linux-kernel - Re: [PATCH v2] Introduce sysfs interface to disable kfence for selected slabs.

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Message-ID: <c60897e7-fa5d-a1a9-09a6-c80cfe4b5fd5@suse.cz>
Date:   Fri, 12 Aug 2022 12:28:53 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Imran Khan <imran.f.khan@...cle.com>, glider@...gle.com,
        elver@...gle.com, dvyukov@...gle.com, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, roman.gushchin@...ux.dev,
        42.hyeyoo@...il.com
Cc:     linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org
Subject: Re: [PATCH v2] Introduce sysfs interface to disable kfence for
 selected slabs.

On 8/11/22 10:59, Imran Khan wrote:
> By default kfence allocation can happen for any slab object, whose size
> is up to PAGE_SIZE, as long as that allocation is the first allocation
> after expiration of kfence sample interval. But in certain debugging
> scenarios we may be interested in debugging corruptions involving
> some specific slub objects like dentry or ext4_* etc. In such cases
> limiting kfence for allocations involving only specific slub objects
> will increase the probablity of catching the issue since kfence pool
> will not be consumed by other slab objects.
> 
> This patch introduces a sysfs interface '/sys/kernel/slab/<name>/skip_kfence'
> to disable kfence for specific slabs. Having the interface work in this
> way does not impact current/default behavior of kfence and allows us to
> use kfence for specific slabs (when needed) as well. The decision to
> skip/use kfence is taken depending on whether kmem_cache.flags has
> (newly introduced) SLAB_SKIP_KFENCE flag set or not.
> 
> Signed-off-by: Imran Khan <imran.f.khan@...cle.com>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

Nit below:

> ---
> 
> Changes since v1:
>  - Remove RFC tag
> 
>  include/linux/slab.h |  6 ++++++
>  mm/kfence/core.c     |  7 +++++++
>  mm/slub.c            | 27 +++++++++++++++++++++++++++
>  3 files changed, 40 insertions(+)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 0fefdf528e0d..947d912fd08c 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -119,6 +119,12 @@
>   */
>  #define SLAB_NO_USER_FLAGS	((slab_flags_t __force)0x10000000U)
>  
> +#ifdef CONFIG_KFENCE
> +#define SLAB_SKIP_KFENCE            ((slab_flags_t __force)0x20000000U)
> +#else
> +#define SLAB_SKIP_KFENCE            0
> +#endif

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