linux-kernel - Re: [PATCH v3] mm, kasan: switch SLUB to stackdepot, enable memory quarantine for SLUB

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Date:	Wed, 15 Jun 2016 19:50:02 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Alexander Potapenko <glider@...gle.com>, <adech.fo@...il.com>,
	<cl@...ux.com>, <dvyukov@...gle.com>, <akpm@...ux-foundation.org>,
	<rostedt@...dmis.org>, <iamjoonsoo.kim@....com>,
	<js1304@...il.com>, <kcc@...gle.com>, <kuthonuzo.luruo@....com>
CC:	<kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] mm, kasan: switch SLUB to stackdepot, enable memory
 quarantine for SLUB



On 06/15/2016 06:26 PM, Alexander Potapenko wrote:
> For KASAN builds:
>  - switch SLUB allocator to using stackdepot instead of storing the
>    allocation/deallocation stacks in the objects;
>  - define SLAB_RED_ZONE, SLAB_POISON, SLAB_STORE_USER to zero,
>    effectively disabling these debug features, as they're redundant in
>    the presence of KASAN;

So, why we forbid these? If user wants to set these, why not? If you don't want it, just don't turn them on, that's it.

And sometimes POISON/REDZONE might be actually useful. KASAN doesn't catch everything,
e.g. corruption may happen in assembly code, or DMA by  some device.


>  - change the freelist hook so that parts of the freelist can be put into
>    the quarantine.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---

...

> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index fb87923..8c75953 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -110,7 +110,7 @@ static inline bool kasan_report_enabled(void)
>  void kasan_report(unsigned long addr, size_t size,
>  		bool is_write, unsigned long ip);
>  
> -#ifdef CONFIG_SLAB
> +#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB)
>  void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache);
>  void quarantine_reduce(void);
>  void quarantine_remove_cache(struct kmem_cache *cache);
> diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c
> index 4973505..89259c2 100644
> --- a/mm/kasan/quarantine.c
> +++ b/mm/kasan/quarantine.c
> @@ -149,7 +149,12 @@ static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
>  
>  	local_irq_save(flags);
>  	alloc_info->state = KASAN_STATE_FREE;
> +#ifdef CONFIG_SLAB
>  	___cache_free(cache, object, _THIS_IP_);
> +#elif defined(CONFIG_SLUB)
> +	do_slab_free(cache, virt_to_head_page(object), object, NULL, 1,
> +		_RET_IP_);
> +#endif

Please, add some simple wrapper instead of this.

>  	local_irq_restore(flags);
>  }
>  


...

> diff --git a/mm/slub.c b/mm/slub.c
> index 825ff45..f023dd4 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -191,7 +191,11 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
>  #define MAX_OBJS_PER_PAGE	32767 /* since page.objects is u15 */
>  
>  /* Internal SLUB flags */
> +#ifndef CONFIG_KASAN
>  #define __OBJECT_POISON		0x80000000UL /* Poison object */
> +#else
> +#define __OBJECT_POISON		0x00000000UL /* Disable object poisoning */
> +#endif
>  #define __CMPXCHG_DOUBLE	0x40000000UL /* Use cmpxchg_double */
>  
>  #ifdef CONFIG_SMP
> @@ -454,10 +458,8 @@ static inline void *restore_red_left(struct kmem_cache *s, void *p)
>   */
>  #if defined(CONFIG_SLUB_DEBUG_ON)
>  static int slub_debug = DEBUG_DEFAULT_FLAGS;
> -#elif defined(CONFIG_KASAN)
> -static int slub_debug = SLAB_STORE_USER;
>  #else
> -static int slub_debug;
> +static int slub_debug = SLAB_STORE_USER;

Huh! So now it is on!? By default, and for everyone!