Re: [PATCH] parisc: Fix csum_ipv6_magic on 32-bit systems

[Charlie Jenkins <charlie@rivosinc.com>]

On Sat, Feb 10, 2024 at 11:15:56AM -0800, Guenter Roeck wrote:
> 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
> 

Looks good!

Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>