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: [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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