[PATCH 4.9.y] arm: kprobes: Allow to handle reentered kprobe on single-stepping

[Masami Hiramatsu]

Hi ShaoBo,

Thanks for backporting and real bug report!

On Wed, 3 Mar 2021 15:10:52 +0800
ShaoBo Huang <huangshaobo6 at huawei.com> wrote:

> From: Masami Hiramatsu <mhiramat at kernel.org>
> 
> commit f3fbd7ec62dec1528fb8044034e2885f2b257941 upstream
> 
> 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
> reentered kprobe is processing (KPROBE_REENTER), because
> we already consumed a saved-area for the previous kprobe.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat at kernel.org>
> Signed-off-by: Jon Medhurst <tixy at linaro.org>
> Fixes: 24ba613c9d6c ("ARM kprobes: core code")
> Cc: stable at vger.kernel.org #v2.6.25~v4.11
> Signed-off-by: huangshaobo <huangshaobo6 at huawei.com>
> ---
>  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 3eb018fa1a1f..c3362ddd6c4c 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();
> -- 
> 2.12.3
> 


-- 
Masami Hiramatsu <mhiramat at kernel.org>