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

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Message-ID: <565CBC37.9090106@zytor.com>
Date:	Mon, 30 Nov 2015 13:14:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Andy Lutomirski <luto@...capital.net>
Cc:	Kees Cook <keescook@...omium.org>,
	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 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.

	-hpa


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