linux-kernel - [PATCH] ACPI: tables: Add __nonstring annotations for unterminated strings

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Message-Id: <20250415232028.work.843-kees@kernel.org>
Date: Tue, 15 Apr 2025 16:20:29 -0700
From: Kees Cook <kees@...nel.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Kees Cook <kees@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Robert Moore <robert.moore@...el.com>,
	linux-acpi@...r.kernel.org,
	acpica-devel@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] ACPI: tables: 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 4-byte
ACPI identifier arrays with __nonstring (and the new __nonstring_array)
to correctly identify the char arrays as "not C strings" and thereby
eliminate the many warnings like this:

In file included from include/acpi/actbl.h:371,
                 from include/acpi/acpi.h:26,
                 from include/linux/acpi.h:26,
                 from drivers/acpi/tables.c:19:
include/acpi/actbl1.h:30:33: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (5 chars into 4 available) [-Wunterminated-string-initialization]
   30 | #define ACPI_SIG_BERT           "BERT"  /* Boot Error Record Table */
      |                                 ^~~~~~
drivers/acpi/tables.c:400:9: note: in expansion of macro 'ACPI_SIG_BERT'
  400 |         ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
      |         ^~~~~~~~~~~~~

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
Signed-off-by: Kees Cook <kees@...nel.org>
---
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Len Brown <lenb@...nel.org>
Cc: Robert Moore <robert.moore@...el.com>
Cc: linux-acpi@...r.kernel.org
Cc: acpica-devel@...ts.linux.dev
---
 drivers/acpi/tables.c | 2 +-
 include/acpi/actbl.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/tables.c b/drivers/acpi/tables.c
index 2295abbecd14..0a9ade7117bd 100644
--- a/drivers/acpi/tables.c
+++ b/drivers/acpi/tables.c
@@ -396,7 +396,7 @@ static u8 __init acpi_table_checksum(u8 *buffer, u32 length)
 }
 
 /* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
-static const char table_sigs[][ACPI_NAMESEG_SIZE] __initconst = {
+static const char table_sigs[][ACPI_NAMESEG_SIZE] __nonstring_array __initconst = {
 	ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
 	ACPI_SIG_EINJ, ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT,
 	ACPI_SIG_MSCT, ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT,
diff --git a/include/acpi/actbl.h b/include/acpi/actbl.h
index 451f6276da49..2fc89704be17 100644
--- a/include/acpi/actbl.h
+++ b/include/acpi/actbl.h
@@ -66,7 +66,7 @@
  ******************************************************************************/
 
 struct acpi_table_header {
-	char signature[ACPI_NAMESEG_SIZE];	/* ASCII table signature */
+	char signature[ACPI_NAMESEG_SIZE] __nonstring;	/* ASCII table signature */
 	u32 length;		/* Length of table in bytes, including this header */
 	u8 revision;		/* ACPI Specification minor version number */
 	u8 checksum;		/* To make sum of entire table == 0 */
-- 
2.34.1