linux-hardening - Re: [PATCH v5 2/6] mm/slab: Plumb kmem_buckets into __do_kmalloc

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Message-ID: <202406201144.289A1A14@keescook>
Date: Thu, 20 Jun 2024 11:46:42 -0700
From: Kees Cook <kees@...nel.org>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: "GONG, Ruiqi" <gongruiqi@...weicloud.com>,
	Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	jvoisin <julien.voisin@...tri.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>,
	Xiu Jianfeng <xiujianfeng@...wei.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Jann Horn <jannh@...gle.com>, Matteo Rizzo <matteorizzo@...gle.com>,
	Thomas Graf <tgraf@...g.ch>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-hardening@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v5 2/6] mm/slab: Plumb kmem_buckets into
 __do_kmalloc_node()

On Thu, Jun 20, 2024 at 03:37:31PM +0200, Vlastimil Babka wrote:
> On 6/20/24 3:08 PM, Vlastimil Babka wrote:
> > On 6/19/24 9:33 PM, Kees Cook wrote:
> > I was wondering why I don't see the buckets in slabinfo and turns out it was
> > SLAB_MERGE_DEFAULT. It would probably make sense for SLAB_MERGE_DEFAULT to
> > depends on !SLAB_BUCKETS now as the merging defeats the purpose, wdyt?
> 
> Hm I might have been just blind, can see them there now. Anyway it probably
> doesn't make much sense to have SLAB_BUCKETS and/or RANDOM_KMALLOC_CACHES
> together with SLAB_MERGE_DEFAULT?

It's already handled so that the _other_ caches can still be merged if
people want it. See new_kmalloc_cache():

#ifdef CONFIG_RANDOM_KMALLOC_CACHES
        if (type >= KMALLOC_RANDOM_START && type <= KMALLOC_RANDOM_END)
                flags |= SLAB_NO_MERGE;
#endif

-- 
Kees Cook