[PATCH 1/2] powerpc/64: Fix checksum folding in csum_tcpudp_nofold and ip_fast_csum_nofold
From: Paul Mackerras <hidden>
Date: 2016-11-03 05:15:58
These functions compute an IP checksum by computing a 64-bit sum and folding it to 32 bits (the "nofold" in their names refers to folding down to 16 bits). However, doing (u32) (s + (s >> 32)) is not sufficient to fold a 64-bit sum to 32 bits correctly. The addition can produce a carry out from bit 31, which needs to be added in to the sum to produce the correct result. To fix this, we copy the from64to32() function from lib/checksum.c and use that. Signed-off-by: Paul Mackerras <redacted> --- arch/powerpc/include/asm/checksum.h | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/include/asm/checksum.h b/arch/powerpc/include/asm/checksum.h
index ee655ed..c16c6f8 100644
--- a/arch/powerpc/include/asm/checksum.h
+++ b/arch/powerpc/include/asm/checksum.h@@ -53,19 +53,27 @@ static inline __sum16 csum_fold(__wsum sum) return (__force __sum16)(~((__force u32)sum + tmp) >> 16); } +static inline u32 from64to32(u64 x) +{ + /* add up 32-bit and 32-bit for 32+c bit */ + x = (x & 0xffffffff) + (x >> 32); + /* add up carry.. */ + x = (x & 0xffffffff) + (x >> 32); + return (u32)x; +} + static inline __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr, unsigned short len, unsigned short proto, __wsum sum) { #ifdef __powerpc64__ - unsigned long s = (__force u32)sum; + u64 s = (__force u32)sum; s += (__force u32)saddr; s += (__force u32)daddr; s += proto + len; - s += (s >> 32); - return (__force __wsum) s; + return (__force __wsum) from64to32(s); #else __asm__("\n\ addc %0,%0,%1 \n\
@@ -127,8 +135,7 @@ static inline __wsum ip_fast_csum_nofold(const void *iph, unsigned int ihl) for (i = 0; i < ihl - 1; i++, ptr++) s += *ptr; - s += (s >> 32); - return (__force __wsum)s; + return (__force __wsum)from64to32(s); #else __wsum sum, tmp;
--
2.10.1