Re: Oops caused by race between livepatch and ftrace

[Joe Lawrence]

On 5/20/19 5:19 PM, Joe Lawrence wrote:
> On 5/20/19 5:09 PM, Johannes Erdfelt wrote:
> > On Mon, May 20, 2019, Joe Lawrence <joe.lawrence@xxxxxxxxxx> wrote:
> > > These two testing scenarios might be interesting to add to our selftests
> > > suite.  Can you post or add the source(s) to livepatch-test<n>.ko to the
> > > tarball?
> >
> > I made the livepatches using kpatch-build and this simple patch:
> >
> > diff --git a/fs/proc/version.c b/fs/proc/version.c
> > index 94901e8e700d..6b8a3449f455 100644
> > --- a/fs/proc/version.c
> > +++ b/fs/proc/version.c
> > @@ -12,6 +12,7 @@ static int version_proc_show(struct seq_file *m, void *v)
> >    		utsname()->sysname,
> >    		utsname()->release,
> >    		utsname()->version);
> > +	seq_printf(m, "example livepatch\n");
> >    	return 0;
> >    }
> >
> > I just created enough livepatches with the same source patch so that I
> > could reproduce the issue somewhat reliably.
> >
> > I'll see if I can make something that uses klp directly.
>
> Ah ok great, I was hoping it was a relatively simply livepatch.  We
> could probably reuse lib/livepatch/test_klp_livepatch.c to do this
> (patching cmdline_proc_show instead).
>
> > The rest of the userspace in the initramfs is really straight forward
> > with the only interesting parts being a couple of shell scripts.
>
> Yup.  I'll be on PTO later this week, but I'll see about extracting the
> scripts and building a pile of livepatch .ko's to see how easily it
> reproduces without qemu.

D'oh -- I just remembered that klp doesn't create those klp (arch) 
relocation sections just yet!  Without those, the window for module RO 
-> RW -> RO in klp_init_object_loaded is going to be really small... at 
least I can't reproduce it yet without those special sections.  So maybe 
such selftests need to wait post klp-convert.


BTW, livepatching folks -- speaking of this window, does it make sense 
for klp_init_object_loaded() to unconditionally frob the module section 
permissions?  Should it only bother iff it's going to apply 
relocations/alternatives/paravirt?

-- Joe