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

[Andrii Nakryiko]

On Tue, Sep 10, 2024 at 12:17 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > >  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@xxxxxxxxxx>
> >
> > [...]
> >
> > > @@ -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?

I'd say let's do it, unlikely we'll break anyone. I'd expect everyone
doing explicit return 0 or return 1 anyways.

>
> thanks,
> jirka
>
> >
> > > +       return ret;
> > >  }
> > >
> >
> > [...]