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([2620:10d:c090:500::3:93b1]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b6b367cbc9sm20058248eec.32.2026.01.20.10.06.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jan 2026 10:06:11 -0800 (PST) Message-ID: <34ff0901e3c96cbfab8b7325012e44d6d290a9be.camel@gmail.com> Subject: Re: [PATCH bpf-next v3 2/2] bpf: Require ARG_PTR_TO_MEM with memory flag From: Eduard Zingerman To: Zesen Liu , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Matt Bobrowski , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Daniel Xu Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, netdev@vger.kernel.org, Shuran Liu , Peili Gao , Haoran Ni Date: Tue, 20 Jan 2026 10:06:07 -0800 In-Reply-To: <20260120-helper_proto-v3-2-27b0180b4e77@gmail.com> References: <20260120-helper_proto-v3-0-27b0180b4e77@gmail.com> <20260120-helper_proto-v3-2-27b0180b4e77@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.2 (3.58.2-1.fc43) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2026-01-20 at 16:28 +0800, Zesen Liu wrote: > Add check to ensure that ARG_PTR_TO_MEM is used with either MEM_WRITE or > MEM_RDONLY. >=20 > Using ARG_PTR_TO_MEM alone without flags does not make sense because: >=20 > - If the helper does not change the argument, missing MEM_RDONLY causes t= he > 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. >=20 > Co-developed-by: Shuran Liu > Signed-off-by: Shuran Liu > Co-developed-by: Peili Gao > Signed-off-by: Peili Gao > Co-developed-by: Haoran Ni > Signed-off-by: Haoran Ni > Signed-off-by: Zesen Liu > --- At the moment, for helper arguments processing I see that MEM_RDONLY influences verifier only when argument type is ARG_PTR_TO_DYNPTR or ARG_PTR_TO_BTF_ID. Hence, I think this change is safe to apply, effects are limited to the check_mem_arg_rw_flag_ok() below. Reviewed-by: Eduard Zingerman > kernel/bpf/verifier.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) >=20 > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 9de0ec0c3ed9..a89f5bc7eff7 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -10351,10 +10351,27 @@ static bool check_btf_id_ok(const struct bpf_fu= nc_proto *fn) > return true; > } > =20 > +static bool check_mem_arg_rw_flag_ok(const struct bpf_func_proto *fn) > +{ > + int i; > + > + for (i =3D 0; i < ARRAY_SIZE(fn->arg_type); i++) { > + enum bpf_arg_type arg_type =3D fn->arg_type[i]; > + > + if (base_type(arg_type) !=3D 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) > { > 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; > } > =20