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

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Date:	Sun, 29 Nov 2015 09:05:05 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	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>,
	"H. Peter Anvin" <hpa@...or.com>, 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


* 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.

Thanks,

	Ingo
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