linux-hardening - Re: [PATCH] mm/slab: remove HAVE_HARDENED_USERCOPY

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Date:   Tue, 23 May 2023 08:42:21 +0100
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
        linux-hardening@...r.kernel.org, patches@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/slab: remove HAVE_HARDENED_USERCOPY_ALLOCATOR

On Tue, May 23, 2023 at 09:31:36AM +0200, Vlastimil Babka wrote:
> With SLOB removed, both remaining allocators support hardened usercopy,
> so remove the config and associated #ifdef.
>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  mm/Kconfig       | 2 --
>  mm/slab.h        | 9 ---------
>  security/Kconfig | 8 --------
>  3 files changed, 19 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 7672a22647b4..041f0da42f2b 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -221,7 +221,6 @@ choice
>  config SLAB
>  	bool "SLAB"
>  	depends on !PREEMPT_RT
> -	select HAVE_HARDENED_USERCOPY_ALLOCATOR
>  	help
>  	  The regular slab allocator that is established and known to work
>  	  well in all environments. It organizes cache hot objects in
> @@ -229,7 +228,6 @@ config SLAB
>
>  config SLUB
>  	bool "SLUB (Unqueued Allocator)"
> -	select HAVE_HARDENED_USERCOPY_ALLOCATOR
>  	help
>  	   SLUB is a slab allocator that minimizes cache line usage
>  	   instead of managing queues of cached objects (SLAB approach).
> diff --git a/mm/slab.h b/mm/slab.h
> index f01ac256a8f5..695ef96b4b5b 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -832,17 +832,8 @@ struct kmem_obj_info {
>  void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab);
>  #endif
>
> -#ifdef CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR
>  void __check_heap_object(const void *ptr, unsigned long n,
>  			 const struct slab *slab, bool to_user);
> -#else
> -static inline
> -void __check_heap_object(const void *ptr, unsigned long n,
> -			 const struct slab *slab, bool to_user)
> -{
> -}
> -#endif

Hm, this is still defined in slab.c/slub.c and invoked in usercopy.c, do we
not want the prototype? Perhaps replacing with #ifdef
CONFIG_HARDENED_USERCOPY instead? I may be missing something here :)

> -
>  #ifdef CONFIG_SLUB_DEBUG
>  void skip_orig_size_check(struct kmem_cache *s, const void *object);
>  #endif
> diff --git a/security/Kconfig b/security/Kconfig
> index 97abeb9b9a19..52c9af08ad35 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -127,16 +127,8 @@ config LSM_MMAP_MIN_ADDR
>  	  this low address space will need the permission specific to the
>  	  systems running LSM.
>
> -config HAVE_HARDENED_USERCOPY_ALLOCATOR
> -	bool
> -	help
> -	  The heap allocator implements __check_heap_object() for
> -	  validating memory ranges against heap object sizes in
> -	  support of CONFIG_HARDENED_USERCOPY.
> -
>  config HARDENED_USERCOPY
>  	bool "Harden memory copies between kernel and userspace"
> -	depends on HAVE_HARDENED_USERCOPY_ALLOCATOR
>  	imply STRICT_DEVMEM
>  	help
>  	  This option checks for obviously wrong memory regions when
> --
> 2.40.1
>