linux-kernel - Re: [BUGFIX PATCH 2/3] kprobes/arm: Skip single-stepping in recursing path if possible

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Message-Id: <20170215003140.c30510159fd6b951e80871ac@kernel.org>
Date:   Wed, 15 Feb 2017 00:31:40 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     "Jon Medhurst (Tixy)" <tixy@...aro.org>
Cc:     Russell King <linux@...linux.org.uk>, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H . Peter Anvin" <hpa@...or.com>, Wang Nan <wangnan0@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        "David A . Long" <dave.long@...aro.org>,
        Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>
Subject: Re: [BUGFIX PATCH 2/3] kprobes/arm: Skip single-stepping in
 recursing path if possible

On Tue, 14 Feb 2017 10:07:17 +0000
"Jon Medhurst (Tixy)" <tixy@...aro.org> wrote:

> On Tue, 2017-02-14 at 00:04 +0900, Masami Hiramatsu wrote:
> > Kprobes/arm skips single-stepping (moreover handling the event)
> > if the conditional instruction must not be executed. This
> > also apply the rule when we hit the recursing kprobe, so
> > that kprobe does not count nmissed up in that case.
> 
> Perhaps that last sentence would read better if written something like:
> 
> "This also applies that rule when we hit a recursing kprobe, so that the
> nmissed count isn't incremented in that case."

OK, Thanks!

> 
> 
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> 
> Acked-by: Jon Medhurst <tixy@...aro.org>
> 
> > ---
> >  arch/arm/probes/kprobes/core.c |   19 ++++++++++---------
> >  1 file changed, 10 insertions(+), 9 deletions(-)
> > 
> > diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
> > index 264fedb..84989ae 100644
> > --- a/arch/arm/probes/kprobes/core.c
> > +++ b/arch/arm/probes/kprobes/core.c
> > @@ -265,7 +265,15 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
> >  #endif
> >  
> >  	if (p) {
> > -		if (cur) {
> > +		if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
> > +			/*
> > +			 * Probe hit but conditional execution check failed,
> > +			 * so just skip the instruction and continue as if
> > +			 * nothing had happened.
> > +			 * In this case, we can skip recursing check too.
> > +			 */
> > +			singlestep_skip(p, regs);
> > +		} else if (cur) {
> >  			/* Kprobe is pending, so we're recursing. */
> >  			switch (kcb->kprobe_status) {
> >  			case KPROBE_HIT_ACTIVE:
> > @@ -288,7 +296,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
> >  				/* impossible cases */
> >  				BUG();
> >  			}
> > -		} else if (p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
> > +		} else {
> >  			/* Probe hit and conditional execution check ok. */
> >  			set_current_kprobe(p);
> >  			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> > @@ -309,13 +317,6 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
> >  				}
> >  				reset_current_kprobe();
> >  			}
> > -		} else {
> > -			/*
> > -			 * Probe hit but conditional execution check failed,
> > -			 * so just skip the instruction and continue as if
> > -			 * nothing had happened.
> > -			 */
> > -			singlestep_skip(p, regs);
> >  		}
> >  	} else if (cur) {
> >  		/* We probably hit a jprobe.  Call its break handler. */
> > 


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