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Date: Thu, 12 Jul 2018 15:59:44 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Alexander Popov <alex.popov@...ux.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Kees Cook <keescook@...omium.org>, Pax Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>,
Andrew Lutomirski <luto@...nel.org>,
Tycho Andersen <tycho@...ho.ws>, Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Borislav Petkov <bp@...en8.de>,
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>,
Alexei Starovoitov <ast@...nel.org>, Josef Bacik <jbacik@...com>,
Masami Hiramatsu <mhiramat@...nel.org>,
Nick Piggin <npiggin@...il.com>, Al Viro <viro@...iv.linux.org.uk>,
David Miller <davem@...emloft.net>,
dingtianhong <dingtianhong@...wei.com>,
David Woodhouse <dwmw@...zon.co.uk>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Dominik Brodowski <linux@...inikbrodowski.net>,
Jürgen Groß <jgross@...e.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Mathias Krause <minipli@...glemail.com>,
Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
Kyle Huey <me@...ehuey.com>,
Dmitry Safonov <dsafonov@...tuozzo.com>,
Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>,
Florian Weimer <fweimer@...hat.com>,
Boris Lukashev <blukashev@...pervictus.com>,
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
* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Wed, Jul 11, 2018 at 1:37 PM Alexander Popov <alex.popov@...ux.com> wrote:
> >
> > This is the 14th version of the patch series introducing STACKLEAK
> > to the mainline kernel for x86. This version comes with style changes
> > according to the feedback from Ingo Molnar and includes Laura Abbott's
> > modifications of scripts/Makefile.gcc-plugins.
>
> As before, I will repeat that I think 1% on a kernel compile (which
> has almost no actual kernel footprint) is a huge cost, and other -
> more kernel-centric - loads will likely see much worse performance.
>
> And I still think that this is stupid, and peoples time would be
> *much* better spent on plugins that have much lower costs and get
> pretty much the same advanytages (ie the whole "just initialize all
> automatics to zero" thing or similar).
>
> But whatever. I'll just continue to tell people not to use silly
> config options that have a high cost-to-point ratio. If people *want*
> to waste their CPU, that's their problem.
So I agree that it's pretty stupid. Since 95%+ of our users just use what the
distro configured - so at minimum I'd like to see a runtime patching based way
for root to disable it, so that people (who care or who are hurt by it) can
turn the check off - which should be the most expensive part causing much of the 1%
overhead.
Shouldn't be too hard to implement, this is just a checking method called for
every system call that does nothing substantial in 99.99999% of the cases.
Thanks,
Ingo
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