From mboxrd@z Thu Jan 1 00:00:00 1970 Sender: Ingo Molnar Date: Thu, 12 Jul 2018 15:59:44 +0200 From: Ingo Molnar Subject: Re: [PATCH v14 0/6] Introduce the STACKLEAK feature and a test for it Message-ID: <20180712135944.GB6199@gmail.com> References: <1531341400-12077-1-git-send-email-alex.popov@linux.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: To: Linus Torvalds Cc: Alexander Popov , Kernel Hardening , Kees Cook , Pax Team , Brad Spengler , Andrew Lutomirski , Tycho Andersen , Laura Abbott , Mark Rutland , Ard Biesheuvel , Borislav Petkov , Richard Sandiford , Thomas Gleixner , Peter Anvin , Peter Zijlstra , "Dmitry V. Levin" , Emese Revfy , Jonathan Corbet , Andrey Ryabinin , "Kirill A. Shutemov" , Thomas Garnier , Andrew Morton , Alexei Starovoitov , Josef Bacik , Masami Hiramatsu , Nick Piggin , Al Viro , David Miller , dingtianhong , David Woodhouse , Josh Poimboeuf , Steven Rostedt , Dominik Brodowski , =?iso-8859-1?Q?J=FCrgen_Gro=DF?= , Greg Kroah-Hartman , Dan Williams , Dave Hansen , Mathias Krause , Vikas Shivappa , Kyle Huey , Dmitry Safonov , Will Deacon , Arnd Bergmann , Florian Weimer , Boris Lukashev , Andrey Konovalov , the arch/x86 maintainers , Linux Kernel Mailing List List-ID: * Linus Torvalds wrote: > On Wed, Jul 11, 2018 at 1:37 PM Alexander Popov 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