Re: [PATCH] arm64: kprobes: Restore local irqflag if kprobes is cancelled

[Masami Hiramatsu]

On Mon, 12 Apr 2021 22:11:44 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> Hi Jisheng,
> 
> On Mon, 12 Apr 2021 17:41:01 +0800
> Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> wrote:
> 
> > If instruction being single stepped caused a page fault, the kprobes
> > is cancelled to let the page fault handler continue as a normal page
> > fault. But the local irqflags are disabled so cpu will restore pstate
> > with DAIF masked. After pagefault is serviced, the kprobes is
> > triggerred again, we overwrite the saved_irqflag by calling
> > kprobes_save_local_irqflag(). NOTE, DAIF is masked in this new saved
> > irqflag. After kprobes is serviced, the cpu pstate is retored with
> > DAIF masked.
> > 
> > This patch is inspired by one patch for riscv from Liao Chang.
> 
> Thanks for pointing it out. But I think kprobes_restore_local_irqflag()
> is also needed for kcb->kprobe_status == KPROBE_REENTER case...no.
> This is more complicated. In the reenter case, I think we have to retry
> the kpreprobe_fault_handler() with recovered previous kprobes so that
> it can handle page fault in its handler.

Ah, this is another issue, and needs another fix.

So this patch itself is good to me.

Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Thanks!

> 
> Hmm, RISC-V and other code also needs same fix.
> 
> Thank you,
> 
> > 
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx>
> > ---
> >  arch/arm64/kernel/probes/kprobes.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> > index 66aac2881ba8..85645b2b0c7a 100644
> > --- a/arch/arm64/kernel/probes/kprobes.c
> > +++ b/arch/arm64/kernel/probes/kprobes.c
> > @@ -267,10 +267,12 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
> >  		if (!instruction_pointer(regs))
> >  			BUG();
> >  
> > -		if (kcb->kprobe_status == KPROBE_REENTER)
> > +		if (kcb->kprobe_status == KPROBE_REENTER) {
> >  			restore_previous_kprobe(kcb);
> > -		else
> > +		} else {
> > +			kprobes_restore_local_irqflag(kcb, regs);
> >  			reset_current_kprobe();
> > +		}
> >  
> >  		break;
> >  	case KPROBE_HIT_ACTIVE:
> > -- 
> > 2.31.0
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@xxxxxxxxxx>


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>