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Date: Mon, 30 Nov 2015 13:14:31 -0800
From: "H. Peter Anvin" <>
To: Ingo Molnar <>, Andy Lutomirski <>
Cc: Kees Cook <>,
        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

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.


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