[IIS] Manually parse exe bitness #61894

BrennanConroy · 2025-05-12T23:41:35Z

GetBinaryTypeW seems to load the exe into executable space which might trigger custom windows policies. Switch to parsing the PE header to find the bitness.

Tested running x64 app on ARM, ARM x64 emulation mode, and x64 machine.
Tested running x86 app on ARM and x64 machine.
Tested with invalid dotnet.exe file and empty dotnet.exe file.

danmoseley · 2025-05-13T18:53:33Z

src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp

+        return true;
+    }
+
+    LOG_INFOF(L"%ls is unknown architecture %i", dotnetPath, fileHeader.Machine);


? include the magic

Magic only really has 3 values. So by default this is the 3rd case so won't have an interesting value to log.

Copilot

Pull Request Overview

This PR switches from using GetBinaryTypeW to manually parsing the PE header, avoiding side effects from loading the executable.

Introduces a new static function IsX64 to determine executable bitness via PE header parsing.
Replaces the GetBinaryTypeW call in InvokeWhereToFindDotnet with a call to IsX64.
Implements detailed PE header checks and logging in HostFxrResolver.cpp.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.h	Declares the new IsX64 method.
src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp	Replaces GetBinaryTypeW with IsX64 and implements PE header parsing for bitness detection.

Copilot · 2025-05-13T21:20:54Z

src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp

+
+    // Read the DOS header
+    IMAGE_DOS_HEADER dosHeader;
+    file.read(reinterpret_cast<char*>(&dosHeader), sizeof(dosHeader));


Consider verifying that the file.read operation successfully read the expected number of bytes for the DOS header to handle cases of incomplete or corrupted files.

Suggested change

file.read(reinterpret_cast<char*>(&dosHeader), sizeof(dosHeader));

if (!file.read(reinterpret_cast<char*>(&dosHeader), sizeof(dosHeader)))

{

LOG_INFOF(L"Failed to read DOS header from %ls", dotnetPath);

return false;

}

Doesn't seem too interesting, worst case there is nothing left to read and dosHeader.e_magic will be zero and not match IMAGE_DOS_SIGNATURE.

Copilot · 2025-05-13T21:20:54Z

src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp

+    }
+
+    // Seek to the PE header
+    file.seekg(dosHeader.e_lfanew, std::ios::beg);


Check the result of file.seekg to ensure that the PE header offset is valid before proceeding with reading the PE header.

Suggested change

file.seekg(dosHeader.e_lfanew, std::ios::beg);

file.seekg(dosHeader.e_lfanew, std::ios::beg);

if (file.fail())

{

LOG_INFOF(L"Failed to seek to PE header in file %ls. Invalid e_lfanew offset: %ld", dotnetPath, dosHeader.e_lfanew);

return false;

}

Same here, not interesting.

Assuming something interesting does happen here, what does the failure mode look like? Does something higher up handle the exception gracefully?

src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp

BrennanConroy · 2025-05-20T17:12:05Z

/backport to release/8.0

github-actions · 2025-05-20T17:12:14Z

Started backporting to release/8.0: https://github.com/dotnet/aspnetcore/actions/runs/15143703516

BrennanConroy · 2025-05-20T17:12:27Z

/backport to release/9.0

github-actions · 2025-05-20T17:12:35Z

Started backporting to release/9.0: https://github.com/dotnet/aspnetcore/actions/runs/15143709929

github-actions · 2025-05-20T17:12:40Z

@BrennanConroy backporting to "release/8.0" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: [IIS] Manually parse exe bitness
Using index info to reconstruct a base tree...
M	src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
Falling back to patching base and 3-way merge...
Auto-merging src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
CONFLICT (content): Merge conflict in src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 [IIS] Manually parse exe bitness
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!

github-actions · 2025-05-20T17:13:01Z

@BrennanConroy backporting to "release/9.0" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: [IIS] Manually parse exe bitness
Using index info to reconstruct a base tree...
M	src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
Falling back to patching base and 3-way merge...
Auto-merging src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
CONFLICT (content): Merge conflict in src/Servers/IIS/AspNetCoreModuleV2/CommonLib/HostFxrResolver.cpp
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 [IIS] Manually parse exe bitness
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!

[IIS] Manually parse exe bitness

3ac72e4

BrennanConroy added feature-iis Includes: IIS, ANCM area-networking Includes servers, yarp, json patch, bedrock, websockets, http client factory, and http abstractions labels May 12, 2025

build-analysis bot mentioned this pull request May 13, 2025

Known Build Error: ProcessBufferedRenderBatches_WritesRenders fails #61807

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danmoseley reviewed May 13, 2025

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BrennanConroy marked this pull request as ready for review May 14, 2025 04:19

BrennanConroy requested review from halter73, JamesNK and mgravell as code owners May 14, 2025 04:19

BrennanConroy requested review from adityamandaleeka, captainsafia and DeagleGross May 14, 2025 04:19

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BrennanConroy mentioned this pull request May 20, 2025

[Known Build Error] Ssl connection could not be established #62008

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BrennanConroy merged commit fc3994f into main May 20, 2025
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BrennanConroy deleted the brecon/iisbitness branch May 20, 2025 03:40

dotnet-policy-service bot added this to the 10.0-preview5 milestone May 20, 2025

BrennanConroy added a commit that referenced this pull request May 20, 2025

[IIS] Manually parse exe bitness (#61894)

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BrennanConroy added a commit that referenced this pull request May 20, 2025

[IIS] Manually parse exe bitness (#61894)

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This was referenced May 20, 2025

[Backport 8.0] [IIS] Manually parse exe bitness (#61894) #62037

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[Backport 9.0] [IIS] Manually parse exe bitness (#61894) #62038

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[IIS] Manually parse exe bitness #61894

[IIS] Manually parse exe bitness #61894

BrennanConroy commented May 12, 2025 •

edited

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-    file.read(reinterpret_cast<char*>(&dosHeader), sizeof(dosHeader));
+    if (!file.read(reinterpret_cast<char*>(&dosHeader), sizeof(dosHeader)))
+    {
+        LOG_INFOF(L"Failed to read DOS header from %ls", dotnetPath);
+        return false;
+    }

[IIS] Manually parse exe bitness #61894

[IIS] Manually parse exe bitness #61894

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BrennanConroy commented May 12, 2025 • edited Loading

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Pull Request Overview

Reviewed Changes

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BrennanConroy commented May 12, 2025 •

edited

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