linux-kernel - Re: [RFC v2] implement SL*B and stack usercopy runtime checks

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Date:	Mon, 18 Jul 2011 16:18:05 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	kernel-hardening@...ts.openwall.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [RFC v2] implement SL*B and stack usercopy runtime checks

On Mon, 18 Jul 2011, Vasiliy Kulikov wrote:

> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3844,6 +3844,40 @@ unsigned int kmem_cache_size(struct kmem_cache *cachep)
>  EXPORT_SYMBOL(kmem_cache_size);
>
>  /*
> + * Returns false if and only if [ptr; ptr+len) touches the slab,
> + * but breaks objects boundaries.  It doesn't check whether the
> + * accessed object is actually allocated.
> + */
> +bool slab_access_ok(const void *ptr, unsigned long len)
> +{
> +	struct page *page;
> +	struct kmem_cache *cachep = NULL;

Why = NULL?

> +	struct slab *slabp;
> +	unsigned int objnr;
> +	unsigned long offset;
> +
> +	if (!len)
> +		return true;
> +	if (!virt_addr_valid(ptr))
> +		return true;
> +	page = virt_to_head_page(ptr);
> +	if (!PageSlab(page))
> +		return true;
> +
> +	cachep = page_get_cache(page);
> +	slabp = page_get_slab(page);
> +	objnr = obj_to_index(cachep, slabp, (void *)ptr);
> +	BUG_ON(objnr >= cachep->num);
> +	offset = (const char *)ptr - obj_offset(cachep) -
> +	    (const char *)index_to_obj(cachep, slabp, objnr);
> +	if (offset <= obj_size(cachep) && len <= obj_size(cachep) - offset)
> +		return true;
> +
> +	return false;
> +}
> +EXPORT_SYMBOL(slab_access_ok);
> +
> +/*
>   * This initializes kmem_list3 or resizes various caches for all nodes.
>   */
>  static int alloc_kmemlist(struct kmem_cache *cachep, gfp_t gfp)

> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2623,6 +2623,34 @@ unsigned int kmem_cache_size(struct kmem_cache *s)
>  }
>  EXPORT_SYMBOL(kmem_cache_size);
>
> +/*
> + * Returns false if and only if [ptr; ptr+len) touches the slab,
> + * but breaks objects boundaries.  It doesn't check whether the
> + * accessed object is actually allocated.
> + */
> +bool slab_access_ok(const void *ptr, unsigned long len)
> +{
> +	struct page *page;
> +	struct kmem_cache *s = NULL;

No need to assign NULL.

> +	unsigned long offset;
> +
> +	if (len == 0)
> +		return true;
> +	if (!virt_addr_valid(ptr))
> +		return true;
> +	page = virt_to_head_page(ptr);
> +	if (!PageSlab(page))
> +		return true;
> +
> +	s = page->slab;
> +	offset = ((const char *)ptr - (const char *)page_address(page)) % s->size;

Are the casts necessary? Both are pointers to void *


> +	if (offset <= s->objsize && len <= s->objsize - offset)

If offset == s->objsize then we access the first byte after the object.
--
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