Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()

[Jessica Yu]

+++ Peter Zijlstra [16/10/19 11:23 +0200]:
> On Wed, Oct 16, 2019 at 08:51:27AM +0200, Miroslav Benes wrote:
> > On Tue, 15 Oct 2019, Joe Lawrence wrote:
> >
> > > On 10/15/19 10:13 AM, Miroslav Benes wrote:
> > > > Yes, it does. klp_module_coming() calls module_disable_ro() on all
> > > > patching modules which patch the coming module in order to call
> > > > apply_relocate_add(). New (patching) code for a module can be relocated
> > > > only when the relevant module is loaded.
> > >
> > > FWIW, would the LPC blue-sky2 model (ie, Steve's suggestion @ plumber's where
> > > livepatches only patch a single object and updates are kept on disk to handle
> > > coming module updates as they are loaded) eliminate those outstanding
> > > relocations and the need to perform this late permission flipping?
> >
> > Yes, it should, but we don't have to wait for it. PeterZ proposed a
> > different solution to this specific issue in
> > https://lore.kernel.org/lkml/20191015141111.GP2359@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> >
> > It should not be a problem to create a live patch module like that and the
> > code in kernel/livepatch/ is almost ready. Something like
> > module_section_disable_ro(mod, section) (and similar for X protection)
> > should be enough. Module reloads would still require juggling with the
> > protections, but I think it is all feasible.
>
> Just had a browse around the module code, and while the section info is
> in load_info, it doesn't get retained for active modules.
>
> So I suppose I'll go add that for KLP enabled things.

Elf section info does get saved for livepatch modules though, see
mod->klp_info. And wouldn't this only be needed for livepatch modules?