Re: [PATCH] kexec_file: Adjust type of kexec_purgatory

From: Daniel Micay
Date: Tue May 09 2017 - 19:13:52 EST


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@xxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> 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?