linux-hardening - Re: [PATCH] sh: machvec: Use char[] for section boundaries

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Message-ID: <20220908221538.GD8773@brightrain.aerifal.cx>
Date:   Thu, 8 Sep 2022 18:15:39 -0400
From:   Rich Felker <dalias@...c.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        linux-sh@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] sh: machvec: Use char[] for section boundaries

On Wed, Sep 07, 2022 at 04:43:45PM -0700, Kees Cook wrote:
> As done for other sections, define the extern as a character array,
> which relaxes many of the compiler-time object size checks, which would
> otherwise assume it's a single long. Solves the following build error:
> 
> arch/sh/kernel/machvec.c: error: array subscript 'struct sh_machine_vector[0]' is partly outside array bounds of 'long int[1]' [-Werror=array-bounds]:  => 105:33

LGMT. This is the approach I recommend for this general type of
mechanism. So,

Acked-by: Rich Felker <dalias@...c.org>

Since I haven't been on top of collating patches for upstreaming, I'd
be happy if anyone else wants to take this in their tree before I get
back to it.

Rich


> Cc: Yoshinori Sato <ysato@...rs.sourceforge.jp>
> Cc: Rich Felker <dalias@...c.org>
> Cc: linux-sh@...r.kernel.org
> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Link: https://lore.kernel.org/lkml/alpine.DEB.2.22.394.2209050944290.964530@ramsan.of.borg/
> Fixes: 9655ad03af2d ("sh: Fixup machvec support.")
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  arch/sh/include/asm/sections.h |  2 +-
>  arch/sh/kernel/machvec.c       | 10 +++++-----
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/sh/include/asm/sections.h b/arch/sh/include/asm/sections.h
> index 8edb824049b9..0cb0ca149ac3 100644
> --- a/arch/sh/include/asm/sections.h
> +++ b/arch/sh/include/asm/sections.h
> @@ -4,7 +4,7 @@
>  
>  #include <asm-generic/sections.h>
>  
> -extern long __machvec_start, __machvec_end;
> +extern char __machvec_start[], __machvec_end[];
>  extern char __uncached_start, __uncached_end;
>  extern char __start_eh_frame[], __stop_eh_frame[];
>  
> diff --git a/arch/sh/kernel/machvec.c b/arch/sh/kernel/machvec.c
> index d606679a211e..57efaf5b82ae 100644
> --- a/arch/sh/kernel/machvec.c
> +++ b/arch/sh/kernel/machvec.c
> @@ -20,8 +20,8 @@
>  #define MV_NAME_SIZE 32
>  
>  #define for_each_mv(mv) \
> -	for ((mv) = (struct sh_machine_vector *)&__machvec_start; \
> -	     (mv) && (unsigned long)(mv) < (unsigned long)&__machvec_end; \
> +	for ((mv) = (struct sh_machine_vector *)__machvec_start; \
> +	     (mv) && (unsigned long)(mv) < (unsigned long)__machvec_end; \
>  	     (mv)++)
>  
>  static struct sh_machine_vector * __init get_mv_byname(const char *name)
> @@ -87,8 +87,8 @@ void __init sh_mv_setup(void)
>  	if (!machvec_selected) {
>  		unsigned long machvec_size;
>  
> -		machvec_size = ((unsigned long)&__machvec_end -
> -				(unsigned long)&__machvec_start);
> +		machvec_size = ((unsigned long)__machvec_end -
> +				(unsigned long)__machvec_start);
>  
>  		/*
>  		 * Sanity check for machvec section alignment. Ensure
> @@ -102,7 +102,7 @@ void __init sh_mv_setup(void)
>  		 * vector (usually the only one) from .machvec.init.
>  		 */
>  		if (machvec_size >= sizeof(struct sh_machine_vector))
> -			sh_mv = *(struct sh_machine_vector *)&__machvec_start;
> +			sh_mv = *(struct sh_machine_vector *)__machvec_start;
>  	}
>  
>  	pr_notice("Booting machvec: %s\n", get_system_type());
> -- 
> 2.34.1