node, 133 bytes

Result

AC

Duration

1098ms

Code [DL]

r='repeat';process.stdin.on('data',s=>{[h,w]=(''+s).split('\n'),a='*'[r](w)+'\n',console.log(a+('*'+' '[r](w-2)+'*\n')[r](h-2)+a)});

stdin

23
28

stdout

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

stderr