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

Andy Lutomirski
2015-11-30T21:38:28Z

On Mon, Nov 30, 2015 at 1:33 PM, Kees Cook <keescook@chromium.org> wrote:
> On Mon, Nov 30, 2015 at 1:14 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 11/29/15 00:05, Ingo Molnar wrote:
>>>
>>> * 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.
>>>
>>
>> I think what should do is have a debug option which can be set to "rw",
>> "log" or "oops"; the latter should probably be the default.
>
> Can someone write that patch, and then I will include it in the
> series? I haven't touched fault handler code, and it would be faster
> if someone more familiar with that area did it. :)

I think I can do it in a week or two if no one beats me to it.

--Andy