linux-hardening - [PATCH][next] crypto: nx - Use static

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Message-ID: <ZrVCAqGrl+5prW1Y@cute>
Date: Thu, 8 Aug 2024 16:09:06 -0600
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: Haren Myneni <haren@...ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>
Cc: linuxppc-dev@...ts.ozlabs.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: [PATCH][next] crypto: nx - Use static_assert() to check struct sizes

Commit 1e6b251ce175 ("crypto: nx - Avoid -Wflex-array-member-not-at-end
warning") introduced tagged `struct nx842_crypto_header_hdr`. We want
to ensure that when new members need to be added to the flexible
structure, they are always included within this tagged struct.

So, we use `static_assert()` to ensure that the memory layout for
both the flexible structure and the tagged struct is the same after
any changes.

Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/crypto/nx/nx-842.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/crypto/nx/nx-842.h b/drivers/crypto/nx/nx-842.h
index 25fa70b2112c..887d4ce3cb49 100644
--- a/drivers/crypto/nx/nx-842.h
+++ b/drivers/crypto/nx/nx-842.h
@@ -157,6 +157,7 @@ struct nx842_crypto_header_group {
 } __packed;
 
 struct nx842_crypto_header {
+	/* New members MUST be added within the struct_group() macro below. */
 	struct_group_tagged(nx842_crypto_header_hdr, hdr,
 		__be16 magic;		/* NX842_CRYPTO_MAGIC */
 		__be16 ignore;		/* decompressed end bytes to ignore */
@@ -164,6 +165,8 @@ struct nx842_crypto_header {
 	);
 	struct nx842_crypto_header_group group[];
 } __packed;
+static_assert(offsetof(struct nx842_crypto_header, group) == sizeof(struct nx842_crypto_header_hdr),
+	      "struct member likely outside of struct_group_tagged()");
 
 #define NX842_CRYPTO_GROUP_MAX	(0x20)
 
-- 
2.34.1