linux-kernel - Re: [PATCH 02/13] kprobe: Keep traced function address

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Date:   Thu, 6 Jan 2022 09:31:40 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        lkml <linux-kernel@...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>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 02/13] kprobe: Keep traced function address

On Wed, Jan 05, 2022 at 08:30:48PM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 4, 2022 at 12:10 AM Jiri Olsa <jolsa@...hat.com> wrote:
> >
> > The bpf_get_func_ip_kprobe helper should return traced function
> > address, but it's doing so only for kprobes that are placed on
> > the function entry.
> >
> > If kprobe is placed within the function, bpf_get_func_ip_kprobe
> > returns that address instead of function entry.
> >
> > Storing the function entry directly in kprobe object, so it could
> > be used in bpf_get_func_ip_kprobe helper.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  include/linux/kprobes.h                              |  3 +++
> >  kernel/kprobes.c                                     | 12 ++++++++++++
> >  kernel/trace/bpf_trace.c                             |  2 +-
> >  tools/testing/selftests/bpf/progs/get_func_ip_test.c |  4 ++--
> >  4 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> > index 8c8f7a4d93af..a204df4fef96 100644
> > --- a/include/linux/kprobes.h
> > +++ b/include/linux/kprobes.h
> > @@ -74,6 +74,9 @@ struct kprobe {
> >         /* Offset into the symbol */
> >         unsigned int offset;
> >
> > +       /* traced function address */
> > +       unsigned long func_addr;
> > +
> 
> keep in mind that we'll also need (maybe in a follow up series) to
> store bpf_cookie somewhere close to this func_addr as well. Just
> mentioning to keep in mind as you decide with Masami where to put it.

ok

SNIP

> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 21aa30644219..25631253084a 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1026,7 +1026,7 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> >  {
> >         struct kprobe *kp = kprobe_running();
> >
> > -       return kp ? (uintptr_t)kp->addr : 0;
> > +       return kp ? (uintptr_t)kp->func_addr : 0;
> >  }
> >
> >  static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
> > diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > index a587aeca5ae0..e988aefa567e 100644
> > --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > @@ -69,7 +69,7 @@ int test6(struct pt_regs *ctx)
> >  {
> >         __u64 addr = bpf_get_func_ip(ctx);
> >
> > -       test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
> > +       test6_result = (const void *) addr == &bpf_fentry_test6;
> >         return 0;
> >  }
> >
> > @@ -79,6 +79,6 @@ int test7(struct pt_regs *ctx)
> >  {
> >         __u64 addr = bpf_get_func_ip(ctx);
> >
> > -       test7_result = (const void *) addr == &bpf_fentry_test7 + 5;
> > +       test7_result = (const void *) addr == &bpf_fentry_test7;
> 
> we can treat this as a bug fix for bpf_get_func_ip() for kprobes,
> right? I think "Fixes: " tag is in order then.

true, will add that in next version

thanks,
jirka