Port to release/2.0.0: Fix chained hardware exception handling on Unix (#12344) (#12350)

There is an issue when hardware exception occurs while handling another hardware exception. In such case,
the exception unwinding ends up in an infinite loop. It is caused by the kernel reusing the same location
for signal handler context.

The fix is to use a windows style context local variable in the common_signal_handler that contains
the right context - it is the original signal context converted to windows style context.

I've also added regression test for the issue.

Author: janvorli

src/pal/src/exception/seh-unwind.cpp

@@ -266,13 +266,8 @@ BOOL PAL_VirtualUnwind(CONTEXT *context, KNONVOLATILE_CONTEXT_POINTERS *contextP
     // cannot cross on some systems.
     if ((void*)curPc == g_SEHProcessExceptionReturnAddress)
     {
-        ULONG contextFlags = CONTEXT_CONTROL | CONTEXT_INTEGER | CONTEXT_FLOATING_POINT | CONTEXT_EXCEPTION_ACTIVE;
-
-    #if defined(_AMD64_)
-        contextFlags |= CONTEXT_XSTATE;
-    #endif
-        size_t nativeContext = *(size_t*)(CONTEXTGetFP(context) + g_common_signal_handler_context_locvar_offset);
-        CONTEXTFromNativeContext((const native_context_t *)nativeContext, context, contextFlags);
+        CONTEXT* signalContext = (CONTEXT*)(CONTEXTGetFP(context) + g_common_signal_handler_context_locvar_offset);
+        memcpy_s(context, sizeof(CONTEXT), signalContext, sizeof(CONTEXT));
 
         return TRUE;
     }

src/pal/src/exception/signal.cpp

@@ -761,12 +761,13 @@ __attribute__((noinline))
 static bool common_signal_handler(int code, siginfo_t *siginfo, void *sigcontext, int numParams, ...)
 {
     sigset_t signal_set;
+    CONTEXT signalContextRecord;
     CONTEXT *contextRecord;
     EXCEPTION_RECORD *exceptionRecord;
     native_context_t *ucontext;
 
     ucontext = (native_context_t *)sigcontext;
-    g_common_signal_handler_context_locvar_offset = (int)((char*)&ucontext - (char*)__builtin_frame_address(0));
+    g_common_signal_handler_context_locvar_offset = (int)((char*)&signalContextRecord - (char*)__builtin_frame_address(0));
 
     AllocateExceptionRecords(&exceptionRecord, &contextRecord);
 
@@ -809,6 +810,9 @@ static bool common_signal_handler(int code, siginfo_t *siginfo, void *sigcontext
     }
 
     contextRecord->ContextFlags |= CONTEXT_EXCEPTION_ACTIVE;
+
+    memcpy_s(&signalContextRecord, sizeof(CONTEXT), contextRecord, sizeof(CONTEXT));
+
     // The exception object takes ownership of the exceptionRecord and contextRecord
     PAL_SEHException exception(exceptionRecord, contextRecord);
 

tests/src/Regressions/coreclr/GitHub_12224/Test12224.csproj

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
+  <PropertyGroup>
+    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
+    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
+    <SchemaVersion>2.0</SchemaVersion>
+    <ProjectGuid>{9CBB2BDE-E9EF-4F0A-840C-0F80380D4513}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+    <ProjectTypeGuids>{786C830F-07A1-408B-BD7F-6EE04809D6DB};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
+    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\..\</SolutionDir>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <CLRTestKind>BuildAndRun</CLRTestKind>
+    <CLRTestPriority>1</CLRTestPriority>
+  </PropertyGroup>
+  <!-- Default configurations to help VS understand the configurations -->
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
+  </PropertyGroup>
+  <ItemGroup>
+    <CodeAnalysisDependentAssemblyPaths Condition=" '$(VS100COMNTOOLS)' != '' " Include="$(VS100COMNTOOLS)..\IDE\PrivateAssemblies">
+      <Visible>False</Visible>
+    </CodeAnalysisDependentAssemblyPaths>
+  </ItemGroup>
+  <ItemGroup>
+    <!-- Add Compile Object Here -->
+    <Compile Include="test12224.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <Service Include="{82A7F48D-3B50-4B1E-B82E-3ADA8210C358}" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="../../../Common/CoreCLRTestLibrary/CoreCLRTestLibrary.csproj" />
+  </ItemGroup>
+  <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
+  <PropertyGroup Condition=" '$(MsBuildProjectDirOverride)' != '' ">
+  </PropertyGroup>
+</Project>

tests/src/Regressions/coreclr/GitHub_12224/test12224.cs

@@ -0,0 +1,43 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+using System;
+using System.Threading;
+
+public class Test12224
+{    
+    // Regression test for EH getting stuck in an infinite loop when NullReferenceException
+    // happens inside a handler of another NullReferenceException.
+    static void ExecuteTest(object context)
+    {
+        string s = null;
+        try
+        {
+            try
+            {
+                int x = s.Length;
+            }
+            catch (NullReferenceException)
+            {
+                int x = s.Length;
+            }
+        }
+        catch (NullReferenceException)
+        {
+
+        }
+    }
+
+    public static int Main()
+    {
+        Thread thread = new Thread(new ParameterizedThreadStart(Test12224.ExecuteTest));
+        thread.IsBackground = true;
+        thread.Start(null);
+
+        // Give the thread 30 seconds to complete (it should be immediate). If it fails
+        // to complete within that timeout, it has hung.
+        bool terminated = thread.Join(new TimeSpan(0, 0, 30));
+
+        return terminated ? 100 : -1;
+    }
+}