It sounds like this is a simple permissions issue with the .elf file on the SD card.
I think by default, any file written to the SD card (especially if it is FAT32 format) is by default set without the executable permission set on it.
You can change the permissions to executable for all users with the following command:
chmod ugo+x hello_world.elf
After that, you should be able to execute the application on your system. If you are interested in learning more about Linux file permissions, there are several good resources available to you like this one: