linux-kernel - Re: [PATCH v2] kaslr: allow kASLR to be default over Hibernation

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Message-ID: <20160414203444.GC3856@amd>
Date:	Thu, 14 Apr 2016 22:34:44 +0200
From:	Pavel Machek <pavel@...x.de>
To:	Kees Cook <keescook@...omium.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	James Morse <james.morse@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Matt Redfearn <matt.redfearn@...tec.com>,
	Yves-Alexis Perez <corsac@...ian.org>,
	Emrah Demir <ed@...sec.com>, Jonathan Corbet <corbet@....net>,
	"x86@...nel.org" <x86@...nel.org>, Len Brown <len.brown@...el.com>,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v2] kaslr: allow kASLR to be default over Hibernation

On Thu 2016-04-14 13:14:07, Kees Cook wrote:
> On Thu, Apr 14, 2016 at 1:01 PM, Pavel Machek <pavel@...x.de> wrote:
> > Hi!
> >
> >> Since kASLR and Hibernation can not currently coexist at runtime
> >> on x86, the default behavior was to disable kASLR by default when
> >> CONFIG_HIBERNATION was present (to retain original behavior).
> >>
> >> The behavior of kASLR on arm64 (and soon MIPS) is to be enabled by
> >> default when selected at build time. Since arm64 Hibernation does not
> >> conflict with kASLR, this fixes the hibernation argument parsing to be
> >> x86-specific. Additionally, since end users want to be able to select
> >> kASLR on x86 by default at build time, create CONFIG_RANDOMIZE_BASE_ON
> >> that is present only on x86.
> >>
> >> Signed-off-by: Kees Cook <keescook@...omium.org>
> >
> > I believe this is bad idea. arm64 shows that kaslr and hibernation can
> > coexist, and hibernation is still useful when your battery runs out.
> 
> What? I'm confused -- this patch leaves the x86 behavior as-is by
> default but allows hibernation to work with arm64. (For example, right
> now, if you boot arm64 with "kaslr" kernel argument, hibernation will
> get needlessly disabled.)

So it is very different from the PATCH v1, still it shares the
subject?

This is the part I don't like:

> >> Since kASLR and Hibernation can not currently coexist at runtime
> >> on x86, the default behavior was to disable kASLR by default when
> >> CONFIG_HIBERNATION was present (to retain original behavior).

Now I notice that it is quite unclear if it actually changes
anything...

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html