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Message-ID: <20151129080505.GA23721@gmail.com>
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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