linux-hardening - Re: [PATCH][next] crypto/nx: Avoid -Wflex-array-member-not-at-end warning

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Date: Thu, 28 Mar 2024 18:46:32 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Haren Myneni <haren@...ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	linuxppc-dev@...ts.ozlabs.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH][next] crypto/nx: Avoid -Wflex-array-member-not-at-end
 warning

On Tue, Mar 05, 2024 at 01:57:56PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end is coming in GCC-14, and we are getting
> ready to enable it globally. So, we are deprecating flexible-array
> members in the middle of another structure.
> 
> There is currently an object (`header`) in `struct nx842_crypto_ctx`
> that contains a flexible structure (`struct nx842_crypto_header`):
> 
> struct nx842_crypto_ctx {
> 	...
>         struct nx842_crypto_header header;
>         struct nx842_crypto_header_group group[NX842_CRYPTO_GROUP_MAX];
> 	...
> };
> 
> So, in order to avoid ending up with a flexible-array member in the
> middle of another struct, we use the `struct_group_tagged()` helper to
> separate the flexible array from the rest of the members in the flexible
> structure:
> 
> struct nx842_crypto_header {
> 	struct_group_tagged(nx842_crypto_header_hdr, hdr,
> 
> 		... the rest of the members
> 
> 	);
>         struct nx842_crypto_header_group group[];
> } __packed;
> 
> With the change described above, we can now declare an object of the
> type of the tagged struct, without embedding the flexible array in the
> middle of another struct:
> 
> struct nx842_crypto_ctx {
> 	...
>         struct nx842_crypto_header_hdr header;
>         struct nx842_crypto_header_group group[NX842_CRYPTO_GROUP_MAX];
> 	...
>  } __packed;
> 
> We also use `container_of()` whenever we need to retrieve a pointer to
> the flexible structure, through which we can access the flexible
> array if needed.
> 
> So, with these changes, fix the following warning:
> 
> In file included from drivers/crypto/nx/nx-842.c:55:
> drivers/crypto/nx/nx-842.h:174:36: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
>   174 |         struct nx842_crypto_header header;
>       |                                    ^~~~~~
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  drivers/crypto/nx/nx-842.c |  6 ++++--
>  drivers/crypto/nx/nx-842.h | 10 ++++++----
>  2 files changed, 10 insertions(+), 6 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt