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    Subject[PATCH 4.9 22/27] powerpc/64: Fix checksum folding in csum_tcpudp_nofold and ip_fast_csum_nofold
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Paul Mackerras <paulus@ozlabs.org>

    commit b492f7e4e07a28e706db26cf4943bb0911435426 upstream.

    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 <paulus@ozlabs.org>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/powerpc/include/asm/checksum.h | 17 ++++++++++++-----
    1 file changed, 12 insertions(+), 5 deletions(-)

    --- a/arch/powerpc/include/asm/checksum.h
    +++ b/arch/powerpc/include/asm/checksum.h
    @@ -53,17 +53,25 @@ static inline __sum16 csum_fold(__wsum s
    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, __u32 len,
    __u8 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\
    @@ -123,8 +131,7 @@ static inline __wsum ip_fast_csum_nofold

    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;


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