Re: [PATCH bpf-next 2/3] bpf: Add user memory access kfuncs for linux_binprm

[Anastasios Papagiannis <tasos.papagiannnis@gmail.com>]

Thanks for the review!

> Would it be better to handle that case transparently rather than
> requiring introducing a new kfunc / leaving that gap open for NOMMU?

> Either return an error or perform the copy from bprm->page[].

> Unless there's some reason I'm not seeing.

My understanding is that there is currently no way to use these kfuncs
on a NOMMU system. Although CONFIG_BPF_LSM does not directly depend on
CONFIG_MMU, as far as I can tell, no current NOMMU architecture provides
the required support to use them. For this reason even if I write that
code, this cannot be tested.

> It would also be better for portability across NOMMU / CONFIG_MMU
> systems (the exisiting kfunc is never registered, so a program using it
> would be rejected rather than able to handle the error).

As you suggested, I would propose to register those kfuncs
unconditionally, move the ifdefs inside those kfuncs, in the case
of NOMMU return an error (e.g. -EOPNOTSUPP) and allow the programs to
handle those.

Does this sound reasonable?

Thanks,
Anastasios