On Wed, Nov 8, 2023 at 6:01 AM Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx> wrote:
>
> The addition of is_reg_const() in commit 171de12646d2 ("bpf: generalize
> is_branch_taken to handle all conditional jumps in one place") has made the
> register_is_const() redundent. Give the former has more feature, plus the
typo: redundant
> fact the latter is only used in one place, replace register_is_const() with
> is_reg_const(), and remove the definition of register_is_const.
>
> This requires moving the definition of is_reg_const() further up. And since
> the comment of reg_const_value() reference is_reg_const(), move it up as
> well.
>
> Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@xxxxxxxx>
> ---
> kernel/bpf/verifier.c | 27 +++++++++++----------------
> 1 file changed, 11 insertions(+), 16 deletions(-)
>
I didn't notice duplication, but agree that it's best to unify. Thanks
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 2197385d91dc..a7651a861e42 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4685,9 +4685,17 @@ static bool register_is_null(struct bpf_reg_state *reg)
> return reg->type == SCALAR_VALUE && tnum_equals_const(reg->var_off, 0);
> }
>
> -static bool register_is_const(struct bpf_reg_state *reg)
> +/* check if register is a constant scalar value */
> +static bool is_reg_const(struct bpf_reg_state *reg, bool subreg32)
> {
> - return reg->type == SCALAR_VALUE && tnum_is_const(reg->var_off);
> + return reg->type == SCALAR_VALUE &&
> + tnum_is_const(subreg32 ? tnum_subreg(reg->var_off) : reg->var_off);
> +}
> +
> +/* assuming is_reg_const() is true, return constant value of a register */
> +static u64 reg_const_value(struct bpf_reg_state *reg, bool subreg32)
> +{
> + return subreg32 ? tnum_subreg(reg->var_off).value : reg->var_off.value;
> }
>
> static bool __is_scalar_unbounded(struct bpf_reg_state *reg)
> @@ -10030,7 +10038,7 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
> val = reg->var_off.value;
> max = map->max_entries;
>
> - if (!(register_is_const(reg) && val < max)) {
> + if (!(is_reg_const(reg, false) && val < max)) {
> bpf_map_key_store(aux, BPF_MAP_KEY_POISON);
> return 0;
> }
> @@ -14167,19 +14175,6 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
> }));
> }
>
> -/* check if register is a constant scalar value */
> -static bool is_reg_const(struct bpf_reg_state *reg, bool subreg32)
> -{
> - return reg->type == SCALAR_VALUE &&
> - tnum_is_const(subreg32 ? tnum_subreg(reg->var_off) : reg->var_off);
> -}
> -
> -/* assuming is_reg_const() is true, return constant value of a register */
> -static u64 reg_const_value(struct bpf_reg_state *reg, bool subreg32)
> -{
> - return subreg32 ? tnum_subreg(reg->var_off).value : reg->var_off.value;
> -}
> -
> /*
> * <reg1> <op> <reg2>, currently assuming reg2 is a constant
> */
>
> base-commit: 856624f12b04a3f51094fa277a31a333ee81cb3f
> --
> 2.42.0
>
