linux-kernel - Re: [PATCH] mm: unhide get_dump

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Message-ID: <202502241038.A4A1ED25A1@keescook>
Date: Mon, 24 Feb 2025 10:40:19 -0800
From: Kees Cook <kees@...nel.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Brian Mak <makb@...iper.net>,
	Arnd Bergmann <arnd@...db.de>, David Hildenbrand <david@...hat.com>,
	Peter Xu <peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
	John Hubbard <jhubbard@...dia.com>,
	Steve Sistare <steven.sistare@...cle.com>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Yang Shi <yang@...amperecomputing.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: unhide get_dump_page() function

On Mon, Feb 24, 2025 at 04:12:21PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The definition of get_dump_page() is guarded by CONFIG_ELF_CORE, but
> the caller has now moved into a function that is built based on
> CONFIG_COREDUMP, which leads to a possible link failure:
> 
> ld.lld-21: error: undefined symbol: get_dump_page
> >>> referenced by coredump.c
> >>>               fs/coredump.o:(dump_vma_snapshot) in archive vmlinux.a
> 
> Change the #ifdef block around the definition to match the caller.
> In practice there is very little difference, as setting COREDUMP
> but not ELF_CORE is not useful.
> 
> Fixes: ff41385709f0 ("coredump: Only sort VMAs when truncating or core_sort_vma sysctl is set")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for this! I think I'm going to split up ff41385709f0 -- between
this #ifdef and the recent prototype changes, it's going to be not a
great backport, so I'll pick this up too. I expect I'll have a simple
sysctl fix for -rc5 and then the rest in -next.

-Kees

> ---
>  mm/gup.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index d846c0ce41d6..15d6d7b5df1d 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2266,7 +2266,7 @@ EXPORT_SYMBOL(fault_in_readable);
>   *
>   * Called without mmap_lock (takes and releases the mmap_lock by itself).
>   */
> -#ifdef CONFIG_ELF_CORE
> +#ifdef CONFIG_COREDUMP
>  struct page *get_dump_page(unsigned long addr, int *locked)
>  {
>  	struct page *page;
> @@ -2276,7 +2276,7 @@ struct page *get_dump_page(unsigned long addr, int *locked)
>  				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
>  	return (ret == 1) ? page : NULL;
>  }
> -#endif /* CONFIG_ELF_CORE */
> +#endif /* CONFIG_COREDUMP */
>  
>  #ifdef CONFIG_MIGRATION
>  
> -- 
> 2.39.5
> 

-- 
Kees Cook