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

[Jiri Olsa]

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?

thanks,
jirka

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