linux-kernel - Re: [PATCH] kexec_file: Adjust type of kexec

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Date:   Tue, 09 May 2017 19:13:45 -0400
From:   Daniel Micay <danielmicay@...il.com>
To:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc:     Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org
Subject: Re: [PATCH] kexec_file: Adjust type of kexec_purgatory

On Tue, 2017-05-09 at 16:06 -0700, Kees Cook wrote:
> Defining kexec_purgatory as a zero-length char array upsets compile
> time size checking. Since this is entirely runtime sized, switch
> this to void *. This silences the warning generated by the future
> CONFIG_FORTIFY_SOURCE, which did not like the memcmp() of a "0 byte"
> array.
> 
> Cc: Daniel Micay <danielmicay@...il.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  kernel/kexec_file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index b118735fea9d..bc86f85f1329 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -30,7 +30,7 @@
>   * Declare these symbols weak so that if architecture provides a
> purgatory,
>   * these will be overridden.
>   */
> -char __weak kexec_purgatory[0];
> +void * __weak kexec_purgatory;
>  size_t __weak kexec_purgatory_size = 0;
>  
>  static int kexec_calculate_store_digests(struct kimage *image);
> -- 
> 2.7.4

It seems more correct to use char `char __weak kexec_purgatory[]`,
otherwise isn't __builtin_object_size ending up as 8, which is still
wrong?