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

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Message-Id: <20250312200700.make.521-kees@kernel.org>
Date: Wed, 12 Mar 2025 13:07:01 -0700
From: Kees Cook <kees@...nel.org>
To: Nicolas Ferre <nicolas.ferre@...rochip.com>
Cc: Kees Cook <kees@...nel.org>,
	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: [PATCH v3] net: macb: Add __nonstring annotations for unterminated strings

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@...nel.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@...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 | 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