Date: Fri, 26 Feb 2016 14:33:17 -0800 From: Kees Cook <keescook@...omium.org> To: Laura Abbott <labbott@...hat.com> Cc: Laura Abbott <labbott@...oraproject.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCHv2] lkdtm: Add READ_AFTER_FREE test On Fri, Feb 26, 2016 at 2:19 PM, Laura Abbott <labbott@...hat.com> wrote: > I did a quick hack of zero poisoning for the slab allocator and I > didn't see any improvement in hackbench performance which is fairly > sensitive to slab performance. This doesn't surprise me when I > actually think about it. > > Before I sent out my last set of performance optimizations for > SLUB debug path, I did a profile with ftrace to see if there was > anything else quick I could do. My profiling showed that the > poisoning itself was not where most of the allocation time was > spent. 25-50% of the time was being spent in removing the CPU slab. > Considering poisoning means that the CPU slab is never really used, > this can probably be improved. It's worth noting that the > PAX_MEMORY_SANITIZE implementation still uses the fast path so it > isn't affected here. (The trade off is a minor penalty on the > fast path even when poisoning is disabled which isn't acceptable > to the maintainers currently.) Oh right, all of this is still the slow path... > Basically, until we've optimized other things I don't think the > zero poisoning will have a significant effect on performance. > The next set of optimizations will involve changing some of the > guts of the SLUB allocator. I have some ideas how to approach this > but we'll see if they pan out. And we can't just have a CONFIG for the fast-path sanitization? Then it's not in anyone's way, etc? -Kees -- Kees Cook Chrome OS & Brillo Security
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