Date: Tue, 22 Dec 2015 19:37:40 +0100 From: Mathias Krause <minipli@...glemail.com> To: Laura Abbott <laura@...bott.name> Cc: kernel-hardening@...ts.openwall.com, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, "linux-kernel@...r.kernel.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 22 December 2015 at 18:51, Laura Abbott <laura@...bott.name> wrote: >> [snip] >> >> Related to this, have you checked that the sanitization doesn't >> interfere with the various slab handling schemes, namely RCU related >> specialties? Not all caches are marked SLAB_DESTROY_BY_RCU, some use >> call_rcu() instead, implicitly relying on the semantics RCU'ed slabs >> permit, namely allowing a "use-after-free" access to be legitimate >> within the RCU grace period. Scrubbing the object during that period >> would break that assumption. > > > I haven't looked into that. I was working off the assumption that > if the regular SLAB debug poisoning worked so would the sanitization. > The regular debug poisoning only checks for SLAB_DESTROY_BY_RCU so > how does that work then? Maybe it doesn't? ;) How many systems, do you think, are running with enabled DEBUG_SLAB / SLUB_DEBUG in production? Not so many, I'd guess. And the ones running into issues probably just disable DEBUG_SLAB / SLUB_DEBUG. Btw, SLUB not only looks for SLAB_DESTROY_BY_RCU but also excludes "call_rcu slabs" via other mechanisms. As SLUB is the default SLAB allocator for quite some time now, even with enabled SLUB_DEBUG one wouldn't be able to trigger RCU related sanitization issues. >> Speaking of RCU, do you have a plan to support RCU'ed slabs as well? >> > > My only plan was to get the base support in. I didn't have a plan to > support RCU slabs but that's certainly something to be done in the > future. "Base support", in my opinion, includes covering the buddy allocator as well. Otherwise this feature is incomplete. Regards, Mathias
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