linux-kernel - Re: [RFC bpf-next 01/10] uprobe: Add session callbacks to uprobe

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Date: Wed, 5 Jun 2024 23:01:21 +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: [RFC bpf-next 01/10] uprobe: Add session callbacks to
 uprobe_consumer

On Wed, Jun 05, 2024 at 10:25:56AM -0700, Andrii Nakryiko wrote:

SNIP

> > ---
> >  include/linux/uprobes.h | 18 +++++++++++
> >  kernel/events/uprobes.c | 69 +++++++++++++++++++++++++++++++++++------
> >  2 files changed, 78 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> > index f46e0ca0169c..a2f2d5ac3cee 100644
> > --- a/include/linux/uprobes.h
> > +++ b/include/linux/uprobes.h
> > @@ -34,6 +34,12 @@ enum uprobe_filter_ctx {
> >  };
> >
> >  struct uprobe_consumer {
> > +       /*
> > +        * The handler callback return value controls removal of the uprobe.
> > +        *  0 on success, uprobe stays
> > +        *  1 on failure, remove the uprobe
> > +        *    console warning for anything else
> > +        */
> >         int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
> >         int (*ret_handler)(struct uprobe_consumer *self,
> >                                 unsigned long func,
> > @@ -42,6 +48,17 @@ struct uprobe_consumer {
> >                                 enum uprobe_filter_ctx ctx,
> >                                 struct mm_struct *mm);
> >
> > +       /* The handler_session callback return value controls execution of
> > +        * the return uprobe and ret_handler_session callback.
> > +        *  0 on success
> > +        *  1 on failure, DO NOT install/execute the return uprobe
> > +        *    console warning for anything else
> > +        */
> > +       int (*handler_session)(struct uprobe_consumer *self, struct pt_regs *regs,
> > +                              unsigned long *data);
> > +       int (*ret_handler_session)(struct uprobe_consumer *self, unsigned long func,
> > +                                  struct pt_regs *regs, unsigned long *data);
> > +
> 
> We should try to avoid an alternative set of callbacks, IMO. Let's
> extend existing ones with `unsigned long *data`, but specify that
> unless consumer sets some flag on registration that it needs a session
> cookie, we'll pass NULL here? Or just allocate cookie data for each
> registered consumer for simplicity, don't know; given we don't expect
> many consumers on exactly the same uprobe, it might be ok to keep it
> simple.
>

ah, I did not want to break existing users.. but it's not uapi,
so we're good, ok makes sense

jirka
 
> 
> >         struct uprobe_consumer *next;
> >  };
> >
> > @@ -85,6 +102,7 @@ struct return_instance {
> >         unsigned long           func;
> >         unsigned long           stack;          /* stack pointer */
> >         unsigned long           orig_ret_vaddr; /* original return address */
> > +       unsigned long           data;
> >         bool                    chained;        /* true, if instance is nested */
> >
> >         struct return_instance  *next;          /* keep as stack */

SNIP