| From | Kamal Mostafa <> | Subject | [PATCH 3.8 118/124] s390/bpf,jit: fix 32 bit divisions, use unsigned divide instructions | Date | Mon, 10 Feb 2014 11:40:58 -0800 |
| |
3.8.13.18 -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: Kamal Mostafa <kamal@canonical.com> --- arch/s390/net/bpf_jit_comp.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index fd01c59..5e92f47 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -332,16 +332,16 @@ 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; @@ -351,8 +351,8 @@ 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; @@ -364,8 +364,8 @@ 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; -- 1.8.3.2
|