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

["Jon Medhurst (Tixy)" <tixy@linaro.org>]

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."


> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

Acked-by: Jon Medhurst <tixy@linaro.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. */
>