Re: [PATCH 4.4.y] arm: kprobes: Allow to handle reentered kprobe on single-stepping

[Xiaoming Ni]

On 2021/7/9 17:00, Masami Hiramatsu wrote:
> Hi Shaobo,
>
> Thanks for backporting!
> Greg, it seems this patch can be applied to 4.9 too without any issue.
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.9.y&id=355a04fa1fc23c4fb1d16440e62d46a42691e96b

The v4.9 branch has been fixed.

Thanks
Xiaoming Ni



> Thank you,
>
> On Fri, 9 Jul 2021 10:46:30 +0800
> Shaobo Huang <huangshaobo6@xxxxxxxxxx> wrote:
>
> > From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > Signed-off-by: Jon Medhurst <tixy@xxxxxxxxxx>
> > Fixes: 24ba613c9d6c ("ARM kprobes: core code")
> > Cc: stable@xxxxxxxxxxxxxxx #v2.6.25~v4.11
> > Signed-off-by: huangshaobo <huangshaobo6@xxxxxxxxxx>
> > ---
> >   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