linux-kernel - Re: [RFC PATCH 4/5] mm, slub: make remaining slub

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Message-ID: <202006051407.F7E66272DA@keescook>
Date:   Fri, 5 Jun 2020 14:07:10 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        vinmenon@...eaurora.org, Matthew Garrett <mjg59@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Vijayanand Jitta <vjitta@...eaurora.org>
Subject: Re: [RFC PATCH 4/5] mm, slub: make remaining slub_debug related
 attributes read-only

On Tue, Jun 02, 2020 at 04:15:18PM +0200, Vlastimil Babka wrote:
> SLUB_DEBUG creates several files under /sys/kernel/slab/<cache>/ that can be
> read to check if the respective debugging options are enabled for given cache.
> Some options, namely sanity_checks, trace, and failslab can be also enabled and
> disabled at runtime by writing into the files.
> 
> The runtime toggling is racy. Some options disable __CMPXCHG_DOUBLE when
> enabled, which means that in case of concurrent allocations, some can still use
> __CMPXCHG_DOUBLE and some not, leading to potential corruption. The s->flags
> field is also not updated or checked atomically. The simplest solution is to
> remove the runtime toggling. The extended slub_debug boot parameter syntax
> introduced by earlier patch should allow to fine-tune the debugging
> configuration during boot with same granularity.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook