netdev - Re: [RFC PATCH v9 01/11] bpf: Support getting referenced kptr from struct

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Message-ID: <907f24f2-0f33-415e-85c6-0400ab67f896@linux.dev>
Date: Tue, 23 Jul 2024 17:32:49 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Amery Hung <ameryhung@...il.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, yangpeihao@...u.edu.cn,
 daniel@...earbox.net, andrii@...nel.org, alexei.starovoitov@...il.com,
 martin.lau@...nel.org, sinquersw@...il.com, toke@...hat.com,
 jhs@...atatu.com, jiri@...nulli.us, sdf@...gle.com,
 xiyou.wangcong@...il.com, yepeilin.cs@...il.com
Subject: Re: [RFC PATCH v9 01/11] bpf: Support getting referenced kptr from
 struct_ops argument

On 7/14/24 10:51 AM, Amery Hung wrote:
> @@ -21004,6 +21025,13 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
>   		mark_reg_known_zero(env, regs, BPF_REG_1);
>   	}
>   
> +	if (env->prog->type == BPF_PROG_TYPE_STRUCT_OPS) {
> +		ctx_arg_info = (struct bpf_ctx_arg_aux *)env->prog->aux->ctx_arg_info;
> +		for (i = 0; i < env->prog->aux->ctx_arg_info_size; i++)
> +			if (ctx_arg_info[i].refcounted)
> +				ctx_arg_info[i].ref_obj_id = acquire_reference_state(env, 0);
> +	}
> +

I think this will miss a case when passing the struct_ops prog ctx (i.e. "__u64 
*ctx") to a global subprog. Something like this:

__noinline int subprog_release(__u64 *ctx __arg_ctx)
{
	struct task_struct *task = (struct task_struct *)ctx[1];
	int dummy = (int)ctx[0];

	bpf_task_release(task);

	return dummy + 1;
}

SEC("struct_ops/subprog_ref")
__failure
int test_subprog_ref(__u64 *ctx)
{
	struct task_struct *task = (struct task_struct *)ctx[1];

	bpf_task_release(task);

	return subprog_release(ctx);;
}

SEC(".struct_ops.link")
struct bpf_testmod_ops subprog_ref = {
	.test_refcounted = (void *)test_subprog_ref,
};

A quick thought is, I think tracking the ctx's ref id in the env->cur_state may 
not be the correct place.

[ Just want to bring up what I have noticed so far. I will stop at here for 
today and will continue. ]