Re: [PATCH bpf] s390/bpf: fix lcgr instruction encoding

[Vasily Gorbik <gor@linux.ibm.com>]

On Mon, Aug 12, 2019 at 05:03:32PM +0200, Ilya Leoshkevich wrote:
> "masking, test in bounds 3" fails on s390, because
> BPF_ALU64_IMM(BPF_NEG, BPF_REG_2, 0) ignores the top 32 bits of
> BPF_REG_2. The reason is that JIT emits lcgfr instead of lcgr.
> The associated comment indicates that the code was intended to emit lcgr
> in the first place, it's just that the wrong opcode was used.
> 
> Fix by using the correct opcode.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  arch/s390/net/bpf_jit_comp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
> index e636728ab452..6299156f9738 100644
> --- a/arch/s390/net/bpf_jit_comp.c
> +++ b/arch/s390/net/bpf_jit_comp.c
> @@ -863,7 +863,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp, int i
>  		break;
>  	case BPF_ALU64 | BPF_NEG: /* dst = -dst */
>  		/* lcgr %dst,%dst */
> -		EMIT4(0xb9130000, dst_reg, dst_reg);
> +		EMIT4(0xb9030000, dst_reg, dst_reg);
>  		break;
>  	/*
>  	 * BPF_FROM_BE/LE
> -- 
> 2.21.0
> 
Please add
Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
or whatever it should be. With that:
Acked-by: Vasily Gorbik <gor@linux.ibm.com>