From: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
[ Upstream commit 7477d43be5b1448bc0d4c85cb185a0144cc080e1 ]
Both signed and unsigned variants of BPF_JMP | BPF_K require
sign-extending the immediate. JIT emits cgfi for the signed case,
which is correct, and clgfi for the unsigned case, which is not
correct: clgfi zero-extends the immediate.
s390 does not provide an instruction that does sign-extension and
unsigned comparison at the same time. Therefore, fix by first loading
the sign-extended immediate into work register REG_1 and proceeding
as if it's BPF_X.
Fixes: 4e9b4a6883dd ("s390/bpf: Use relative long branches")
Reported-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Tested-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20200717165326.6786-3-iii@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/s390/net/bpf_jit_comp.c | 19 ++++---------------
1 file changed, 4 insertions(+), 15 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index f4242b894cf28..6b3d612948fba 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1417,21 +1417,10 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
}
break;
branch_ku:
- is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
- /* clfi or clgfi %dst,imm */
- EMIT6_IMM(is_jmp32 ? 0xc20f0000 : 0xc20e0000,
- dst_reg, imm);
- if (!is_first_pass(jit) &&
- can_use_rel(jit, addrs[i + off + 1])) {
- /* brc mask,off */
- EMIT4_PCREL_RIC(0xa7040000,
- mask >> 12, addrs[i + off + 1]);
- } else {
- /* brcl mask,off */
- EMIT6_PCREL_RILC(0xc0040000,
- mask >> 12, addrs[i + off + 1]);
- }
- break;
+ /* lgfi %w1,imm (load sign extend imm) */
+ src_reg = REG_1;
+ EMIT6_IMM(0xc0010000, src_reg, imm);
+ goto branch_xu;
branch_xs:
is_jmp32 = BPF_CLASS(insn->code) == BPF_JMP32;
if (!is_first_pass(jit) &&
--
2.25.1
