linux-kernel - Re: [PATCH v3 06/16] csky: kprobes: Use generic kretprobe trampoline handler

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Date:   Sat, 29 Aug 2020 18:31:39 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Guo Ren <guoren@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Eddy Wu <Eddy_Wu@...ndmicro.com>, x86@...nel.org,
        "David S . Miller" <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 06/16] csky: kprobes: Use generic kretprobe
 trampoline handler

On Fri, 28 Aug 2020 20:34:22 +0800
Guo Ren <guoren@...nel.org> wrote:

> Looks more clear.
> 
> Acked-by: Guo Ren <guoren@...nel.org>

Thanks Guo! I'll add it to the next version.

> 
> On Fri, Aug 28, 2020 at 12:39 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  arch/csky/kernel/probes/kprobes.c |   78 +------------------------------------
> >  1 file changed, 3 insertions(+), 75 deletions(-)
> >
> > diff --git a/arch/csky/kernel/probes/kprobes.c b/arch/csky/kernel/probes/kprobes.c
> > index f0f733b7ac5a..a891fb422e76 100644
> > --- a/arch/csky/kernel/probes/kprobes.c
> > +++ b/arch/csky/kernel/probes/kprobes.c
> > @@ -404,87 +404,15 @@ int __init arch_populate_kprobe_blacklist(void)
> >
> >  void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> >  {
> > -       struct kretprobe_instance *ri = NULL;
> > -       struct hlist_head *head, empty_rp;
> > -       struct hlist_node *tmp;
> > -       unsigned long flags, orig_ret_address = 0;
> > -       unsigned long trampoline_address =
> > -               (unsigned long)&kretprobe_trampoline;
> > -       kprobe_opcode_t *correct_ret_addr = NULL;
> > -
> > -       INIT_HLIST_HEAD(&empty_rp);
> > -       kretprobe_hash_lock(current, &head, &flags);
> > -
> > -       /*
> > -        * It is possible to have multiple instances associated with a given
> > -        * task either because multiple functions in the call path have
> > -        * return probes installed on them, and/or more than one
> > -        * return probe was registered for a target function.
> > -        *
> > -        * We can handle this because:
> > -        *     - instances are always pushed into the head of the list
> > -        *     - when multiple return probes are registered for the same
> > -        *       function, the (chronologically) first instance's ret_addr
> > -        *       will be the real return address, and all the rest will
> > -        *       point to kretprobe_trampoline.
> > -        */
> > -       hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> > -               if (ri->task != current)
> > -                       /* another task is sharing our hash bucket */
> > -                       continue;
> > -
> > -               orig_ret_address = (unsigned long)ri->ret_addr;
> > -
> > -               if (orig_ret_address != trampoline_address)
> > -                       /*
> > -                        * This is the real return address. Any other
> > -                        * instances associated with this task are for
> > -                        * other calls deeper on the call stack
> > -                        */
> > -                       break;
> > -       }
> > -
> > -       kretprobe_assert(ri, orig_ret_address, trampoline_address);
> > -
> > -       correct_ret_addr = ri->ret_addr;
> > -       hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> > -               if (ri->task != current)
> > -                       /* another task is sharing our hash bucket */
> > -                       continue;
> > -
> > -               orig_ret_address = (unsigned long)ri->ret_addr;
> > -               if (ri->rp && ri->rp->handler) {
> > -                       __this_cpu_write(current_kprobe, &ri->rp->kp);
> > -                       get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> > -                       ri->ret_addr = correct_ret_addr;
> > -                       ri->rp->handler(ri, regs);
> > -                       __this_cpu_write(current_kprobe, NULL);
> > -               }
> > -
> > -               recycle_rp_inst(ri, &empty_rp);
> > -
> > -               if (orig_ret_address != trampoline_address)
> > -                       /*
> > -                        * This is the real return address. Any other
> > -                        * instances associated with this task are for
> > -                        * other calls deeper on the call stack
> > -                        */
> > -                       break;
> > -       }
> > -
> > -       kretprobe_hash_unlock(current, &flags);
> > -
> > -       hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
> > -               hlist_del(&ri->hlist);
> > -               kfree(ri);
> > -       }
> > -       return (void *)orig_ret_address;
> > +       return (void *)kretprobe_trampoline_handler(regs,
> > +                       (unsigned long)&kretprobe_trampoline, NULL);
> >  }
> >
> >  void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> >                                       struct pt_regs *regs)
> >  {
> >         ri->ret_addr = (kprobe_opcode_t *)regs->lr;
> > +       ri->fp = NULL;
> >         regs->lr = (unsigned long) &kretprobe_trampoline;
> >  }
> >
> >
> 
> 
> -- 
> Best Regards
>  Guo Ren
> 
> ML: https://lore.kernel.org/linux-csky/


-- 
Masami Hiramatsu <mhiramat@...nel.org>