Date: Tue, 22 Dec 2015 10:19:40 -0800 From: Dave Hansen <dave.hansen@...el.com> To: Christoph Lameter <cl@...ux.com> Cc: kernel-hardening@...ts.openwall.com, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Laura Abbott <laura@...bott.name>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org> Subject: Re: [RFC][PATCH 6/7] mm: Add Kconfig option for slab sanitization On 12/22/2015 10:08 AM, Christoph Lameter wrote: > On Tue, 22 Dec 2015, Dave Hansen wrote: >>> Why would you use zeros? The point is just to clear the information right? >>> The regular poisoning does that. >> >> It then allows you to avoid the zeroing at allocation time. > > Well much of the code is expecting a zeroed object from the allocator and > its zeroed at that time. Zeroing makes the object cache hot which is an > important performance aspect. Yes, modifying this behavior has a performance impact. It absolutely needs to be evaluated, and I wouldn't want to speculate too much on how good or bad any of the choices are. Just to reiterate, I think we have 3 real choices here: 1. Zero at alloc, only when __GFP_ZERO (behavior today) 2. Poison at free, also Zero at alloc (when __GFP_ZERO) (this patch's proposed behavior, also what current poisoning does, doubles writes) 3. Zero at free, *don't* Zero at alloc (when __GFP_ZERO) (what I'm suggesting, possibly less perf impact vs. #2)
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