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Message-Id: <20210412234643.08a0a8578fb456190c50bc70@kernel.org>
Date: Mon, 12 Apr 2021 23:46:43 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Liao Chang <liaochang1@...wei.com>
Subject: Re: [PATCH] arm64: kprobes: Restore local irqflag if kprobes is
cancelled
On Mon, 12 Apr 2021 22:11:44 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:
> Hi Jisheng,
>
> On Mon, 12 Apr 2021 17:41:01 +0800
> Jisheng Zhang <Jisheng.Zhang@...aptics.com> 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@...nel.org>
Thanks!
>
> Hmm, RISC-V and other code also needs same fix.
>
> Thank you,
>
> >
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> > ---
> > 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@...nel.org>
--
Masami Hiramatsu <mhiramat@...nel.org>
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