linux-hardening - Re: [PATCH v2][next] acpi: nfit: intel: Avoid multiple -Wflex-array-member-not-at-end warnings

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Message-ID: <df338a70-fdfc-427e-9915-8b9e50de93ad@embeddedor.com>
Date: Wed, 30 Apr 2025 13:41:39 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Dan Williams <dan.j.williams@...el.com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Alison Schofield <alison.schofield@...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>
Cc: nvdimm@...ts.linux.dev, linux-acpi@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2][next] acpi: nfit: intel: Avoid multiple
 -Wflex-array-member-not-at-end warnings



On 27/03/25 08:03, Dan Williams wrote:
> 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 `DEFINE_RAW_FLEX()` helper for on-stack definitions of
>> a flexible structure where the size of the flexible-array member
>> is known at compile-time, and refactor the rest of the code,
>> accordingly.
>>
>> So, with these changes, fix a dozen of the following warnings:
>>
>> 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]
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> ---
>> Changes in v2:
>>   - Use DEFINE_RAW_FLEX() instead of __struct_group().
>>
>> v1:
>>   - Link: https://lore.kernel.org/linux-hardening/Z618ILbAR8YAvTkd@kspp/
>>
>>   drivers/acpi/nfit/intel.c | 388 ++++++++++++++++++--------------------
>>   1 file changed, 179 insertions(+), 209 deletions(-)
>>
>> diff --git a/drivers/acpi/nfit/intel.c b/drivers/acpi/nfit/intel.c
>> index 3902759abcba..114d5b3bb39b 100644
>> --- a/drivers/acpi/nfit/intel.c
>> +++ b/drivers/acpi/nfit/intel.c
>> @@ -55,21 +55,17 @@ 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 = {
>> -		.pkg = {
>> -			.nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
>> -			.nd_family = NVDIMM_FAMILY_INTEL,
>> -			.nd_size_out =
>> -				sizeof(struct nd_intel_get_security_state),
>> -			.nd_fw_size =
>> -				sizeof(struct nd_intel_get_security_state),
>> -		},
>> -	};
>> +	DEFINE_RAW_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
>> +			sizeof(struct nd_intel_get_security_state));
>> +	struct nd_intel_get_security_state *cmd =
>> +			(struct nd_intel_get_security_state *)nd_cmd->nd_payload;
>>   	int rc;
>>   
>> +	nd_cmd->nd_command = NVDIMM_INTEL_GET_SECURITY_STATE;
>> +	nd_cmd->nd_family = NVDIMM_FAMILY_INTEL;
>> +	nd_cmd->nd_size_out = sizeof(struct nd_intel_get_security_state);
>> +	nd_cmd->nd_fw_size = sizeof(struct nd_intel_get_security_state);
> 
> Can this keep the C99 init-style with something like (untested):
> 
> _DEFINE_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
>               sizeof(struct nd_intel_get_security_state), {
> 		.pkg = {
> 		        .nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
> 		        .nd_family = NVDIMM_FAMILY_INTEL,
> 		        .nd_size_out =
> 		                sizeof(struct nd_intel_get_security_state),
> 		        .nd_fw_size =
> 		                sizeof(struct nd_intel_get_security_state),
> 		},
> 	});
> 	
> 
> ?

The code below works - however, notice that in this case we should
go through 'obj', which is an object defined in _DEFINE_FLEX().

         _DEFINE_FLEX(struct nd_cmd_pkg, nd_cmd, nd_payload,
                         sizeof(struct nd_intel_get_security_state), = {
                 .obj = {
                         .nd_command = NVDIMM_INTEL_GET_SECURITY_STATE,
                         .nd_family = NVDIMM_FAMILY_INTEL,
                         .nd_size_out =
                                 sizeof(struct nd_intel_get_security_state),
                         .nd_fw_size =
                                 sizeof(struct nd_intel_get_security_state),
                 },
         });

Thanks
-Gustavo