linux-kernel - Re: [PATCHv3 2/7] bpf: Add support for uprobe multi session attach

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Message-ID: <Zt_ygFPEdX53rqaW@krava>
Date: Tue, 10 Sep 2024 09:17:20 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...omium.org>,
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCHv3 2/7] bpf: Add support for uprobe multi session attach

On Mon, Sep 09, 2024 at 04:44:29PM -0700, Andrii Nakryiko wrote:
> On Mon, Sep 9, 2024 at 12:46 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Adding support to attach bpf program for entry and return probe
> > of the same function. This is common use case which at the moment
> > requires to create two uprobe multi links.
> >
> > Adding new BPF_TRACE_UPROBE_SESSION attach type that instructs
> > kernel to attach single link program to both entry and exit probe.
> >
> > It's possible to control execution of the bpf program on return
> > probe simply by returning zero or non zero from the entry bpf
> > program execution to execute or not the bpf program on return
> > probe respectively.
> >
> 
> pedantic nit: bpf -> BPF

ok

> 
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  include/uapi/linux/bpf.h       |  1 +
> >  kernel/bpf/syscall.c           |  9 +++++++--
> >  kernel/trace/bpf_trace.c       | 32 ++++++++++++++++++++++++--------
> >  tools/include/uapi/linux/bpf.h |  1 +
> >  tools/lib/bpf/libbpf.c         |  1 +
> >  5 files changed, 34 insertions(+), 10 deletions(-)
> >
> 
> LGTM
> 
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> 
> [...]
> 
> > @@ -3336,9 +3347,13 @@ uprobe_multi_link_handler(struct uprobe_consumer *con, struct pt_regs *regs,
> >                           __u64 *data)
> >  {
> >         struct bpf_uprobe *uprobe;
> > +       int ret;
> >
> >         uprobe = container_of(con, struct bpf_uprobe, consumer);
> > -       return uprobe_prog_run(uprobe, instruction_pointer(regs), regs);
> > +       ret = uprobe_prog_run(uprobe, instruction_pointer(regs), regs);
> > +       if (uprobe->consumer.session)
> > +               return ret ? UPROBE_HANDLER_IGNORE : 0;
> 
> Should we restrict the return range to [0, 1] for UPROBE_SESSION
> programs on the verifier side (given it's a new program type and we
> can do that)?

yes, I think we can do that.. we have BPF_TRACE_UPROBE_SESSION as
expected_attach_type so we can do that during the load

hum, is it too late to do that for kprobe session as well?

thanks,
jirka

> 
> > +       return ret;
> >  }
> >
> 
> [...]