linux-kernel - Re: [PATCH] mm: Add additional consistency check

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Message-ID: <20170411164134.GA21171@dhcp22.suse.cz>
Date:   Tue, 11 Apr 2017 18:41:36 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Christoph Lameter <cl@...ux.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: Add additional consistency check

On Tue 11-04-17 11:16:42, Cristopher Lameter wrote:
> On Tue, 11 Apr 2017, Michal Hocko wrote:
> 
> >  static inline void *index_to_obj(struct kmem_cache *cache, struct page *page,
> > @@ -3813,14 +3818,18 @@ void kfree(const void *objp)
> >  {
> >  	struct kmem_cache *c;
> >  	unsigned long flags;
> > +	struct page *page;
> >
> >  	trace_kfree(_RET_IP_, objp);
> >
> >  	if (unlikely(ZERO_OR_NULL_PTR(objp)))
> >  		return;
> > +	page = virt_to_head_page(obj);
> > +	if (CHECK_DATA_CORRUPTION(!PageSlab(page)))
> 
> There is a flag SLAB_DEBUG_OBJECTS that is available for this check.

Which is way too late, at least for the kfree path. page->slab_cache
on anything else than PageSlab is just a garbage. And my understanding
of the patch objective is to stop those from happening.

> Consistency checks are configuraable in the slab allocator.

and they have to be compiled in (at least for SLAB) AFAIR.

-- 
Michal Hocko
SUSE Labs