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Message-ID: <20180715224446.GA29087@gmail.com>
Date: Mon, 16 Jul 2018 00:44:46 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Alexander Popov <alex.popov@...ux.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
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	Richard Sandiford <richard.sandiford@....com>,
	Thomas Gleixner <tglx@...utronix.de>, Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Dmitry V. Levin" <ldv@...linux.org>,
	Emese Revfy <re.emese@...il.com>, Jonathan Corbet <corbet@....net>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Thomas Garnier <thgarnie@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
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	Dmitry Safonov <dsafonov@...tuozzo.com>,
	Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>,
	Florian Weimer <fweimer@...hat.com>,
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	Andrey Konovalov <andreyknvl@...gle.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v14 0/6] Introduce the STACKLEAK feature and a test for it


* Kees Cook <keescook@...omium.org> wrote:

> On Thu, Jul 12, 2018 at 2:22 PM, Alexander Popov <alex.popov@...ux.com> wrote:
> > On 12.07.2018 23:50, Ingo Molnar wrote:
> >> Let's make sure informed users have an easy runtime way out
> >> from the worst of the overhead that doesn't involve "recompile your distro
> >> kernel". Also, make it easier to measure and fingerpoint the overhead...
> >
> > Would you like the following solution?
> >
> > I'll create the CONFIG_STACKLEAK_RUNTIME_DISABLE config option, which would be
> > similar to CONFIG_SECURITY_SELINUX_DISABLE. That option will provide a sysctl
> > switch disabling stackleak_erase(), which provides the most of performance penalty.
> 
> I don't think CONFIG/sysctl is the way to go. I'd recommend making it
> a boot arg and using a static key, similar to what's happening to
> hardened_usercopy:

Why no sysctl? It's a PITA to reboot systems just to turn a stupid knob off.

Also, it's _much_ easier to measure performance impact when there's a sysctl.

Thanks,

	Ingo

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