linux-hardening - Re: [PATCH v2] md/bcache: Mark _

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Message-Id: <389A9925-0990-422C-A1B3-0195FAA73288@coly.li>
Date: Sat, 19 Apr 2025 11:55:10 +0800
From: Coly Li <i@...y.li>
To: Kees Cook <kees@...nel.org>
Cc: Coly Li <colyli@...nel.org>,
 Kent Overstreet <kent.overstreet@...ux.dev>,
 Ard Biesheuvel <ardb@...nel.org>,
 linux-bcache@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] md/bcache: Mark __nonstring look-up table



> 2025年4月19日 04:21，Kees Cook <kees@...nel.org> 写道：
> 
> GCC 15's new -Wunterminated-string-initialization notices that the 16
> character lookup table "zero_uuid" (which is not used as a C-String)
> needs to be marked as "nonstring":
> 
> drivers/md/bcache/super.c: In function 'uuid_find_empty':
> drivers/md/bcache/super.c:549:43: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (17 chars into 16 available) [-Wunterminated-string-initialization]
>  549 |         static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
>      |                                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Add the annotation (since it is not used as a C-String), and switch the
> initializer to an array of bytes.
> 
> Signed-off-by: Kees Cook <kees@...nel.org>
> ---
> v2: use byte array initializer (colyli)
> v1: https://lore.kernel.org/all/20250416220135.work.394-kees@kernel.org/
> Cc: Coly Li <colyli@...nel.org>
> Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: linux-bcache@...r.kernel.org
> ---
> drivers/md/bcache/super.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index e42f1400cea9..a76ce92502ed 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -546,7 +546,8 @@ static struct uuid_entry *uuid_find(struct cache_set *c, const char *uuid)
> 
> static struct uuid_entry *uuid_find_empty(struct cache_set *c)
> {
> - static const char zero_uuid[16] = "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0";
> + static const char zero_uuid[] __nonstring =

I notice zero_uuid[16] changes to zero_uuid[], then the element number information is removed.

Is it OK for GCC 15 to only add __nonstring and keep zero_uuid[16]?

Thanks.

Coly Li 


> + { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
> 
> return uuid_find(c, zero_uuid);
> }
> -- 
> 2.34.1
> 
>