php, 113 bytes

Result

AC

Duration

943ms

Code [DL]

<?php $h=fgets(STDIN)*1;$w=fgets(STDIN);for($y=$h;$y-->0;)echo"*".str_repeat($y>0&&$y<$h-1?" ":"*",$w-2)."*\n"?>

stdin

24
85

stdout

*************************************************************************************
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*                                                                                   *
*************************************************************************************

stderr

PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1
PHP Notice:  A non well formed numeric value encountered in /volume/CODE on line 1