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[PATCH v3] net: macb: Add __nonstring annotations for unterminated strings

Kees Cook posted 1 patch 9 months, 1 week ago 
drivers/net/ethernet/cadence/macb.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
[PATCH v3] net: macb: Add __nonstring annotations for unterminated strings
Posted by Kees Cook 9 months, 1 week ago 
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 correctly identify the char array as "not a C string"
and thereby eliminate the warning:

In file included from ../drivers/net/ethernet/cadence/macb_main.c:42:
../drivers/net/ethernet/cadence/macb.h:1070:35: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (33 chars into 32 available) [-Wunterminated-string-initialization]
 1070 |         GEM_STAT_TITLE(TX1519CNT, "tx_greater_than_1518_byte_frames"),
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/net/ethernet/cadence/macb.h:1050:24: note: in definition of macro 'GEM_STAT_TITLE_BITS'
 1050 |         .stat_string = title,                           \
      |                        ^~~~~
../drivers/net/ethernet/cadence/macb.h:1070:9: note: in expansion of macro 'GEM_STAT_TITLE'
 1070 |         GEM_STAT_TITLE(TX1519CNT, "tx_greater_than_1518_byte_frames"),
      |         ^~~~~~~~~~~~~~
../drivers/net/ethernet/cadence/macb.h:1097:35: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (33 chars into 32 available) [-Wunterminated-string-initialization]
 1097 |         GEM_STAT_TITLE(RX1519CNT, "rx_greater_than_1518_byte_frames"),
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/net/ethernet/cadence/macb.h:1050:24: note: in definition of macro 'GEM_STAT_TITLE_BITS'
 1050 |         .stat_string = title,                           \
      |                        ^~~~~
../drivers/net/ethernet/cadence/macb.h:1097:9: note: in expansion of macro 'GEM_STAT_TITLE'
 1097 |         GEM_STAT_TITLE(RX1519CNT, "rx_greater_than_1518_byte_frames"),
      |         ^~~~~~~~~~~~~~

Since these strings are copied with memcpy() they do not need to be
NUL terminated, and can use __nonstring:

                        memcpy(p, gem_statistics[i].stat_string,
                               ETH_GSTRING_LEN);

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
 v3: improve commit message (Bill), drop whitespace change (Bill)
 v2: https://lore.kernel.org/lkml/20250311224412.it.153-kees@kernel.org/
 v1: https://lore.kernel.org/lkml/20250310222415.work.815-kees@kernel.org/
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: netdev@vger.kernel.org
---
 drivers/net/ethernet/cadence/macb.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
index 2847278d9cd4..d2a4c180d6a6 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;
 	int offset;
 	u32 stat_bits;
 };
-- 
2.34.1
Re: [PATCH v3] net: macb: Add __nonstring annotations for unterminated strings
Posted by Andrew Lunn 9 months, 1 week ago 
>  struct gem_statistic {
> -	char stat_string[ETH_GSTRING_LEN];
> +	char stat_string[ETH_GSTRING_LEN] __nonstring;

This general pattern of a char foo[ETH_GSTRING_LEN]' will appear
throughout drivers/net/ethernet. Maybe Coccinelle can find them all
and add the __nonstring ?

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew
Re: [PATCH v3] net: macb: Add __nonstring annotations for unterminated strings
Posted by Kees Cook 9 months, 1 week ago 
On Thu, Mar 13, 2025 at 02:25:09PM +0100, Andrew Lunn wrote:
> >  struct gem_statistic {
> > -	char stat_string[ETH_GSTRING_LEN];
> > +	char stat_string[ETH_GSTRING_LEN] __nonstring;
> 
> This general pattern of a char foo[ETH_GSTRING_LEN]' will appear
> throughout drivers/net/ethernet. Maybe Coccinelle can find them all
> and add the __nonstring ?

I had that same thought but then rediscovered ethtool_puts() and
ethtool_sprintf(), which operate on C Strings and write out C Strings...
so _some_ ethtool stats are being constructed in a way that we can't
just universally apply __nonstring to all ETH_GSTRING_LEN strings. :(

-- 
Kees Cook
Re: [PATCH v3] net: macb: Add __nonstring annotations for unterminated strings
Posted by Jacob Keller 9 months, 1 week ago 

On 3/12/2025 1:07 PM, 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 correctly identify the char array as "not a C string"
> and thereby eliminate the warning:
> 
> In file included from ../drivers/net/ethernet/cadence/macb_main.c:42:
> ../drivers/net/ethernet/cadence/macb.h:1070:35: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (33 chars into 32 available) [-Wunterminated-string-initialization]
>  1070 |         GEM_STAT_TITLE(TX1519CNT, "tx_greater_than_1518_byte_frames"),
>       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/net/ethernet/cadence/macb.h:1050:24: note: in definition of macro 'GEM_STAT_TITLE_BITS'
>  1050 |         .stat_string = title,                           \
>       |                        ^~~~~
> ../drivers/net/ethernet/cadence/macb.h:1070:9: note: in expansion of macro 'GEM_STAT_TITLE'
>  1070 |         GEM_STAT_TITLE(TX1519CNT, "tx_greater_than_1518_byte_frames"),
>       |         ^~~~~~~~~~~~~~
> ../drivers/net/ethernet/cadence/macb.h:1097:35: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (33 chars into 32 available) [-Wunterminated-string-initialization]
>  1097 |         GEM_STAT_TITLE(RX1519CNT, "rx_greater_than_1518_byte_frames"),
>       |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/net/ethernet/cadence/macb.h:1050:24: note: in definition of macro 'GEM_STAT_TITLE_BITS'
>  1050 |         .stat_string = title,                           \
>       |                        ^~~~~
> ../drivers/net/ethernet/cadence/macb.h:1097:9: note: in expansion of macro 'GEM_STAT_TITLE'
>  1097 |         GEM_STAT_TITLE(RX1519CNT, "rx_greater_than_1518_byte_frames"),
>       |         ^~~~~~~~~~~~~~
> 
> Since these strings are copied with memcpy() they do not need to be
> NUL terminated, and can use __nonstring:
> 
>                         memcpy(p, gem_statistics[i].stat_string,
>                                ETH_GSTRING_LEN);
> 
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

>  v3: improve commit message (Bill), drop whitespace change (Bill)
>  v2: https://lore.kernel.org/lkml/20250311224412.it.153-kees@kernel.org/
>  v1: https://lore.kernel.org/lkml/20250310222415.work.815-kees@kernel.org/
> Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
> Cc: Claudiu Beznea <claudiu.beznea@tuxon.dev>
> Cc: Andrew Lunn <andrew+netdev@lunn.ch>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: netdev@vger.kernel.org
> ---
>  drivers/net/ethernet/cadence/macb.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb.h b/drivers/net/ethernet/cadence/macb.h
> index 2847278d9cd4..d2a4c180d6a6 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;
>  	int offset;
>  	u32 stat_bits;
>  };

Patchew 2.1-devel-b67e4c2

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