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Date: Mon, 30 Nov 2015 13:33:03 -0800
From: Kees Cook <>
To: "H. Peter Anvin" <>
Cc: Ingo Molnar <>, Andy Lutomirski <>, 
	Linus Torvalds <>, PaX Team <>, 
	"" <>, 
	Mathias Krause <>, 
	"" <>, Ingo Molnar <>, 
	Thomas Gleixner <>, x86-ml <>, Arnd Bergmann <>, 
	Michael Ellerman <>, linux-arch <>, 
	Emese Revfy <>
Subject: Re: [PATCH 0/2] introduce post-init read-only memory

On Mon, Nov 30, 2015 at 1:14 PM, H. Peter Anvin <> wrote:
> On 11/29/15 00:05, Ingo Molnar wrote:
>> * Andy Lutomirski <> 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. :)


Kees Cook
Chrome OS & Brillo Security

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