
     params.assembly_path = applicationPath.c_str();
     params.dotnet_root = dotnetRoot.c_str();
@@ -393,7 +393,7 @@ HostFxrResolver::GetAbsolutePathToDotnetFromHostfxr(const fs::path& hostfxrPath)
 // Tries to call where.exe to find the location of dotnet.exe.
 // Will check that the bitness of dotnet matches the current
 // worker process bitness.
-// Returns true if a valid dotnet was found, else false.R
+// Returns true if a valid dotnet was found, else false.
 //
 std::optional<fs::path>
 HostFxrResolver::InvokeWhereToFindDotnet()
@@ -415,8 +415,7 @@ HostFxrResolver::InvokeWhereToFindDotnet()
     DWORD               dwExitCode;
     STRU                struDotnetSubstring;
     STRU                struDotnetLocationsString;
-    DWORD               dwNumBytesRead;
-    DWORD               dwBinaryType;
+    DWORD               dwNumBytesRead = 0;
     INT                 index = 0;
     INT                 prevIndex = 0;
     std::optional<fs::path> result;
@@ -521,14 +520,7 @@ HostFxrResolver::InvokeWhereToFindDotnet()
 
         LOG_INFOF(L"Processing entry '%ls'", struDotnetSubstring.QueryStr());
 
-        if (LOG_LAST_ERROR_IF(!GetBinaryTypeW(struDotnetSubstring.QueryStr(), &dwBinaryType)))
-        {
-            continue;
-        }
-
-        LOG_INFOF(L"Binary type %d", dwBinaryType);
-
-        if (fIsCurrentProcess64Bit == (dwBinaryType == SCS_64BIT_BINARY))
+        if (fIsCurrentProcess64Bit == IsX64(struDotnetSubstring.QueryStr()))
         {
             // The bitness of dotnet matched with the current worker process bitness.
             return std::make_optional(struDotnetSubstring.QueryStr());
@@ -539,6 +531,62 @@ HostFxrResolver::InvokeWhereToFindDotnet()
     return result;
 }
 
+BOOL HostFxrResolver::IsX64(const WCHAR* dotnetPath)
+{
+    // Errors while reading from the file shouldn't throw unless
+    // file.exception(bits) is set
+    std::ifstream file(dotnetPath, std::ios::binary);
+    if (!file.is_open())
+    {
+        LOG_TRACEF(L"Failed to open file %ls", dotnetPath);
+        return false;
+    }
+
+    // Read the DOS header
+    IMAGE_DOS_HEADER dosHeader{};
+    file.read(reinterpret_cast<char*>(&dosHeader), sizeof(dosHeader));
+    if (dosHeader.e_magic != IMAGE_DOS_SIGNATURE) // 'MZ'
+    {
+        LOG_TRACEF(L"%ls is not a valid executable file (missing MZ header).", dotnetPath);
+        return false;
+    }
+
+    // Seek to the PE header
+    file.seekg(dosHeader.e_lfanew, std::ios::beg);
+
+    // Read the PE header
+    DWORD peSignature{};
+    file.read(reinterpret_cast<char*>(&peSignature), sizeof(peSignature));
+    if (peSignature != IMAGE_NT_SIGNATURE) // 'PE\0\0'
+    {
+        LOG_TRACEF(L"%ls is not a valid PE file (missing PE header).", dotnetPath);
+        return false;
+    }
+
+    // Read the file header
+    IMAGE_FILE_HEADER fileHeader{};
+    file.read(reinterpret_cast<char*>(&fileHeader), sizeof(fileHeader));
+
+    // Read the optional header magic field
+    WORD magic{};
+    file.read(reinterpret_cast<char*>(&magic), sizeof(magic));
+
+    // Determine the architecture based on the magic value
+    if (magic == IMAGE_NT_OPTIONAL_HDR32_MAGIC)
+    {
+        LOG_INFOF(L"%ls is 32-bit", dotnetPath);
+        return false;
+    }
+    else if (magic == IMAGE_NT_OPTIONAL_HDR64_MAGIC)
+    {
+        LOG_INFOF(L"%ls is 64-bit", dotnetPath);
+        return true;
+    }
+
+    LOG_INFOF(L"%ls is unknown architecture %i", dotnetPath, fileHeader.Machine);
+    return false;
+}
+
 std::optional<fs::path>
 HostFxrResolver::GetAbsolutePathToDotnetFromProgramFiles()
 {
diff --git a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.h b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.h
index 519f6df52c97..08ec650aec54 100644
--- a/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.h
+++ b/src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.h
@@ -74,6 +74,8 @@ class HostFxrResolver
         const std::filesystem::path & requestedPath
     );
 
+    static BOOL IsX64(const WCHAR* dotnetPath);
+
     struct LocalFreeDeleter
     {
          void operator ()(_In_ LPWSTR* ptr) const
diff --git a/src/Servers/IIS/build/Build.Lib.Settings b/src/Servers/IIS/build/Build.Lib.Settings
index 0dcba8c2011a..9327eb363771 100644
--- a/src/Servers/IIS/build/Build.Lib.Settings
+++ b/src/Servers/IIS/build/Build.Lib.Settings
@@ -9,7 +9,7 @@
 
   <ItemDefinitionGroup>
     <ClCompile>
-      <SDLCheck>false</SDLCheck>
+      <SDLCheck>true</SDLCheck>
       <PreprocessorDefinitions>_LIB;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <ConformanceMode>true</ConformanceMode>
     </ClCompile>