[PATCH 6/9] powerpc/bpf: Fix BPF_SUB when imm == 0x80000000

[Johan Almbladh]

On Fri, Oct 1, 2021 at 11:15 PM Naveen N. Rao
<naveen.n.rao at linux.vnet.ibm.com> wrote:
>
> We aren't handling subtraction involving an immediate value of
> 0x80000000 properly. Fix the same.
>
> Fixes: 156d0e290e969c ("powerpc/ebpf/jit: Implement JIT compiler for extended BPF")
> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>

Acked-by: Johan Almbladh <johan.almbladh at anyfinetworks.com>
Tested-by: Johan Almbladh <johan.almbladh at anyfinetworks.com>

> ---
>  arch/powerpc/net/bpf_jit_comp64.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index ffb7a2877a8469..4641a50e82d50d 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -333,15 +333,15 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>                 case BPF_ALU | BPF_SUB | BPF_K: /* (u32) dst -= (u32) imm */
>                 case BPF_ALU64 | BPF_ADD | BPF_K: /* dst += imm */
>                 case BPF_ALU64 | BPF_SUB | BPF_K: /* dst -= imm */
> -                       if (BPF_OP(code) == BPF_SUB)
> -                               imm = -imm;
> -                       if (imm) {
> -                               if (imm >= -32768 && imm < 32768)
> -                                       EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, IMM_L(imm)));
> -                               else {
> -                                       PPC_LI32(b2p[TMP_REG_1], imm);
> +                       if (imm > -32768 && imm < 32768) {
> +                               EMIT(PPC_RAW_ADDI(dst_reg, dst_reg,
> +                                       BPF_OP(code) == BPF_SUB ? IMM_L(-imm) : IMM_L(imm)));
> +                       } else {
> +                               PPC_LI32(b2p[TMP_REG_1], imm);
> +                               if (BPF_OP(code) == BPF_SUB)
> +                                       EMIT(PPC_RAW_SUB(dst_reg, dst_reg, b2p[TMP_REG_1]));
> +                               else
>                                         EMIT(PPC_RAW_ADD(dst_reg, dst_reg, b2p[TMP_REG_1]));
> -                               }
>                         }
>                         goto bpf_alu32_trunc;
>                 case BPF_ALU | BPF_MUL | BPF_X: /* (u32) dst *= (u32) src */
> --
> 2.33.0
>