Long answer is:
Regarding to this documents:
$session=new CHttpSession;
$session->open();
$value1=$session['name1']; // get session variable 'name1'
$value2=$session['name2']; // get session variable 'name2'
foreach($session as $name=>$value) // traverse all session variables
$session['name3']=$value3; // set session variable 'name3'
You can use as well:
Yii::app()->session->set('hashList', $hashList);
Yii::app()->session->get('hashList');
And set it again.
Beside this session thing, why do not you use this:
$this->render('/process', array('hashValue => $formHash, 'hashList' => $hashList));
So you do not need to save it in a session if you can reach it directly into the view.