Re: [PATCH 2/2] kernel: add support for live patching

From: Seth Jennings
Date: Fri Nov 07 2014 - 14:52:45 EST


On Fri, Nov 07, 2014 at 11:40:38AM -0800, Andy Lutomirski wrote:
> On 11/06/2014 06:39 AM, Seth Jennings wrote:
> > This commit introduces code for the live patching core. It implements
> > an ftrace-based mechanism and kernel interface for doing live patching
> > of kernel and kernel module functions.
> >
> > It represents the greatest common functionality set between kpatch and
> > kgraft and can accept patches built using either method.
> >
> > This first version does not implement any consistency mechanism that
> > ensures that old and new code do not run together. In practice, ~90% of
> > CVEs are safe to apply in this way, since they simply add a conditional
> > check. However, any function change that can not execute safely with
> > the old version of the function can _not_ be safely applied in this
> > version.
> >
>
> [...]
>
> > +/********************************************
> > + * Sysfs Interface
> > + *******************************************/
> > +/*
> > + * /sys/kernel/livepatch
> > + * /sys/kernel/livepatch/<patch>
> > + * /sys/kernel/livepatch/<patch>/enabled
> > + * /sys/kernel/livepatch/<patch>/<object>
> > + * /sys/kernel/livepatch/<patch>/<object>/<func>
> > + * /sys/kernel/livepatch/<patch>/<object>/<func>/new_addr
> > + * /sys/kernel/livepatch/<patch>/<object>/<func>/old_addr
> > + */
>
> Letting anyone read new_addr and old_addr is a kASLR leak, and I would
> argue that showing this information to non-root at all is probably a bad
> idea.

Also worth noting that this live patching implementation currently
doesn't support kASLR, as there is a method for the patch module to
supply the old_addr, determined at generation time by pulling from
vmlinux/System.map/etc, for a particular function to resolve symbol
ambiguity in a kallsyms lookup. Obviously, this old_addr would be wrong
for a kernel using kASLR.

Thanks,
Seth

>
> Can you make new_addr and old_addr have mode 0600 and
> /sys/kernel/livepatch itself have mode 0500? For the latter, an admin
> who wants unprivileged users to be able to see it can easily chmod it.
>
> --Andy
> --
> To unsubscribe from this list: send the line "unsubscribe live-patching" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/