netdev - [PATCH bpf 2/2] bpf: Require ARG_PTR_TO

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Message-Id: <20260107-helper_proto-v1-2-21fa523fccfd@gmail.com>
Date: Wed, 07 Jan 2026 20:16:48 +0800
From: Zesen Liu <ftyghome@...il.com>
To: 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>, Matt Bobrowski <mattbobrowski@...gle.com>, 
 Steven Rostedt <rostedt@...dmis.org>, 
 Masami Hiramatsu <mhiramat@...nel.org>, 
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Simon Horman <horms@...nel.org>, Daniel Xu <dxu@...uu.xyz>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-trace-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Shuran Liu <electronlsr@...il.com>, Peili Gao <gplhust955@...il.com>, 
 Haoran Ni <haoran.ni.cs@...il.com>, Zesen Liu <ftyghome@...il.com>
Subject: [PATCH bpf 2/2] bpf: Require ARG_PTR_TO_MEM with memory flag

Add check to ensure that ARG_PTR_TO_MEM is used with either MEM_WRITE or
MEM_RDONLY.

Using ARG_PTR_TO_MEM alone without tags does not make sense because:

- If the helper does not change the argument, missing MEM_RDONLY causes the
verifier to incorrectly reject a read-only buffer.
- If the helper does change the argument, missing MEM_WRITE causes the
verifier to incorrectly assume the memory is unchanged, leading to errors
in code optimization.

Co-developed-by: Shuran Liu <electronlsr@...il.com>
Signed-off-by: Shuran Liu <electronlsr@...il.com>
Co-developed-by: Peili Gao <gplhust955@...il.com>
Signed-off-by: Peili Gao <gplhust955@...il.com>
Co-developed-by: Haoran Ni <haoran.ni.cs@...il.com>
Signed-off-by: Haoran Ni <haoran.ni.cs@...il.com>
Signed-off-by: Zesen Liu <ftyghome@...il.com>
---
 kernel/bpf/verifier.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f0ca69f888fa..c7ebddb66385 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10349,10 +10349,27 @@ static bool check_btf_id_ok(const struct bpf_func_proto *fn)
 	return true;
 }

+static bool check_mem_arg_rw_flag_ok(const struct bpf_func_proto *fn)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(fn->arg_type); i++) {
+		enum bpf_arg_type arg_type = fn->arg_type[i];
+
+		if (base_type(arg_type) != ARG_PTR_TO_MEM)
+			continue;
+		if (!(arg_type & (MEM_WRITE | MEM_RDONLY)))
+			return false;
+	}
+
+	return true;
+}
+
 static int check_func_proto(const struct bpf_func_proto *fn, int func_id)
 {
 	return check_raw_mode_ok(fn) &&
 	       check_arg_pair_ok(fn) &&
+		   check_mem_arg_rw_flag_ok(fn) &&
 	       check_btf_id_ok(fn) ? 0 : -EINVAL;
 }

-- 
2.43.0