From: Ilya Leoshkevich iii@linux.ibm.com
[ 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@canonical.com Signed-off-by: Ilya Leoshkevich iii@linux.ibm.com Signed-off-by: Alexei Starovoitov ast@kernel.org Tested-by: Seth Forshee seth.forshee@canonical.com Link: https://lore.kernel.org/bpf/20200717165326.6786-3-iii@linux.ibm.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 0f37a1b635f85..ac227ea13cbe7 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -1416,21 +1416,10 @@ 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) &&