Re: [PATCH RFCv3 08/23] uprobes/x86: Add uprobe syscall to speed up uprobe

[Jiri Olsa]

On Fri, Apr 04, 2025 at 01:33:07PM -0700, Andrii Nakryiko wrote:
> On Thu, Mar 20, 2025 at 4:43 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > Adding new uprobe syscall that calls uprobe handlers for given
> > 'breakpoint' address.
> >
> > The idea is that the 'breakpoint' address calls the user space
> > trampoline which executes the uprobe syscall.
> >
> > The syscall handler reads the return address of the initial call
> > to retrieve the original 'breakpoint' address. With this address
> > we find the related uprobe object and call its consumers.
> >
> > Adding the arch_uprobe_trampoline_mapping function that provides
> > uprobe trampoline mapping. This mapping is backed with one global
> > page initialized at __init time and shared by the all the mapping
> > instances.
> >
> > We do not allow to execute uprobe syscall if the caller is not
> > from uprobe trampoline mapping.
> >
> > The uprobe syscall ensures the consumer (bpf program) sees registers
> > values in the state before the trampoline was called.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> >  arch/x86/entry/syscalls/syscall_64.tbl |   1 +
> >  arch/x86/kernel/uprobes.c              | 134 +++++++++++++++++++++++++
> >  include/linux/syscalls.h               |   2 +
> >  include/linux/uprobes.h                |   1 +
> >  kernel/events/uprobes.c                |  22 ++++
> >  kernel/sys_ni.c                        |   1 +
> >  6 files changed, 161 insertions(+)
> >
> 
> [...]
> 
> > +void handle_syscall_uprobe(struct pt_regs *regs, unsigned long bp_vaddr)
> > +{
> > +       struct uprobe *uprobe;
> > +       int is_swbp;
> > +
> > +       rcu_read_lock_trace();
> > +       uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
> > +       if (!uprobe)
> > +               goto unlock;
> > +
> > +       if (!get_utask())
> > +               goto unlock;
> > +
> > +       if (arch_uprobe_ignore(&uprobe->arch, regs))
> > +               goto unlock;
> > +
> > +       handler_chain(uprobe, regs);
> > +
> > + unlock:
> > +       rcu_read_unlock_trace();
> 
> we now have `guard(rcu_tasks_trace)();`, let's use that in this
> function, seems like a good fit?

yes, will use it

thanks,
jirka

> 
> 
> > +}
> > +
> >  /*
> >   * Perform required fix-ups and disable singlestep.
> >   * Allow pending signals to take effect.
> > diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> > index c00a86931f8c..bf5d05c635ff 100644
> > --- a/kernel/sys_ni.c
> > +++ b/kernel/sys_ni.c
> > @@ -392,3 +392,4 @@ COND_SYSCALL(setuid16);
> >  COND_SYSCALL(rseq);
> >
> >  COND_SYSCALL(uretprobe);
> > +COND_SYSCALL(uprobe);
> > --
> > 2.49.0
> >