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    Subject[PATCH 3.10 082/104] s390/bpf,jit: fix 32 bit divisions, use unsigned divide instructions
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

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

    From: Heiko Carstens <heiko.carstens@de.ibm.com>

    [ Upstream commit 3af57f78c38131b7a66e2b01e06fdacae01992a3 ]

    The s390 bpf jit compiler emits the signed divide instructions "dr" and "d"
    for unsigned divisions.
    This can cause problems: the dividend will be zero extended to a 64 bit value
    and the divisor is the 32 bit signed value as specified A or X accumulator,
    even though A and X are supposed to be treated as unsigned values.

    The divide instrunctions will generate an exception if the result cannot be
    expressed with a 32 bit signed value.
    This is the case if e.g. the dividend is 0xffffffff and the divisor either 1
    or also 0xffffffff (signed: -1).

    To avoid all these issues simply use unsigned divide instructions.

    Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/s390/net/bpf_jit_comp.c | 16 ++++++++--------
    1 file changed, 8 insertions(+), 8 deletions(-)

    --- a/arch/s390/net/bpf_jit_comp.c
    +++ b/arch/s390/net/bpf_jit_comp.c
    @@ -335,16 +335,16 @@ static int bpf_jit_insn(struct bpf_jit *
    EMIT4_PCREL(0xa7840000, (jit->ret0_ip - jit->prg));
    /* lhi %r4,0 */
    EMIT4(0xa7480000);
    - /* dr %r4,%r12 */
    - EMIT2(0x1d4c);
    + /* dlr %r4,%r12 */
    + EMIT4(0xb997004c);
    break;
    case BPF_S_ALU_DIV_K: /* A /= K */
    if (K == 1)
    break;
    /* lhi %r4,0 */
    EMIT4(0xa7480000);
    - /* d %r4,<d(K)>(%r13) */
    - EMIT4_DISP(0x5d40d000, EMIT_CONST(K));
    + /* dl %r4,<d(K)>(%r13) */
    + EMIT6_DISP(0xe340d000, 0x0097, EMIT_CONST(K));
    break;
    case BPF_S_ALU_MOD_X: /* A %= X */
    jit->seen |= SEEN_XREG | SEEN_RET0;
    @@ -354,8 +354,8 @@ static int bpf_jit_insn(struct bpf_jit *
    EMIT4_PCREL(0xa7840000, (jit->ret0_ip - jit->prg));
    /* lhi %r4,0 */
    EMIT4(0xa7480000);
    - /* dr %r4,%r12 */
    - EMIT2(0x1d4c);
    + /* dlr %r4,%r12 */
    + EMIT4(0xb997004c);
    /* lr %r5,%r4 */
    EMIT2(0x1854);
    break;
    @@ -367,8 +367,8 @@ static int bpf_jit_insn(struct bpf_jit *
    }
    /* lhi %r4,0 */
    EMIT4(0xa7480000);
    - /* d %r4,<d(K)>(%r13) */
    - EMIT4_DISP(0x5d40d000, EMIT_CONST(K));
    + /* dl %r4,<d(K)>(%r13) */
    + EMIT6_DISP(0xe340d000, 0x0097, EMIT_CONST(K));
    /* lr %r5,%r4 */
    EMIT2(0x1854);
    break;



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