linux-hardening - Re: [PATCH v6 2/6] init_on_alloc: Optimize static branches

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Message-ID: <202103151514.AE11A69683@keescook>
Date:   Mon, 15 Mar 2021 15:15:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Popov <alex.popov@...ux.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/6] init_on_alloc: Optimize static branches

On Mon, Mar 15, 2021 at 11:02:25AM -0700, Kees Cook wrote:
> diff --git a/mm/slab.h b/mm/slab.h
> index 076582f58f68..b0977d525c06 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -601,7 +601,8 @@ static inline void cache_random_seq_destroy(struct kmem_cache *cachep) { }
>  
>  static inline bool slab_want_init_on_alloc(gfp_t flags, struct kmem_cache *c)
>  {
> -	if (static_branch_unlikely(&init_on_alloc)) {
> +	if (static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,

Gah, this should be CONFIG_INIT_ON_ALLOC_DEFAULT_ON.

I'll see if there are any more comments before sending a v7...

-Kees

> +				&init_on_alloc)) {
>  		if (c->ctor)
>  			return false;
>  		if (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON))
> @@ -613,7 +614,8 @@ 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))
> +	if (static_branch_maybe(CONFIG_INIT_ON_FREE_DEFAULT_ON,
> +				&init_on_free))
>  		return !(c->ctor ||
>  			 (c->flags & (SLAB_TYPESAFE_BY_RCU | SLAB_POISON)));
>  	return false;
> -- 
> 2.25.1
> 

-- 
Kees Cook