Improve SELinux Mode Detection with Enhanced GRUB Fallback Logic

toolkit/tools/pkg/imagecustomizerlib/bootcustomizer.go

@@ -88,14 +88,17 @@ func (b *BootCustomizer) getSELinuxModeFromGrub() (imagecustomizerapi.SELinuxMod
 
 	// Get the SELinux kernel command-line args.
 	if b.isGrubMkconfig {
-		_, args, _, err = GetDefaultGrubFileLinuxArgs(b.defaultGrubFileContent, defaultGrubFileVarNameCmdlineForSELinux)
+		// Check both GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT variables
+		// and merge arguments from both if they exist
+		args, err = GetDefaultGrubFileLinuxArgsFromMultipleVars(b.defaultGrubFileContent)
 		if err != nil {
-			return "", err
+			return "", fmt.Errorf("failed to find SELinux args in grub file (%s):\n%w", installutils.GrubDefFile, err)
 		}
 	} else {
 		args, _, err = getLinuxCommandLineArgs(b.grubCfgContent)
 		if err != nil {
-			return imagecustomizerapi.SELinuxModeDefault, err
+			return imagecustomizerapi.SELinuxModeDefault,
+				fmt.Errorf("failed to parse SELinux args from grub file (%s):\n%w", installutils.GrubCfgFile, err)
 		}
 	}
 

toolkit/tools/pkg/imagecustomizerlib/defaultgrubutils.go

@@ -175,6 +175,46 @@ func GetDefaultGrubFileLinuxArgs(defaultGrubFileContent string, varName defaultG
 	return cmdLineVarAssign, args, insertAt, nil
 }
 
+// GetDefaultGrubFileLinuxArgsFromMultipleVars attempts to get Linux kernel command-line args from both
+// GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT variables. It merges arguments from all found variables,
+// allowing args to be distributed across multiple GRUB variables.
+//
+// Parameters:
+//   - defaultGrubFileContent: The content of the /etc/default/grub file
+//
+// Returns:
+//   - args: The merged list of kernel command-line args from all found variables
+//   - error: Error if parsing fails or no variables are found
+func GetDefaultGrubFileLinuxArgsFromMultipleVars(defaultGrubFileContent string) ([]grubConfigLinuxArg, error) {
+	var allArgs []grubConfigLinuxArg
+	var foundAny bool
+
+	// Check both standard GRUB variables in order of preference from low to high
+	varNames := []defaultGrubFileVarName{
+		defaultGrubFileVarNameCmdlineLinuxDefault, // GRUB_CMDLINE_LINUX_DEFAULT
+		defaultGrubFileVarNameCmdlineLinux,        // GRUB_CMDLINE_LINUX
+	}
+
+	for _, varName := range varNames {
+		_, args, _, err := GetDefaultGrubFileLinuxArgs(defaultGrubFileContent, varName)
+		if err != nil {
+			// Variable not found or parsing error, try next variable
+			continue
+		}
+
+		// Merge the args from this variable
+		allArgs = append(allArgs, args...)
+		foundAny = true
+	}
+
+	if !foundAny {
+		return nil, fmt.Errorf("failed to find any of the specified GRUB variables in %s: %v",
+			installutils.GrubDefFile, varNames)
+	}
+
+	return allArgs, nil
+}
+
 // Takes the string contents of /etc/default/grub file and inserts the provided command-line args.
 func addExtraCommandLineToDefaultGrubFile(defaultGrubFileContent string, extraCommandLine string) (string, error) {
 	cmdLineVarAssign, _, insertAt, err := GetDefaultGrubFileLinuxArgs(defaultGrubFileContent,