linux-kernel - Re: [PATCH v2] kexec_file: Adjust declaration of kexec

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Date:   Wed, 10 May 2017 15:08:59 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     kexec@...ts.infradead.org, Daniel Micay <danielmicay@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kexec_file: Adjust declaration of kexec_purgatory

Kees Cook <keescook@...omium.org> writes:

> Defining kexec_purgatory as a zero-length char array upsets compile
> time size checking. Since this is built on a per-arch basis, define
> it as an unsized char array (like is done for other similar things,
> e.g. linker sections). This silences the warning generated by the future
> CONFIG_FORTIFY_SOURCE, which did not like the memcmp() of a "0 byte"
> array. This drops the __weak and uses an extern instead, since both
> users define kexec_purgatory.

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Daniel Micay <danielmicay@...il.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2: use extern instead of __weak void *; ebiederm
> ---
>  kernel/kexec_file.c     | 7 -------
>  kernel/kexec_internal.h | 2 ++
>  2 files changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index b118735fea9d..7a147a7add2e 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -26,13 +26,6 @@
>  #include <linux/vmalloc.h>
>  #include "kexec_internal.h"
>  
> -/*
> - * Declare these symbols weak so that if architecture provides a purgatory,
> - * these will be overridden.
> - */
> -char __weak kexec_purgatory[0];
> -size_t __weak kexec_purgatory_size = 0;
> -
>  static int kexec_calculate_store_digests(struct kimage *image);
>  
>  /* Architectures can provide this probe function */
> diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h
> index 799a8a452187..50dfcb039a41 100644
> --- a/kernel/kexec_internal.h
> +++ b/kernel/kexec_internal.h
> @@ -17,6 +17,8 @@ extern struct mutex kexec_mutex;
>  #ifdef CONFIG_KEXEC_FILE
>  #include <linux/purgatory.h>
>  void kimage_file_post_load_cleanup(struct kimage *image);
> +extern char kexec_purgatory[];
> +extern size_t kexec_purgatory_size;
>  #else /* CONFIG_KEXEC_FILE */
>  static inline void kimage_file_post_load_cleanup(struct kimage *image) { }
>  #endif /* CONFIG_KEXEC_FILE */
> -- 
> 2.7.4