Re: [PATCHv4 bpf-next 5/6] bpf: Return value in kprobe get_func_ip only for entry address

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Sep 23, 2022 at 02:42:07PM -0700, Andrii Nakryiko wrote:
> On Thu, Sep 22, 2022 at 2:04 PM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Changing return value of kprobe's version of bpf_get_func_ip
> > to return zero if the attach address is not on the function's
> > entry point.
> >
> > For kprobes attached in the middle of the function we can't easily
> > get to the function address especially now with the CONFIG_X86_KERNEL_IBT
> > support.
> >
> > If user cares about current IP for kprobes attached within the
> > function body, they can get it with PT_REGS_IP(ctx).
> >
> > Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  kernel/trace/bpf_trace.c                             | 5 ++++-
> >  tools/testing/selftests/bpf/progs/get_func_ip_test.c | 4 ++--
> >  2 files changed, 6 insertions(+), 3 deletions(-)
> >
> 
> Can you please add a note in bpf_get_func_ip() description in
> uapi/linux/bpf.h that this function returns zero for kprobes in the
> middle of the function?

yep, will do that

thanks,
jirka

> 
> With that:
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> 
> 
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index ebd1b348beb3..688552df95ca 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1048,7 +1048,10 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> >  {
> >         struct kprobe *kp = kprobe_running();
> >
> > -       return kp ? (uintptr_t)kp->addr : 0;
> > +       if (!kp || !(kp->flags & KPROBE_FLAG_ON_FUNC_ENTRY))
> > +               return 0;
> > +
> > +       return get_entry_ip((uintptr_t)kp->addr);
> >  }
> 
> [...]