Is movq rax, xmm0 buggy in Radare2?
No, it's just not fully implemented in all debuggers yet.
Native Debugger Works!
This instruction works fine using the native debugger. The native debugger is launched with r2 -d yourFileGoesHere. Alternatively, if you are already in r2 looking at the file, but r2 wasn't launched with the -d switch, the file can be ...
I wrote a small utility back in high school to do something similar:
You inject the .note section with the payload and it will modify the ELF entry pointing to the .note section. Afterwards it will jump back to the original entry point.