Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory

Ingo Molnar
2015-11-29T08:05:12Z

* Andy Lutomirski <luto@amacapital.net> wrote:

> >> - print a warning and a backtrace, and just mark the page read-write
> >> so that the machine survives, but we get notified and can fix whatever
> >> broken code
> >
> > This seems very easy to add. Should I basically reverse the effects of
> > mark_rodata_ro(), or should I only make the new ro-after-init section as RW?
> > (I think the former would be easier.)
>
> I'd suggest verifying that the page in question is .data..ro_after_init and, if
> so, marking that one page RW.

Yes, this was PaX's suggestion as well, and I agree: doing that turns a quite
possibly unrecoverable boot/shutdown time or suspend/resume time (suspend is
really a special category of 'bootup') crasher oops into a more informative stack
dump.

These ro related faults tend to trigger when init/deinit is running, and oopsing
in those sequences is typically a lot less survivable than say oopsing in a high
level system call while not holding locks.

Thanks,

Ingo