linux-kernel - [PATCH] ARM: crypto: work around gcc-15 warning

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Message-Id: <20250610093256.2645686-1-arnd@kernel.org>
Date: Tue, 10 Jun 2025 11:32:52 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Russell King <linux@...linux.org.uk>,
	Ard Biesheuvel <ardb@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	Eric Biggers <ebiggers@...gle.com>,
	Jeff Johnson <jeff.johnson@....qualcomm.com>,
	linux-crypto@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] ARM: crypto: work around gcc-15 warning

From: Arnd Bergmann <arnd@...db.de>

I get a very rare -Wstringop-overread warning with gcc-15 for one function
in aesbs_ctr_encrypt():

arch/arm/crypto/aes-neonbs-glue.c: In function 'ctr_encrypt':
arch/arm/crypto/aes-neonbs-glue.c:212:1446: error: '__builtin_memcpy' offset [17, 2147483647] is out of the bounds [0, 16] of object 'buf' with type 'u8[16]' {aka 'unsigned char[16]'} [-Werror=array-bounds=]
  212 |                         src = dst = memcpy(buf + sizeof(buf) - bytes,
arch/arm/crypto/aes-neonbs-glue.c: In function 'ctr_encrypt':
arch/arm/crypto/aes-neonbs-glue.c:218:17: error: 'aesbs_ctr_encrypt' reading 1 byte from a region of size 0 [-Werror=stringop-overread]
  218 |                 aesbs_ctr_encrypt(dst, src, ctx->rk, ctx->rounds, bytes, walk.iv);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
arch/arm/crypto/aes-neonbs-glue.c:218:17: note: referencing argument 2 of type 'const u8[0]' {aka 'const unsigned char[]'}
arch/arm/crypto/aes-neonbs-glue.c:218:17: note: referencing argument 3 of type 'const u8[0]' {aka 'const unsigned char[]'}
arch/arm/crypto/aes-neonbs-glue.c:218:17: note: referencing argument 6 of type 'u8[0]' {aka 'unsigned char[]'}
arch/arm/crypto/aes-neonbs-glue.c:36:17: note: in a call to function 'aesbs_ctr_encrypt'
   36 | asmlinkage void aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],

This could happen in theory if walk.nbytes is larger than INT_MAX and gets
converted to a negative local variable.

Keep the type unsigned like the orignal nbytes to be sure there is no
integer overflow.

Fixes: c8bf850e991a ("crypto: arm/aes-neonbs-ctr - deal with non-multiples of AES block size")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arm/crypto/aes-neonbs-glue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/crypto/aes-neonbs-glue.c b/arch/arm/crypto/aes-neonbs-glue.c
index c60104dc1585..df5afe601e4a 100644
--- a/arch/arm/crypto/aes-neonbs-glue.c
+++ b/arch/arm/crypto/aes-neonbs-glue.c
@@ -206,7 +206,7 @@ static int ctr_encrypt(struct skcipher_request *req)
 	while (walk.nbytes > 0) {
 		const u8 *src = walk.src.virt.addr;
 		u8 *dst = walk.dst.virt.addr;
-		int bytes = walk.nbytes;
+		unsigned int bytes = walk.nbytes;
 
 		if (unlikely(bytes < AES_BLOCK_SIZE))
 			src = dst = memcpy(buf + sizeof(buf) - bytes,
-- 
2.39.5