linux-kernel - Re: [PATCH v2 1/2] mm: Expand CONFIG_SLAB_FREELIST

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Date:   Tue, 4 Aug 2020 19:15:41 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Kees Cook <keescook@...omium.org>, akpm@...ux-foundation.org
Cc:     Roman Gushchin <guro@...com>, Christoph Lameter <cl@...ux.com>,
        Alexander Popov <alex.popov@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, vinmenon@...eaurora.org,
        Matthew Garrett <mjg59@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Vijayanand Jitta <vjitta@...eaurora.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mm: Expand CONFIG_SLAB_FREELIST_HARDENED to
 include SLAB

On 6/25/20 11:55 PM, Kees Cook wrote:
> Include SLAB caches when performing kmem_cache pointer verification. A
> defense against such corruption[1] should be applied to all the
> allocators. With this added, the "SLAB_FREE_CROSS" and "SLAB_FREE_PAGE"
> LKDTM tests now pass on SLAB:
> 
>   lkdtm: Performing direct entry SLAB_FREE_CROSS
>   lkdtm: Attempting cross-cache slab free ...
>   ------------[ cut here ]------------
>   cache_from_obj: Wrong slab cache. lkdtm-heap-b but object is from lkdtm-heap-a
>   WARNING: CPU: 2 PID: 2195 at mm/slab.h:530 kmem_cache_free+0x8d/0x1d0
>   ...
>   lkdtm: Performing direct entry SLAB_FREE_PAGE
>   lkdtm: Attempting non-Slab slab free ...
>   ------------[ cut here ]------------
>   virt_to_cache: Object is not a Slab page!
>   WARNING: CPU: 1 PID: 2202 at mm/slab.h:489 kmem_cache_free+0x196/0x1d0
> 
> Additionally clean up neighboring Kconfig entries for clarity,
> readability, and redundant option removal.
> 
> [1] https://github.com/ThomasKing2014/slides/raw/master/Building%20universal%20Android%20rooting%20with%20a%20type%20confusion%20vulnerability.pdf
> 
> Fixes: 598a0717a816 ("mm/slab: validate cache membership under freelist hardening")
> Signed-off-by: Kees Cook <keescook@...omium.org>

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

> ---
>  init/Kconfig | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index a46aa8f3174d..7542d28c6f61 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1885,9 +1885,8 @@ config SLAB_MERGE_DEFAULT
>  	  command line.
>  
>  config SLAB_FREELIST_RANDOM
> -	default n
> +	bool "Randomize slab freelist"
>  	depends on SLAB || SLUB
> -	bool "SLAB freelist randomization"
>  	help
>  	  Randomizes the freelist order used on creating new pages. This
>  	  security feature reduces the predictability of the kernel slab
> @@ -1895,12 +1894,14 @@ config SLAB_FREELIST_RANDOM
>  
>  config SLAB_FREELIST_HARDENED
>  	bool "Harden slab freelist metadata"
> -	depends on SLUB
> +	depends on SLAB || SLUB
>  	help
>  	  Many kernel heap attacks try to target slab cache metadata and
>  	  other infrastructure. This options makes minor performance
>  	  sacrifices to harden the kernel slab allocator against common
> -	  freelist exploit methods.
> +	  freelist exploit methods. Some slab implementations have more
> +	  sanity-checking than others. This option is most effective with
> +	  CONFIG_SLUB.
>  
>  config SHUFFLE_PAGE_ALLOCATOR
>  	bool "Page allocator randomization"
>