linux-kernel - Re: [PATCH v4][for-next/hardening] acpi: nfit: intel: avoid multiple -Wflex-array-member-not-at-end warnings

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Message-ID: <202506270850.8631FABC17@keescook>
Date: Fri, 27 Jun 2025 08:52:42 -0700
From: Kees Cook <kees@...nel.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>, Ira Weiny <ira.weiny@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, nvdimm@...ts.linux.dev,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4][for-next/hardening] acpi: nfit: intel: avoid multiple
 -Wflex-array-member-not-at-end warnings

On Wed, Jun 25, 2025 at 03:42:16PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the new TRAILING_OVERLAP() helper to fix a dozen instances of
> the following type of warning:
> 
> drivers/acpi/nfit/intel.c:692:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Acked-by: Dan Williams <dan.j.williams@...el.com>
> Tested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> This patch should go through:
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/ (for-next/hardening)
> 
> Changes in v4:
>  - Use the new TRAILING_OVERLAP() helper.
> 
> Changes in v3:
>  - Use union instead of DEFINE_RAW_FLEX().
>  - Link: https://lore.kernel.org/linux-hardening/aEneid7gdAZr1_kR@kspp/
> 
> Changes in v2:
>  - Use DEFINE_RAW_FLEX() instead of __struct_group().
>  - Link: https://lore.kernel.org/linux-hardening/Z-QpUcxFCRByYcTA@kspp/ 
> 
> v1:
>  - Link: https://lore.kernel.org/linux-hardening/Z618ILbAR8YAvTkd@kspp/
> 
>  drivers/acpi/nfit/intel.c | 84 +++++++++++++++++----------------------
>  1 file changed, 36 insertions(+), 48 deletions(-)
> 
> diff --git a/drivers/acpi/nfit/intel.c b/drivers/acpi/nfit/intel.c
> index 3902759abcba..d0b72e906428 100644
> --- a/drivers/acpi/nfit/intel.c
> +++ b/drivers/acpi/nfit/intel.c
> @@ -55,10 +55,9 @@ static unsigned long intel_security_flags(struct nvdimm *nvdimm,
>  {
>  	struct nfit_mem *nfit_mem = nvdimm_provider_data(nvdimm);
>  	unsigned long security_flags = 0;
> -	struct {
> -		struct nd_cmd_pkg pkg;
> -		struct nd_intel_get_security_state cmd;
> -	} nd_cmd = {
> +	TRAILING_OVERLAP(struct nd_cmd_pkg, pkg, nd_payload,
> +			 struct nd_intel_get_security_state cmd;
> +	) nd_cmd = {

If you wanted, these could be even further minimized to this, leaving
the trailing object indentation unchanged:

-	struct {
-		struct nd_cmd_pkg pkg;
+	TRAILING_OVERLAP(struct nd_cmd_pkg, pkg, nd_payload,
 		struct nd_intel_get_security_state cmd;
-	} nd_cmd = {
+	) nd_cmd = {

-- 
Kees Cook