# with regex:
my $regex = join '|', @good_words;
if (param('evil') =~ m/\A(?:$re)\z/){
   print "good param\n";
}

# with a hash:
my %whitelist;
@whitelist{@good_words} = (1) x @good_words;
if ($whitelist{param('evil')}){
  print "good param\n";
}