[kernel-hardening] Re: [RFC][PATCH 5/7] mm: Mark several cases as SLAB_NO_SANITIZE

Kees Cook
2016-01-06T00:21:56Z

On Mon, Dec 21, 2015 at 7:40 PM, Laura Abbott <laura@labbott.name> wrote:
>
> Sanitization is useful for security but comes at the cost of performance
> in clearing on free. Mark select caches as SLAB_NO_SANITIZE so
> sanitization will not happen under the default configuration. The

Can you describe why these were selected?

> kernel may be booted with the proper command line option to allow these
> caches to be sanitized.

Might be good to specifically mention the command line used to
sanitize even these caches.

-Kees

>
> All credit for the original work should be given to Brad Spengler and
> the PaX Team.
>
> Signed-off-by: Laura Abbott <laura@labbott.name>
> ---
> This is the initial set of excludes that the grsecurity patches had.
> More may need to be added/removed as the series is tested.
> ---
> fs/buffer.c | 2 +-
> fs/dcache.c | 2 +-
> kernel/fork.c | 2 +-
> mm/rmap.c | 4 ++--
> mm/slab.h | 2 +-
> net/core/skbuff.c | 16 ++++++++--------
> 6 files changed, 14 insertions(+), 14 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 4f4cd95..f19e4ab 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3417,7 +3417,7 @@ void __init buffer_init(void)
> bh_cachep = kmem_cache_create("buffer_head",
> sizeof(struct buffer_head), 0,
> (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
> - SLAB_MEM_SPREAD),
> + SLAB_MEM_SPREAD|SLAB_NO_SANITIZE),
> NULL);
>
> /*
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 5c33aeb..470f6be 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -3451,7 +3451,7 @@ void __init vfs_caches_init_early(void)
> void __init vfs_caches_init(void)
> {
> names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
> + SLAB_NO_SANITIZE|SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
>
> dcache_init();
> inode_init();
> diff --git a/kernel/fork.c b/kernel/fork.c
> index fce002e..35db9c3 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1868,7 +1868,7 @@ void __init proc_caches_init(void)
> mm_cachep = kmem_cache_create("mm_struct",
> sizeof(struct mm_struct), ARCH_MIN_MMSTRUCT_ALIGN,
> SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NOTRACK, NULL);
> - vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC);
> + vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_NO_SANITIZE);
> mmap_init();
> nsproxy_cache_init();
> }
> diff --git a/mm/rmap.c b/mm/rmap.c
> index b577fbb..74296d9 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -428,8 +428,8 @@ static void anon_vma_ctor(void *data)
> void __init anon_vma_init(void)
> {
> anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
> - 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
> - anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
> + 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC|SLAB_NO_SANITIZE, anon_vma_ctor);
> + anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC|SLAB_NO_SANITIZE);
> }
>
> /*
> diff --git a/mm/slab.h b/mm/slab.h
> index b54b636..6de99da 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -137,7 +137,7 @@ static inline unsigned long kmem_cache_flags(unsigned long object_size,
>
> /* Legal flag mask for kmem_cache_create(), for various configurations */
> #define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | SLAB_PANIC | \
> - SLAB_DESTROY_BY_RCU | SLAB_DEBUG_OBJECTS )
> + SLAB_DESTROY_BY_RCU | SLAB_DEBUG_OBJECTS | SLAB_NO_SANITIZE)
>
> #if defined(CONFIG_DEBUG_SLAB)
> #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index b2df375..1d499ea 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3316,15 +3316,15 @@ done:
> void __init skb_init(void)
> {
> skbuff_head_cache = kmem_cache_create("skbuff_head_cache",
> - sizeof(struct sk_buff),
> - 0,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC,
> - NULL);
> + sizeof(struct sk_buff),
> + 0,
> + SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NO_SANITIZE,
> + NULL);
> skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache",
> - sizeof(struct sk_buff_fclones),
> - 0,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC,
> - NULL);
> + sizeof(struct sk_buff_fclones),
> + 0,
> + SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NO_SANITIZE,
> + NULL);
> }
>
> /**
> --
> 2.5.0
>

--
Kees Cook
Chrome OS & Brillo Security