Support for PowerShell CLM (#4923)

* Moving Vsts commands from CLI to dedicated PS script file

---------

Co-authored-by: Tim Brigham <[email protected]>
Co-authored-by: Denis Nikulin <[email protected]>

src/Agent.Sdk/Knob/AgentKnobs.cs

@@ -731,5 +731,11 @@ public class AgentKnobs
             "Show warning message on the OS which is not supported by .NET 8",
             new PipelineFeatureSource("Net8UnsupportedOsWarning"),
             new BuiltInDefaultKnobSource("true"));
+
+        public static readonly Knob UsePSScriptWrapper = new Knob(
+            nameof(UsePSScriptWrapper),
+            "Use PowerShell script wrapper to handle PowerShell ConstrainedLanguage mode.",
+            new PipelineFeatureSource("UsePSScriptWrapper"),
+            new BuiltInDefaultKnobSource("false"));
     }
 }

src/Agent.Worker/Handlers/PowerShell3Handler.cs

@@ -57,11 +57,26 @@ public async Task RunAsync()
             ArgUtil.File(moduleFile, nameof(moduleFile));
 
             // Craft the args to pass to PowerShell.exe.
-            string powerShellExeArgs = StringUtil.Format(
+            string powerShellExeArgs = string.Empty;
+
+            if (AgentKnobs.UsePSScriptWrapper.GetValue(ExecutionContext).AsBoolean())
+            {
+                powerShellExeArgs = StringUtil.Format(
+                @"-NoLogo -Sta -NoProfile -ExecutionPolicy Unrestricted -Command ""{3}"" -VstsSdkPath {0} -DebugOption {1} -ScriptBlockString ""{2}""",
+                StepHost.ResolvePathForStepHost(moduleFile).Replace("'", "''"), // nested within a single-quoted string module file name arg #0 
+                ExecutionContext.Variables.System_Debug == true ? "Continue" : "SilentlyContinue", // system debug status variable arg #1 
+                StepHost.ResolvePathForStepHost(scriptFile).Replace("'", "''''"), // nested within a single-quoted string within a single-quoted string arg #2 
+                Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Bin), "powershell", "Start-AzpTask.ps1") // path to wrapper script arg #3
+                ); // nested within a single-quoted string within a single-quoted string
+            }
+            else
+            {
+                powerShellExeArgs = StringUtil.Format(
                 @"-NoLogo -Sta -NoProfile -NonInteractive -ExecutionPolicy Unrestricted -Command "". ([scriptblock]::Create('if ([Console]::InputEncoding -is [Text.UTF8Encoding] -and [Console]::InputEncoding.GetPreamble().Length -ne 0) {{ [Console]::InputEncoding = New-Object Text.UTF8Encoding $false }} if (!$PSHOME) {{ $null = Get-Item -LiteralPath ''variable:PSHOME'' }} else {{ Import-Module -Name ([System.IO.Path]::Combine($PSHOME, ''Modules\Microsoft.PowerShell.Management\Microsoft.PowerShell.Management.psd1'')) ; Import-Module -Name ([System.IO.Path]::Combine($PSHOME, ''Modules\Microsoft.PowerShell.Utility\Microsoft.PowerShell.Utility.psd1'')) }}')) 2>&1 | ForEach-Object {{ Write-Verbose $_.Exception.Message -Verbose }} ; Import-Module -Name '{0}' -ArgumentList @{{ NonInteractive = $true }} -ErrorAction Stop ; $VerbosePreference = '{1}' ; $DebugPreference = '{1}' ; Invoke-VstsTaskScript -ScriptBlock ([scriptblock]::Create('. ''{2}'''))""",
                 StepHost.ResolvePathForStepHost(moduleFile).Replace("'", "''"), // nested within a single-quoted string
                 ExecutionContext.Variables.System_Debug == true ? "Continue" : "SilentlyContinue",
                 StepHost.ResolvePathForStepHost(scriptFile).Replace("'", "''''")); // nested within a single-quoted string within a single-quoted string
+            }
 
             // Resolve powershell.exe.
             string powerShellExe = "powershell.exe";

src/Misc/layoutbin/powershell/Start-AzpTask.ps1

@@ -0,0 +1,84 @@
+<# 
+A PowerShell script that is used to invoke a VSTS task script. This script is used by the VSTS task runner to invoke the task script.
+This script replaces some legacy stuff in PowerShell3Handler.cs and turns it into a dedicated signed script. 
+since it is parameterized it can be signed and trusted for WDAC and CLM.
+#>
+
+param ( 
+    [Parameter(mandatory = $true)]
+    [string]$VstsSdkPath,
+
+    [Parameter(mandatory = $true)]
+    [string]$DebugOption,
+
+    [Parameter(mandatory = $true)]
+    [string]$ScriptBlockString
+
+)
+
+function Get-ClmStatus {
+    # This is new functionality to detect if we are running in a constrained language mode.
+    # This is only used to display debug data if the device is in CLM mode by default.
+
+    # Create a temp file and add the command which not allowed in constrained language mode.
+    $tempFileGuid = New-Guid | Select-Object -Expand Guid 
+    $tempFile = "$($env:AGENT_TEMPDIRECTORY)\$($tempFileGuid).ps1"
+
+    Write-Output '$null = New-Object -TypeName System.Collections.ArrayList' | Out-File -FilePath $tempFile
+
+    try {
+        . $tempFile
+        $status = "FullLanguage"
+    }
+    catch [System.Management.Automation.PSNotSupportedException] {
+        $status = "ConstrainedLanguage"
+    }
+
+    Remove-Item $tempFile 
+    return $status 
+}
+
+$VerbosePreference = $DebugOption
+$DebugPreference = $DebugOption 
+
+if (!$PSHOME) { 
+    Write-Error -Message "The execution cannot be continued since the PSHOME variable is not defined." -ErrorAction Stop
+}
+
+# Check if the device is in CLM mode by default.
+$clmResults = Get-ClmStatus
+Write-Verbose "PowerShell Language mode: $($clmResults)"
+
+if ([Console]::InputEncoding -is [Text.UTF8Encoding] -and [Console]::InputEncoding.GetPreamble().Length -ne 0) {
+    [Console]::InputEncoding = New-Object Text.UTF8Encoding $false 
+}
+
+Import-Module -Name ([System.IO.Path]::Combine($PSHOME, 'Modules\Microsoft.PowerShell.Management\Microsoft.PowerShell.Management.psd1')) 
+Import-Module -Name ([System.IO.Path]::Combine($PSHOME, 'Modules\Microsoft.PowerShell.Utility\Microsoft.PowerShell.Utility.psd1'))
+
+$importSplat = @{
+    Name        = $VstsSdkPath 
+    ErrorAction = 'Stop'
+}
+
+# Import the module and catch any errors
+try {
+    Import-Module @importSplat     
+}
+catch {
+    Write-Verbose $_.Exception.Message -Verbose 
+    throw $_.Exception
+}
+
+# Now create the task and hand of to the task script
+try {
+    Invoke-VstsTaskScript -ScriptBlock ([scriptblock]::Create( $ScriptBlockString ))
+}
+# We want to add improved error handling here - if the error is "xxx\powershell.ps1 is not recognized as the name of a cmdlet, function, script file, or operable program"
+# 
+catch {
+    Write-Verbose "Invoke-VstsTaskScript -ScriptBlock ([scriptblock]::Create( $ScriptBlockString ))"
+    Write-Verbose $_.Exception.Message -Verbose 
+    throw $_.Exception
+}
+#