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Commit 3af57f78 authored by Heiko Carstens's avatar Heiko Carstens Committed by David S. Miller
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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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 75b99dbd

arch/s390/net/bpf_jit_comp.c

+8 −8
Original line number Diff line number Diff line
@@ -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;