linux-kernel - Re: [PATCH bpf] bpf: use attach_btf instead of vmlinux in bpf_sk_storage_tracing

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Message-ID: <9e5b183e-5dd5-4d3d-b3e6-09ad5e7262dc@linux.dev>
Date: Thu, 16 Jan 2025 12:03:53 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jared Kangas <jkangas@...hat.com>
Cc: bpf@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, horms@...nel.org, martin.lau@...nel.org,
 ast@...nel.org, johannes.berg@...el.com, kafai@...com,
 songliubraving@...com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: use attach_btf instead of vmlinux in
 bpf_sk_storage_tracing_allowed

On 1/16/25 8:23 AM, Jared Kangas wrote:
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index 2f4ed83a75ae..74584dd12550 100644
> --- a/net/core/bpf_sk_storage.c
> +++ b/net/core/bpf_sk_storage.c
> @@ -352,8 +352,8 @@ const struct bpf_func_proto bpf_sk_storage_delete_proto = {
>   
>   static bool bpf_sk_storage_tracing_allowed(const struct bpf_prog *prog)
>   {
> -	const struct btf *btf_vmlinux;
>   	const struct btf_type *t;
> +	const struct btf *btf;
>   	const char *tname;
>   	u32 btf_id;
>   
> @@ -371,12 +371,12 @@ static bool bpf_sk_storage_tracing_allowed(const struct bpf_prog *prog)
>   		return true;
>   	case BPF_TRACE_FENTRY:
>   	case BPF_TRACE_FEXIT:
> -		btf_vmlinux = bpf_get_btf_vmlinux();
> -		if (IS_ERR_OR_NULL(btf_vmlinux))
> +		btf = prog->aux->attach_btf;
> +		if (!btf)
>   			return false;
>   		btf_id = prog->aux->attach_btf_id;
> -		t = btf_type_by_id(btf_vmlinux, btf_id);
> -		tname = btf_name_by_offset(btf_vmlinux, t->name_off);
> +		t = btf_type_by_id(btf, btf_id);
> +		tname = btf_name_by_offset(btf, t->name_off);
>   		return !!strncmp(tname, "bpf_sk_storage",
>   				 strlen("bpf_sk_storage"));

Thanks for the report.

There is a prog->aux->attach_func_name, so it can be directly used, like:

	case BPF_TRACE_FENTRY:
	case BPF_TRACE_FEXIT:
		return !!strncmp(prog->aux->attach_func_name, "bpf_sk_storage",
				 strlen("bpf_sk_storage"));

The above should do for the fix.

No need to check for null on attach_func_name. It should have been checked 
earlier in bpf_check_attach_target (the "tname" variable).

pw-bot: cr