If you encrypt your Linux partition you are almost sure to be safe. I say almost, because there could be an attack vector where the BIOS is changed, but that's

If you encrypt your Linux partition you are almost sure to be safe. I say almost, because there could be an attack vector where the BIOS is changed, but that's very unlikely. If you don't encrypt your Linux disk (which you should), you're still very likely safe. It's possible but unlikely that the backdoor would check for a Linux partition and then install an extra backdoor on the Linux side.