Re: modules: add ro_after_init support

[Jessica Yu]

+++ Kees Cook [21/07/16 16:03 -0700]:
> On Wed, Jun 29, 2016 at 9:56 PM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
> > Jessica Yu <jeyu@xxxxxxxxxx> writes:
> > > +++ Rusty Russell [29/06/16 10:38 +0930]:
> > > > Jessica Yu <jeyu@xxxxxxxxxx> writes:
> > > > > Add ro_after_init support for modules by adding a new page-aligned section
> > > > > in the module layout (after rodata) for ro_after_init data and enabling RO
> > > > > protection for that section after module init runs.
> > > > >
> > > > > Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> > > >
> > > > I would prefer a "bool after_init" flag to module_enable_ro().  It's
> > > > more explicit.
> > >
> > > Sure thing, I was just initially worried about the
> > > module_{enable,disable}_ro() asymmetry. :)
> >
> > Yes, but I think compile-time-analyzable behaviour beats
> > runtime-analyzable behaviour for clarity.
> >
> > > > Exposing the flags via uapi looks like a wart, but it's kind of a
> > > > feature, since we don't *unset* it in any section; userspace may want to
> > > > know about it.
> > >
> > > Hm, I'm still unsure about this. I'm starting to think it might be a
> > > bit overkill to expose SHF_RO_AFTER_INIT through uapi (although that
> > > is where all the other SHF_* flags are defined) SHF_RO_AFTER_INIT
> > > would technically be used only internally in the kernel (i.e. module
> > > loader), and it'd also be considered a non-standard flag, using a bit
> > > from SHF_MASKOS (OS-specific range). What do you think?
> >
> > Some arch *could* use it by setting the flag in a section in their
> > module I think; we don't stop them.  Since the other flags are there,
> > I'd leave it.
> >
> > We don't expose the flags via sysfs, though, so that's the only
> > exposure.
>
> What's the state of this series? I'd love it if the functionality
> could land for v4.8...

Hi Kees,

Sorry for the delay! Have been busier than usual lately. I'll be able
to get v2 out tomorrow.

Thanks!
Jessica