linux-kernel - Re: [PATCH bpf-next v3 2/2] bpf: Refactor bpf_tracing_func_proto() and remove bpf_get_probe_write

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Message-ID: <Z0i4DFnqRxTPOUfJ@elver.google.com>
Date: Thu, 28 Nov 2024 19:35:56 +0100
From: Marco Elver <elver@...gle.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Nikola Grcevski <nikola.grcevski@...fana.com>,
	bpf <bpf@...r.kernel.org>,
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 2/2] bpf: Refactor bpf_tracing_func_proto()
 and remove bpf_get_probe_write_proto()

On Thu, Nov 28, 2024 at 10:22AM -0800, Alexei Starovoitov wrote:
[..]
> Moving bpf_base_func_proto() all the way to the top was incorrect,
> but here we can move it just above this bpf_token_capable() check
> and remove extra indent like:
> 
> func_proto = bpf_base_func_proto();
> if (func_proto)
>    return func_proto;
> if (!bpf_token_capable(prog->aux->token, CAP_SYS_ADMIN))
>    return NULL;
> switch (func_id) {
> case BPF_FUNC_probe_write_user:
> 
> that will align it with the style of bpf_base_func_proto().
> 
> pw-bot: cr

Ack, let me change that.

Below is preview of v4 for this bit.

@@ -1417,6 +1409,8 @@ late_initcall(bpf_key_sig_kfuncs_init);
 static const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
+	const struct bpf_func_proto *func_proto;
+
 	switch (func_id) {
 	case BPF_FUNC_map_lookup_elem:
 		return &bpf_map_lookup_elem_proto;
@@ -1458,9 +1452,6 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_perf_event_read_proto;
 	case BPF_FUNC_get_prandom_u32:
 		return &bpf_get_prandom_u32_proto;
-	case BPF_FUNC_probe_write_user:
-		return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ?
-		       NULL : bpf_get_probe_write_proto();
 	case BPF_FUNC_probe_read_user:
 		return &bpf_probe_read_user_proto;
 	case BPF_FUNC_probe_read_kernel:
@@ -1539,7 +1530,22 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_trace_vprintk:
 		return bpf_get_trace_vprintk_proto();
 	default:
-		return bpf_base_func_proto(func_id, prog);
+		break;
+	}
+
+	func_proto = bpf_base_func_proto(func_id, prog);
+	if (func_proto)
+		return func_proto;
+
+	if (!bpf_token_capable(prog->aux->token, CAP_SYS_ADMIN))
+		return NULL;
+
+	switch (func_id) {
+	case BPF_FUNC_probe_write_user:
+		return security_locked_down(LOCKDOWN_BPF_WRITE_USER) < 0 ?
+		       NULL : &bpf_probe_write_user_proto;
+	default:
+		return NULL;
 	}
 }