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

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Date:	Mon, 30 Nov 2015 13:33:03 -0800
From:	Kees Cook <keescook@...omium.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	PaX Team <pageexec@...email.hu>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Mathias Krause <minipli@...glemail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Michael Ellerman <mpe@...erman.id.au>,
	linux-arch <linux-arch@...r.kernel.org>,
	Emese Revfy <re.emese@...il.com>
Subject: Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory

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