Re: [PATCH 0/7] livepatch,module: Remove .klp.arch and module_disable_ro()

[Jessica Yu]

+++ Miroslav Benes [17/04/20 10:27 +0200]:
> On Thu, 16 Apr 2020, Josh Poimboeuf wrote:
>
> > On Thu, Apr 16, 2020 at 05:31:31PM +0200, Jessica Yu wrote:
> > > > But I still not a fan of the fact that COMING has two different
> > > > "states".  For example, after your patch, when apply_relocate_add() is
> > > > called from klp_module_coming(), it can use memcpy(), but when called
> > > > from klp module init() it has to use text poke.  But both are COMING so
> > > > there's no way to look at the module state to know which can be used.
> > >
> > > This is a good observation, thanks for bringing it up. I agree that we
> > > should strive to be consistent with what the module states mean. In my
> > > head, I think it is easiest to assume/establish the following meanings
> > > for each module state:
> > >
> > > MODULE_STATE_UNFORMED - no protections. relocations, alternatives,
> > > ftrace module initialization, etc. any other text modifications are
> > > in the process of being applied. Direct writes are permissible.
> > >
> > > MODULE_STATE_COMING - module fully formed, text modifications are
> > > done, protections applied, module is ready to execute init or is
> > > executing init.
> > >
> > > I wonder if we could enforce the meaning of these two states more
> > > consistently without needing to add another module state.
> > >
> > > Regarding Peter's patches, with the set_all_modules_text_*() api gone,
> > > and ftrace reliance on MODULE_STATE_COMING gone (I think?), is there
> > > anything preventing ftrace_module_init+enable from being called
> > > earlier (i.e., before complete_formation()) while the module is
> > > unformed? Then you don't have to move module_enable_ro/nx later and we
> > > keep the MODULE_STATE_COMING semantics. And if we're enforcing the
> > > above module state meanings, I would also be OK with moving jump_label
> > > and static_call out of the coming notifier chain and making them
> > > explicit calls while the module is still writable.
> > >
> > > Sorry in advance if I missed anything above, I'm still trying to wrap
> > > my head around which callers need what module state and what module
> > > permissions :/
> >
> > Sounds reasonable to me...
> >
> > BTW, instead of hard-coding the jump-label/static-call/ftrace calls, we
> > could instead call notifiers with MODULE_STATE_UNFORMED.
>
> That was exactly what I was thinking about too while reading Jessica's
> email. Since (hopefully all if I remember correctly. I checked only
> random subset now) existing module notifiers check module state,
> it should not be a problem.

Agreed, especially with the growing number of callers now that want to
access the module while it is still writable, it seems reasonable.
IIRC, the module notifiers I looked at too checked the module state
value appropriately, so I think we are fine as well (thanks for checking!)

Jessica