Re: [PATCH 4/4] bpf powerpc: Add addr > TASK_SIZE_MAX explicit check

[Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>]

> > @@ -763,6 +771,14 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
> >           /* dst = *(u16 *)(ul) (src + off) */
> >           case BPF_LDX | BPF_MEM | BPF_H:
> >           case BPF_LDX | BPF_PROBE_MEM | BPF_H:
> > +            if (BPF_MODE(code) == BPF_PROBE_MEM) {
> > +                EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], src_reg, off));
> > +                PPC_LI64(b2p[TMP_REG_2], TASK_SIZE_MAX);
> > +                EMIT(PPC_RAW_CMPLD(b2p[TMP_REG_1], b2p[TMP_REG_2]));
> > +                PPC_BCC(COND_GT, (ctx->idx + 4) * 4);
> > +                EMIT(PPC_RAW_XOR(dst_reg, dst_reg, dst_reg));
> > +                PPC_JMP((ctx->idx + 2) * 4);
> > +            }
>
> That code seems strictly identical to the previous one and the next one.
> Can you refactor in a function ?

I'll check this.

> >               EMIT(PPC_RAW_LHZ(dst_reg, src_reg, off));
> >               if (insn_is_zext(&insn[i + 1]))
> >                   addrs[++i] = ctx->idx * 4;
> > @@ -773,6 +789,14 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
> >           /* dst = *(u32 *)(ul) (src + off) */
> >           case BPF_LDX | BPF_MEM | BPF_W:
> >           case BPF_LDX | BPF_PROBE_MEM | BPF_W:
> > +            if (BPF_MODE(code) == BPF_PROBE_MEM) {
> > +                EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], src_reg, off));
> > +                PPC_LI64(b2p[TMP_REG_2], TASK_SIZE_MAX);
> > +                EMIT(PPC_RAW_CMPLD(b2p[TMP_REG_1], b2p[TMP_REG_2]));
> > +                PPC_BCC(COND_GT, (ctx->idx + 4) * 4);
> > +                EMIT(PPC_RAW_XOR(dst_reg, dst_reg, dst_reg));
> > +                PPC_JMP((ctx->idx + 2) * 4);
> > +            }
> >               EMIT(PPC_RAW_LWZ(dst_reg, src_reg, off));
> >               if (insn_is_zext(&insn[i + 1]))
> >                   addrs[++i] = ctx->idx * 4;
> > @@ -783,6 +807,20 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, struct codegen_context *
> >           /* dst = *(u64 *)(ul) (src + off) */
> >           case BPF_LDX | BPF_MEM | BPF_DW:
> >           case BPF_LDX | BPF_PROBE_MEM | BPF_DW:
> > +            if (BPF_MODE(code) == BPF_PROBE_MEM) {
> > +                EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], src_reg, off));
> > +                PPC_LI64(b2p[TMP_REG_2], TASK_SIZE_MAX);
> > +                EMIT(PPC_RAW_CMPLD(b2p[TMP_REG_1], b2p[TMP_REG_2]));
> > +                if (off % 4)
>
> That test is worth a comment.

(off % 4) test is based on how PPC_BPF_LL() emits instruction.

> And I'd prefer
>
>      if (off & 3) {
>          PPC_BCC(COND_GT, (ctx->idx + 5) * 4);
>          EMIT(PPC_RAW_XOR(dst_reg, dst_reg, dst_reg));
>          PPC_JMP((ctx->idx + 3) * 4);
>      } else {
>          PPC_BCC(COND_GT, (ctx->idx + 4) * 4);
>          EMIT(PPC_RAW_XOR(dst_reg, dst_reg, dst_reg));
>          PPC_JMP((ctx->idx + 2) * 4);
>      }

Yes this is neat.

Thanks for the review,
Ravi