s390/bpf,jit: fix 32 bit divisions, use unsigned divide instructions

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>

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index fc0fa77728e15b6e69f1171504def520f9113542..708d60e4006676486b3892195b165ede007d2544 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -368,16 +368,16 @@ static int bpf_jit_insn(struct bpf_jit *jit, struct sock_filter *filter,
                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;
@@ -387,8 +387,8 @@ static int bpf_jit_insn(struct bpf_jit *jit, struct sock_filter *filter,
                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;
@@ -400,8 +400,8 @@ static int bpf_jit_insn(struct bpf_jit *jit, struct sock_filter *filter,
                }
                /* 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;