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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>
This commit is contained in:
Heiko Carstens 2014-01-17 09:37:15 +01:00 committed by David S. Miller
parent 75b99dbd63
commit 3af57f78c3
1 changed files with 8 additions and 8 deletions
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16
arch/s390/net/bpf_jit_comp.c
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@ -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;