You can set the smart search to filter out results for pages (documents) that users are not allowed to access:
- Open the Pages application.
- Select the page containing the web part you use to get and display search results (Smart search dialog with results or Smart search results).
- Switch to the Design tab and configure the web part (double-click).
- Enable Check permissions in the Document filter category.
- Click OK.
With the Check permissions property enabled, the search results display pages according to the read permissions of individual users.