kernel modules, derived work and GPLv2

[Phil Perry]

Hello list,

I am seeking to fully understand my obligations under the GPL regarding 
kernel modules, derived works and requirements to distribute the source 
code.

If I build a kernel module (driver) against the linux kernel, and that 
kernel module is deemed to be a derived work, I understand that it must 
also be licensed under the GPL. As such, if I distribute the binary 
kernel module (driver), I must also distribute the kernel module source 
code. That all seems straightforward, no issues there.

However, what about the source code for the linux kernel the kernel 
module (driver) was built against - is that also deemed part of the 
derived work and must I also distribute the linux kernel source code 
against which my binary kernel module (driver) was compiled?

If yes, what part of the linux kernel source code tree must I 
distribute? All of it, or just the source code for the interfaces 
(exported symbols) I have used in my module?

If my question is not appropriate for this list, I will happily accept 
pointers to a more appropriate forum.

Thanks,

Phil