Re: [kernel-hardening] [PATCH 17/23] dcache: define usercopy region in dentry_cache slab cache

[Eric Biggers]

On Mon, Jun 19, 2017 at 04:36:31PM -0700, Kees Cook wrote:
> From: David Windsor <dave@xxxxxxxxxxxx>
> 
> When a dentry name is short enough, it can be stored directly in
> the dentry itself.  These dentry short names, stored in struct
> dentry.d_iname and therefore contained in the dentry_cache slab cache,
> need to be coped to/from userspace.
> 
> In support of usercopy hardening, this patch defines a region in
> the dentry_cache slab cache in which userspace copy operations
> are allowed.
> 
> This region is known as the slab cache's usercopy region.  Slab
> caches can now check that each copy operation involving cache-managed
> memory falls entirely within the slab's usercopy region.
> 
> This patch is modified from Brad Spengler/PaX Team's PAX_USERCOPY
> whitelisting code in the last public patch of grsecurity/PaX based on my
> understanding of the code. Changes or omissions from the original code are
> mine and don't reflect the original grsecurity/PaX code.
> 

For all these patches please mention *where* the data is being copied to/from
userspace.

> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index a48f54238273..97f4a0117b3b 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -151,6 +151,11 @@ void memcg_destroy_kmem_caches(struct mem_cgroup *);
>  		sizeof(struct __struct), __alignof__(struct __struct),\
>  		(__flags), NULL)
>  
> +#define KMEM_CACHE_USERCOPY(__struct, __flags, __field) kmem_cache_create_usercopy(#__struct,\
> +		sizeof(struct __struct), __alignof__(struct __struct),\
> +		(__flags), offsetof(struct __struct, __field),\
> +		sizeof_field(struct __struct, __field), NULL)
> +

This helper macro should be added in the patch which adds
kmem_cache_create_usercopy(), not in this one.

- Eric