Re: [PATCH bpf-next v1 3/8] bpf: Introduce load-acquire and store-release instructions

[Eduard Zingerman]

On Sat, 2025-01-25 at 02:18 +0000, Peilin Ye wrote:

[...]

> +static int check_atomic_store(struct bpf_verifier_env *env, int insn_idx,
> +			      struct bpf_insn *insn)
> +{
> +	int err;
> +
> +	err = check_reg_arg(env, insn->src_reg, SRC_OP);
> +	if (err)
> +		return err;
> +
> +	err = check_reg_arg(env, insn->dst_reg, SRC_OP);
> +	if (err)
> +		return err;
> +
> +	if (is_pointer_value(env, insn->src_reg)) {
> +		verbose(env, "R%d leaks addr into mem\n", insn->src_reg);
> +		return -EACCES;
> +	}

Nit: this check is done by check_mem_access(), albeit only for
     PTR_TO_MEM, I think it's better to be consistent with
     what happens for regular stores and avoid this check here.

> +
> +	if (!atomic_ptr_type_ok(env, insn->dst_reg, insn)) {
> +		verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
> +			insn->dst_reg,
> +			reg_type_str(env, reg_state(env, insn->dst_reg)->type));
> +		return -EACCES;
> +	}
> +
> +	if (is_arena_reg(env, insn->dst_reg)) {
> +		err = save_aux_ptr_type(env, PTR_TO_ARENA, false);
> +		if (err)
> +			return err;
> +	}
> +
> +	/* Check whether we can write into the memory. */
> +	err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> +			       BPF_SIZE(insn->code), BPF_WRITE, insn->src_reg,
> +			       true, false);
> +	if (err)
> +		return err;
> +	return 0;
> +}

[...]