Subject: Re: [PATCH 3/4] kprobes: move kprobe_ftrace_handler() from x86 and make it weak

From: Jisheng Zhang <[email-masked]>
Date: Tue, 20 Aug 2019 01:56:23 +0000

On Tue, 20 Aug 2019 09:07:35 +0900 Masami Hiramatsu  wrote:

> Hi Jisheng,

Hi,

> 
> On Mon, 19 Aug 2019 11:37:32 +0000
> Jisheng Zhang <[email-masked]> wrote:
> 
> > This code could be reused. So move it from x86 to common code.  
> 
> Yes, it can be among some arch, but at first, please make your
> architecture implementation. After making sure that is enough
> stable, we will optimize (consolidate) the code.

Got it. I will duplicate the function firstly then make the consolidation
as a TODO.

> 
> For example,
> > -             /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
> > -             instruction_pointer_set(regs, ip + sizeof(kprobe_opcode_t));  
> 
> This may depend on arch implementation of kprobes.

Indeed, for arm64, would be as simple as s/ip/pc. 

Thanks

> 
> Could you make a copy and update comments on arm64?
> 
> Thank you,
> 
> >
> > Signed-off-by: Jisheng Zhang <[email-masked]>
> > ---
> >  arch/x86/kernel/kprobes/ftrace.c | 44 --------------------------------
> >  kernel/kprobes.c                 | 44 ++++++++++++++++++++++++++++++++
> >  2 files changed, 44 insertions(+), 44 deletions(-)
> >
> > diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
> > index c2ad0b9259ca..91ae1e3e65f7 100644
> > --- a/arch/x86/kernel/kprobes/ftrace.c
> > +++ b/arch/x86/kernel/kprobes/ftrace.c
> > @@ -12,50 +12,6 @@
> >
> >  #include "common.h"
> >
> > -/* Ftrace callback handler for kprobes -- called under preepmt disabed */
> > -void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> > -                        struct ftrace_ops *ops, struct pt_regs *regs)
> > -{
> > -     struct kprobe *p;
> > -     struct kprobe_ctlblk *kcb;
> > -
> > -     /* Preempt is disabled by ftrace */
> > -     p = get_kprobe((kprobe_opcode_t *)ip);
> > -     if (unlikely(!p) || kprobe_disabled(p))
> > -             return;
> > -
> > -     kcb = get_kprobe_ctlblk();
> > -     if (kprobe_running()) {
> > -             kprobes_inc_nmissed_count(p);
> > -     } else {
> > -             unsigned long orig_ip = instruction_pointer(regs);
> > -             /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
> > -             instruction_pointer_set(regs, ip + sizeof(kprobe_opcode_t));
> > -
> > -             __this_cpu_write(current_kprobe, p);
> > -             kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> > -             if (!p->pre_handler || !p->pre_handler(p, regs)) {
> > -                     /*
> > -                      * Emulate singlestep (and also recover regs->ip)
> > -                      * as if there is a 5byte nop
> > -                      */
> > -                     instruction_pointer_set(regs,
> > -                             (unsigned long)p->addr + MCOUNT_INSN_SIZE);
> > -                     if (unlikely(p->post_handler)) {
> > -                             kcb->kprobe_status = KPROBE_HIT_SSDONE;
> > -                             p->post_handler(p, regs, 0);
> > -                     }
> > -                     instruction_pointer_set(regs, orig_ip);
> > -             }
> > -             /*
> > -              * If pre_handler returns !0, it changes regs->ip. We have to
> > -              * skip emulating post_handler.
> > -              */
> > -             __this_cpu_write(current_kprobe, NULL);
> > -     }
> > -}
> > -NOKPROBE_SYMBOL(kprobe_ftrace_handler);
> > -
> >  int arch_prepare_kprobe_ftrace(struct kprobe *p)
> >  {
> >       p->ainsn.insn = NULL;
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index f8400753a8a9..479148ee1822 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -960,6 +960,50 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
> >  #endif /* CONFIG_OPTPROBES */
> >
> >  #ifdef CONFIG_KPROBES_ON_FTRACE
> > +/* Ftrace callback handler for kprobes -- called under preepmt disabed */
> > +void __weak kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> > +                               struct ftrace_ops *ops, struct pt_regs *regs)
> > +{
> > +     struct kprobe *p;
> > +     struct kprobe_ctlblk *kcb;
> > +
> > +     /* Preempt is disabled by ftrace */
> > +     p = get_kprobe((kprobe_opcode_t *)ip);
> > +     if (unlikely(!p) || kprobe_disabled(p))
> > +             return;
> > +
> > +     kcb = get_kprobe_ctlblk();
> > +     if (kprobe_running()) {
> > +             kprobes_inc_nmissed_count(p);
> > +     } else {
> > +             unsigned long orig_ip = instruction_pointer(regs);
> > +             /* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */
> > +             instruction_pointer_set(regs, ip + sizeof(kprobe_opcode_t));
> > +
> > +             __this_cpu_write(current_kprobe, p);
> > +             kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> > +             if (!p->pre_handler || !p->pre_handler(p, regs)) {
> > +                     /*
> > +                      * Emulate singlestep (and also recover regs->ip)
> > +                      * as if there is a 5byte nop
> > +                      */
> > +                     instruction_pointer_set(regs,
> > +                             (unsigned long)p->addr + MCOUNT_INSN_SIZE);
> > +                     if (unlikely(p->post_handler)) {
> > +                             kcb->kprobe_status = KPROBE_HIT_SSDONE;
> > +                             p->post_handler(p, regs, 0);
> > +                     }
> > +                     instruction_pointer_set(regs, orig_ip);
> > +             }
> > +             /*
> > +              * If pre_handler returns !0, it changes regs->ip. We have to
> > +              * skip emulating post_handler.
> > +              */
> > +             __this_cpu_write(current_kprobe, NULL);
> > +     }
> > +}
> > +NOKPROBE_SYMBOL(kprobe_ftrace_handler);
> > +
> >  static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
> >       .func = kprobe_ftrace_handler,
> >       .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY,
> > --
> > 2.23.0.rc1
> >  
> 
> 
> --
> Masami Hiramatsu <[email-masked]>

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