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

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Date:   Tue, 14 Feb 2017 10:01:43 +0000
From:   "Jon Medhurst (Tixy)" <tixy@...aro.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Russell King <linux@...linux.org.uk>
Cc:     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 1/3] kprobes/arm: Allow to handle reentered
 kprobe on single-stepping

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)

> reentered kprobe is processing (KPROBE_REENTER), because
> we already consumed a saved-area for the previous kprobe.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---

Acked-by: Jon Medhurst <tixy@...aro.org>

>  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();
>