[PATCH 3.12 109/133] s390/bpf,jit: fix 32 bit divisions, use unsigned divide instructions

Greg Kroah-Hartman
2014-02-04T22:03:27Z

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
@@ -368,16 +368,16 @@ 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;
@@ -387,8 +387,8 @@ 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;
@@ -400,8 +400,8 @@ 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;