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Wed, 02 Apr 2025 12:19:48 -0700 (PDT) Received: from krava ([173.38.220.50]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39c0b7a422dsm18016034f8f.93.2025.04.02.12.19.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Apr 2025 12:19:48 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 2 Apr 2025 21:19:45 +0200 To: Jiri Olsa Cc: Andrii Nakryiko , Tao Chen , song@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, laoar.shao@gmail.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf-next 2/2] bpf: Check link_create parameter for multi_uprobe Message-ID: References: <20250331094745.336010-1-chen.dylane@linux.dev> <20250331094745.336010-2-chen.dylane@linux.dev> <918395a6-122c-4fb0-9761-892b8020b95e@linux.dev> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Apr 02, 2025 at 11:01:48AM +0200, Jiri Olsa wrote: > On Tue, Apr 01, 2025 at 03:06:22PM -0700, Andrii Nakryiko wrote: > > On Tue, Apr 1, 2025 at 5:40 AM Tao Chen wrote: > > > > > > 在 2025/4/1 19:03, Jiri Olsa 写道: > > > > On Mon, Mar 31, 2025 at 05:47:45PM +0800, Tao Chen wrote: > > > >> The target_fd and flags in link_create no used in multi_uprobe > > > >> , return -EINVAL if they assigned, keep it same as other link > > > >> attach apis. > > > >> > > > >> Fixes: 89ae89f53d20 ("bpf: Add multi uprobe link") > > > >> Signed-off-by: Tao Chen > > > >> --- > > > >> kernel/trace/bpf_trace.c | 3 +++ > > > >> 1 file changed, 3 insertions(+) > > > >> > > > >> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > > >> index 2f206a2a2..f7ebf17e3 100644 > > > >> --- a/kernel/trace/bpf_trace.c > > > >> +++ b/kernel/trace/bpf_trace.c > > > >> @@ -3385,6 +3385,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr > > > >> if (sizeof(u64) != sizeof(void *)) > > > >> return -EOPNOTSUPP; > > > >> > > > >> + if (attr->link_create.target_fd || attr->link_create.flags) > > > >> + return -EINVAL; > > > > > > > > I think the CI is failing because usdt code does uprobe multi detection > > > > with target_fd = -1 and it fails and perf-uprobe fallback will fail on > > > > not having enough file descriptors > > > > > > > > > > Hi jiri > > > > > > As you said, i found it, thanks. > > > > > > static int probe_uprobe_multi_link(int token_fd) > > > { > > > LIBBPF_OPTS(bpf_prog_load_opts, load_opts, > > > .expected_attach_type = BPF_TRACE_UPROBE_MULTI, > > > .token_fd = token_fd, > > > .prog_flags = token_fd ? BPF_F_TOKEN_FD : 0, > > > ); > > > LIBBPF_OPTS(bpf_link_create_opts, link_opts); > > > struct bpf_insn insns[] = { > > > BPF_MOV64_IMM(BPF_REG_0, 0), > > > BPF_EXIT_INSN(), > > > }; > > > int prog_fd, link_fd, err; > > > unsigned long offset = 0; > > > > > > prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL", > > > insns, ARRAY_SIZE(insns), &load_opts); > > > if (prog_fd < 0) > > > return -errno; > > > > > > /* Creating uprobe in '/' binary should fail with -EBADF. */ > > > link_opts.uprobe_multi.path = "/"; > > > link_opts.uprobe_multi.offsets = &offset; > > > link_opts.uprobe_multi.cnt = 1; > > > > > > link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, > > > &link_opts); > > > > > > > but I think at this stage we will brake some user apps by introducing > > > > this check, link ebpf go library, which passes 0 > > > > > > > > > > So is it ok just check the flags? > > > > good catch, Jiri! Yep, let's validate just flags? > > I think so.. I'll test that with ebpf/go to make sure we are safe > at least there ;-) I'll let you know sorry, got stuck.. link_create.flags are initialized to zero, so I think flags check should be fine (at least for ebpf/go) jirka