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Date: Fri, 17 May 2019 10:34:26 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Kees Cook <keescook@...omium.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>, Nick Desaulniers <ndesaulniers@...gle.com>,
Kostya Serebryany <kcc@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Sandeep Patil <sspatil@...roid.com>,
Laura Abbott <labbott@...hat.com>, Randy Dunlap <rdunlap@...radead.org>, Jann Horn <jannh@...gle.com>,
Mark Rutland <mark.rutland@....com>, Linux Memory Management List <linux-mm@...ck.org>,
linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 5/4] mm: Introduce SLAB_NO_FREE_INIT and mark excluded caches
On Fri, May 17, 2019 at 2:50 AM Kees Cook <keescook@...omium.org> wrote:
>
> In order to improve the init_on_free performance, some frequently
> freed caches with less sensitive contents can be excluded from the
> init_on_free behavior.
Did you see any notable performance improvement with this patch?
A similar one gave me only 1-2% on the parallel Linux build.
> This patch is modified from Brad Spengler/PaX Team's 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.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> fs/buffer.c | 2 +-
> fs/dcache.c | 3 ++-
> include/linux/slab.h | 3 +++
> kernel/fork.c | 6 ++++--
> mm/rmap.c | 5 +++--
> mm/slab.h | 5 +++--
> net/core/skbuff.c | 6 ++++--
> 7 files changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index 0faa41fb4c88..04a85bd4cf2e 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3457,7 +3457,7 @@ 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_FREE_INIT),
> NULL);
>
> /*
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 8136bda27a1f..323b039accba 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -3139,7 +3139,8 @@ void __init vfs_caches_init_early(void)
> void __init vfs_caches_init(void)
> {
> names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
> + SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_NO_FREE_INIT, 0,
> + PATH_MAX, NULL);
>
> dcache_init();
> inode_init();
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 9449b19c5f10..7eba9ad8830d 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -92,6 +92,9 @@
> /* Avoid kmemleak tracing */
> #define SLAB_NOLEAKTRACE ((slab_flags_t __force)0x00800000U)
>
> +/* Exclude slab from zero-on-free when init_on_free is enabled */
> +#define SLAB_NO_FREE_INIT ((slab_flags_t __force)0x01000000U)
> +
> /* Fault injection mark */
> #ifdef CONFIG_FAILSLAB
> # define SLAB_FAILSLAB ((slab_flags_t __force)0x02000000U)
> diff --git a/kernel/fork.c b/kernel/fork.c
> index b4cba953040a..9868585f5520 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -2550,11 +2550,13 @@ void __init proc_caches_init(void)
>
> mm_cachep = kmem_cache_create_usercopy("mm_struct",
> mm_size, ARCH_MIN_MMSTRUCT_ALIGN,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT,
> + SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT|
> + SLAB_NO_FREE_INIT,
> offsetof(struct mm_struct, saved_auxv),
> sizeof_field(struct mm_struct, saved_auxv),
> NULL);
> - vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
> + vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT|
> + SLAB_NO_FREE_INIT);
> mmap_init();
> nsproxy_cache_init();
> }
> diff --git a/mm/rmap.c b/mm/rmap.c
> index e5dfe2ae6b0d..b7b8013eeb0a 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -432,10 +432,11 @@ 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_TYPESAFE_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT,
> + 0, SLAB_TYPESAFE_BY_RCU|SLAB_PANIC|SLAB_ACCOUNT|
> + SLAB_NO_FREE_INIT,
> anon_vma_ctor);
> anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain,
> - SLAB_PANIC|SLAB_ACCOUNT);
> + SLAB_PANIC|SLAB_ACCOUNT|SLAB_NO_FREE_INIT);
> }
>
> /*
> diff --git a/mm/slab.h b/mm/slab.h
> index 24ae887359b8..f95b4f03c57b 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -129,7 +129,8 @@ static inline slab_flags_t kmem_cache_flags(unsigned int object_size,
> /* Legal flag mask for kmem_cache_create(), for various configurations */
> #define SLAB_CORE_FLAGS (SLAB_HWCACHE_ALIGN | SLAB_CACHE_DMA | \
> SLAB_CACHE_DMA32 | SLAB_PANIC | \
> - SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS )
> + SLAB_TYPESAFE_BY_RCU | SLAB_DEBUG_OBJECTS | \
> + SLAB_NO_FREE_INIT)
>
> #if defined(CONFIG_DEBUG_SLAB)
> #define SLAB_DEBUG_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)
> @@ -535,7 +536,7 @@ static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
> static inline bool slab_want_init_on_free(struct kmem_cache *c)
> {
> if (static_branch_unlikely(&init_on_free))
> - return !(c->ctor);
> + return !(c->ctor) && ((c->flags & SLAB_NO_FREE_INIT) == 0);
> else
> return false;
> }
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index e89be6282693..b65902d2c042 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -3981,14 +3981,16 @@ void __init skb_init(void)
> skbuff_head_cache = kmem_cache_create_usercopy("skbuff_head_cache",
> sizeof(struct sk_buff),
> 0,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC,
> + SLAB_HWCACHE_ALIGN|SLAB_PANIC|
> + SLAB_NO_FREE_INIT,
> offsetof(struct sk_buff, cb),
> sizeof_field(struct sk_buff, cb),
> NULL);
> skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache",
> sizeof(struct sk_buff_fclones),
> 0,
> - SLAB_HWCACHE_ALIGN|SLAB_PANIC,
> + SLAB_HWCACHE_ALIGN|SLAB_PANIC|
> + SLAB_NO_FREE_INIT,
> NULL);
> skb_extensions_init();
> }
> --
> 2.17.1
>
>
> --
> Kees Cook
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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