linux-hardening - Re: [PATCH] sched/core: Do not treat class list boundary markers as arrays

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Date:   Mon, 16 May 2022 22:44:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Christophe de Dinechin <dinechin@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] sched/core: Do not treat class list boundary markers as
 arrays

On Mon, May 16, 2022 at 12:42:41PM -0700, Kees Cook wrote:
> GCC 12 is very sensitive about array checking, and views all negative
> array accesses as unsafe (a not unreasonable position). Avoid the
> warnings about __begin_sched_classes being accessed via negative bounds
> by converting them to the pointers they actually are. Silences this
> warning:

Yeah, this patch is *much* saner, thanks!

> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 8dccb34eb190..3d31ed9d33fa 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2190,8 +2190,8 @@ const struct sched_class name##_sched_class \
>  	__section("__" #name "_sched_class")
>  
>  /* Defined in include/asm-generic/vmlinux.lds.h */
> -extern struct sched_class __begin_sched_classes[];
> -extern struct sched_class __end_sched_classes[];
> +extern struct sched_class *__begin_sched_classes;
> +extern struct sched_class *__end_sched_classes;
>  
>  #define sched_class_highest (__end_sched_classes - 1)
>  #define sched_class_lowest  (__begin_sched_classes - 1)
> -- 
> 2.32.0
>