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Date: Mon, 30 Nov 2015 13:33:03 -0800
Message-ID: <CAGXu5jK+5UjQt+YZV_oe286+_5NrsZ7gTyVr-v+R7mF1uHskTg@mail.gmail.com>
Subject: Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory
From: Kees Cook <keescook@chromium.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        PaX Team <pageexec@freemail.hu>,
        "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
        Mathias Krause <minipli@googlemail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        x86-ml <x86@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linux-arch <linux-arch@vger.kernel.org>,
        Emese Revfy <re.emese@gmail.com>
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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. :)

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
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