linux-kernel - Re: [PATCH v2] net: macb: Add __nonstring annotations for unterminated strings

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Message-ID: <20250318114933.GP688833@kernel.org>
Date: Tue, 18 Mar 2025 11:49:33 +0000
From: Simon Horman <horms@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] net: macb: Add __nonstring annotations for
 unterminated strings

On Tue, Mar 11, 2025 at 03:44:16PM -0700, Kees Cook wrote:
> When a character array without a terminating NUL character has a static
> initializer, GCC 15's -Wunterminated-string-initialization will only
> warn if the array lacks the "nonstring" attribute[1]. Mark the arrays
> with __nonstring to and correctly identify the char array as "not a C
> string" and thereby eliminate the warning.
> 
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
> Signed-off-by: Kees Cook <kees@...nel.org>
> ---
>  v1: https://lore.kernel.org/lkml/20250310222415.work.815-kees@kernel.org/
>  v2: switch to __nonstring annotation
> Cc: Nicolas Ferre <nicolas.ferre@...rochip.com>
> Cc: Claudiu Beznea <claudiu.beznea@...on.dev>
> Cc: Andrew Lunn <andrew+netdev@...n.ch>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> ---
>  drivers/net/ethernet/cadence/macb.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
> index 2847278d9cd4..003483073223 100644
> --- a/drivers/net/ethernet/cadence/macb.h
> +++ b/drivers/net/ethernet/cadence/macb.h
> @@ -1027,7 +1027,7 @@ struct gem_stats {
>   * this register should contribute to.
>   */
>  struct gem_statistic {
> -	char stat_string[ETH_GSTRING_LEN];
> +	char stat_string[ETH_GSTRING_LEN] __nonstring;

Hi Kees, all,

I see where this is going, and I have no objections to it.
But a member called *_string which is annotated as __nonstring
does seem a somewhat unintuitive.

>  	int offset;
>  	u32 stat_bits;
>  };
> @@ -1068,6 +1068,7 @@ static const struct gem_statistic gem_statistics[] = {
>  	GEM_STAT_TITLE(TX512CNT, "tx_512_1023_byte_frames"),
>  	GEM_STAT_TITLE(TX1024CNT, "tx_1024_1518_byte_frames"),
>  	GEM_STAT_TITLE(TX1519CNT, "tx_greater_than_1518_byte_frames"),
> +
>  	GEM_STAT_TITLE_BITS(TXURUNCNT, "tx_underrun",
>  			    GEM_BIT(NDS_TXERR)|GEM_BIT(NDS_TXFIFOERR)),
>  	GEM_STAT_TITLE_BITS(SNGLCOLLCNT, "tx_single_collision_frames",
> -- 
> 2.34.1
> 
>