[PATCH v2 04/10] powerpc/bpf: Fix BPF_SUB when imm == 0x80000000

[Christophe Leroy]

Le 05/10/2021 à 22:25, Naveen N. Rao a écrit :
> 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>
> ---
> Changelog:
> - Split up BPF_ADD and BPF_SUB cases per Christophe's comments
> 
>   arch/powerpc/net/bpf_jit_comp64.c | 27 +++++++++++++++++----------
>   1 file changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index d67f6d62e2e1ff..6626e6c17d4ed2 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -330,18 +330,25 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
>   			EMIT(PPC_RAW_SUB(dst_reg, dst_reg, src_reg));
>   			goto bpf_alu32_trunc;
>   		case BPF_ALU | BPF_ADD | BPF_K: /* (u32) dst += (u32) imm */
> -		case BPF_ALU | BPF_SUB | BPF_K: /* (u32) dst -= (u32) imm */
>   		case BPF_ALU64 | BPF_ADD | BPF_K: /* dst += imm */
> +			if (!imm) {
> +				goto bpf_alu32_trunc;
> +			} else if (imm >= -32768 && imm < 32768) {
> +				EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, IMM_L(imm)));
> +			} else {
> +				PPC_LI32(b2p[TMP_REG_1], imm);
> +				EMIT(PPC_RAW_ADD(dst_reg, dst_reg, b2p[TMP_REG_1]));
> +			}
> +			goto bpf_alu32_trunc;
> +		case BPF_ALU | BPF_SUB | BPF_K: /* (u32) dst -= (u32) 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);
> -					EMIT(PPC_RAW_ADD(dst_reg, dst_reg, b2p[TMP_REG_1]));
> -				}
> +			if (!imm) {
> +				goto bpf_alu32_trunc;
> +			} else if (imm > -32768 && imm < 32768) {

Why do you exclude imm == 32768 ?


Reviewed-by: Christophe Leroy <christophe.leroy at csgroup.eu>



> +				EMIT(PPC_RAW_ADDI(dst_reg, dst_reg, IMM_L(-imm)));
> +			} else {
> +				PPC_LI32(b2p[TMP_REG_1], imm);
> +				EMIT(PPC_RAW_SUB(dst_reg, dst_reg, b2p[TMP_REG_1]));
>   			}
>   			goto bpf_alu32_trunc;
>   		case BPF_ALU | BPF_MUL | BPF_X: /* (u32) dst *= (u32) src */
>