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: <CAEf4BzYfh_oqMOCq8G1S48Ym3th4+wQS1=ZTgRE3OTQrAJnCMQ@mail.gmail.com>
Date: Mon, 22 Sep 2025 13:47:47 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>
Cc: 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 3:28 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> 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.

Ping. Any objections for landing this patch in bpf-next?

>
> >         if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
> >                 goto out;
> >
> > --
> > 2.51.0
> >