From 6e61dc9da0b7a0d91d57c2e20b5ea4fd2d4e7e53 Mon Sep 17 00:00:00 2001 From: Ilya Leoshkevich Date: Tue, 7 Sep 2021 13:41:16 +0200 Subject: [PATCH] s390/bpf: Fix 64-bit subtraction of the -0x80000000 constant The JIT uses agfi for subtracting constants, but -(-0x80000000) cannot be represented as a 32-bit signed binary integer. Fix by using algfi in this particular case. Reported-by: Johan Almbladh Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend") Reviewed-by: Heiko Carstens Signed-off-by: Ilya Leoshkevich Signed-off-by: Vasily Gorbik --- arch/s390/net/bpf_jit_comp.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index c3bd630e9b43..245f98d5f690 100644 --- a/arch/s390/net/bpf_jit_comp.c +++ b/arch/s390/net/bpf_jit_comp.c @@ -794,8 +794,13 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, case BPF_ALU64 | BPF_SUB | BPF_K: /* dst = dst - imm */ if (!imm) break; - /* agfi %dst,-imm */ - EMIT6_IMM(0xc2080000, dst_reg, -imm); + if (imm == -0x80000000) { + /* algfi %dst,0x80000000 */ + EMIT6_IMM(0xc20a0000, dst_reg, 0x80000000); + } else { + /* agfi %dst,-imm */ + EMIT6_IMM(0xc2080000, dst_reg, -imm); + } break; /* * BPF_MUL