linux-kernel - Re: [PATCHv4 bpf-next 2/6] uprobe: Do not emulate/sstep original instruction when ip is changed

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Message-ID: <20250924084956.GW3245006@noisy.programming.kicks-ass.net>
Date: Wed, 24 Sep 2025 10:49:56 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	x86@...nel.org, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCHv4 bpf-next 2/6] uprobe: Do not emulate/sstep original
 instruction when ip is changed

On Tue, Sep 16, 2025 at 03:28:52PM -0700, Andrii Nakryiko wrote:
> On Tue, Sep 16, 2025 at 2:53 PM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > If uprobe handler changes instruction pointer we still execute single
> > step) or emulate the original instruction and increment the (new) ip
> > with its length.
> >
> > This makes the new instruction pointer bogus and application will
> > likely crash on illegal instruction execution.
> >
> > If user decided to take execution elsewhere, it makes little sense
> > to execute the original instruction, so let's skip it.
> >
> > Acked-by: Oleg Nesterov <oleg@...hat.com>
> > Acked-by: Andrii Nakryiko <andrii@...nel.org>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  kernel/events/uprobes.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index 7ca1940607bd..2b32c32bcb77 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -2741,6 +2741,13 @@ static void handle_swbp(struct pt_regs *regs)
> >
> >         handler_chain(uprobe, regs);
> >
> > +       /*
> > +        * If user decided to take execution elsewhere, it makes little sense
> > +        * to execute the original instruction, so let's skip it.
> > +        */
> > +       if (instruction_pointer(regs) != bp_vaddr)
> > +               goto out;
> > +
> 
> Peter, Ingo,
> 
> Are you guys ok with us routing this through the bpf-next tree? We'll
> have a tiny conflict because in perf/core branch there is
> arch_uprobe_optimize() call added after handler_chain(), so git merge
> will be a bit confused, probably. But it should be trivially
> resolvable.

Nah, I suppose that'll be fine. Thanks!