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

[H. Peter Anvin]

On 11/29/15 00:05, Ingo Molnar wrote:
> 
> * Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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.

	-hpa


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