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Sender: Guenter Roeck <groeck7@gmail.com>
From: Guenter Roeck <linux@roeck-us.net>
To: Helge Deller <deller@gmx.de>
Cc: "James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>,
	linux-parisc@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Guenter Roeck <linux@roeck-us.net>,
	Charlie Jenkins <charlie@rivosinc.com>,
	Palmer Dabbelt <palmer@rivosinc.com>
Subject: [PATCH] parisc: Fix csum_ipv6_magic on 32-bit systems
Date: Sat, 10 Feb 2024 11:15:56 -0800
Message-Id: <20240210191556.3761064-1-linux@roeck-us.net>
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Calculating the IPv6 checksum on 32-bit systems missed overflows when
adding the proto+len fields into the checksum. This results in the
following unit test failure.

    # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:506
    Expected ( u64)csum_result == ( u64)expected, but
        ( u64)csum_result == 46722 (0xb682)
        ( u64)expected == 46721 (0xb681)
    not ok 5 test_csum_ipv6_magic

This is probably rarely seen in the real world because proto+len are
usually small values which will rarely result in overflows when calculating
the checksum. However, the unit test code uses large values for the length
field, causing the test to fail.

Fix the problem by adding the missing carry into the final checksum.

Cc: Charlie Jenkins <charlie@rivosinc.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 arch/parisc/include/asm/checksum.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/parisc/include/asm/checksum.h b/arch/parisc/include/asm/checksum.h
index f705e5dd1074..e619e67440db 100644
--- a/arch/parisc/include/asm/checksum.h
+++ b/arch/parisc/include/asm/checksum.h
@@ -163,7 +163,8 @@ static __inline__ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 "	ldw,ma		4(%2), %7\n"	/* 4th daddr */
 "	addc		%6, %0, %0\n"
 "	addc		%7, %0, %0\n"
-"	addc		%3, %0, %0\n"	/* fold in proto+len, catch carry */
+"	addc		%3, %0, %0\n"	/* fold in proto+len */
+"	addc		0, %0, %0\n"	/* add carry */
 
 #endif
 	: "=r" (sum), "=r" (saddr), "=r" (daddr), "=r" (len),
-- 
2.39.2