Re: [BUGFIX PATCH 1/3] kprobes/arm: Allow to handle reentered kprobe on single-stepping

[Masami Hiramatsu]

On Tue, 14 Feb 2017 10:01:43 +0000
"Jon Medhurst (Tixy)" <tixy@xxxxxxxxxx> wrote:

> On Tue, 2017-02-14 at 00:03 +0900, Masami Hiramatsu wrote:
> > This is arm port of commit 6a5022a56ac3 ("kprobes/x86: Allow to
> > handle reentered kprobe on single-stepping")
> > 
> > Since the FIQ handlers can interrupt in the single stepping
> > (or preparing the single stepping, do_debug etc.), we should
> > consider a kprobe is hit in the NMI handler. Even in that
> > case, the kprobe is allowed to be reentered as same as the
> > kprobes hit in kprobe handlers
> > (KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE).
> > 
> > The real issue will happen when a kprobe hit while another
> 
> Could to with 'is' being inserted above  ^^^
> (I know this is a copy of the x86 commit message)

Ah! yes, it should be corrected. 
> 
> > reentered kprobe is processing (KPROBE_REENTER), because
> > we already consumed a saved-area for the previous kprobe.
> > 
> > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > ---
> 
> Acked-by: Jon Medhurst <tixy@xxxxxxxxxx>

Thank you!

> 
> >  arch/arm/probes/kprobes/core.c |    6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> > index a4ec240..264fedb 100644
> > --- a/arch/arm/probes/kprobes/core.c
> > +++ b/arch/arm/probes/kprobes/core.c
> > @@ -270,6 +270,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
> >  			switch (kcb->kprobe_status) {
> >  			case KPROBE_HIT_ACTIVE:
> >  			case KPROBE_HIT_SSDONE:
> > +			case KPROBE_HIT_SS:
> >  				/* A pre- or post-handler probe got us here. */
> >  				kprobes_inc_nmissed_count(p);
> >  				save_previous_kprobe(kcb);
> > @@ -278,6 +279,11 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
> >  				singlestep(p, regs, kcb);
> >  				restore_previous_kprobe(kcb);
> >  				break;
> > +			case KPROBE_REENTER:
> > +				/* A nested probe was hit in FIQ, it is a BUG */
> > +				pr_warn("Unrecoverable kprobe detected at %p.\n",
> > +					p->addr);
> > +				/* fall through */
> >  			default:
> >  				/* impossible cases */
> >  				BUG();
> > 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>