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

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

[Jisheng Zhang]

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.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.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

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

[Masami Hiramatsu]

Hi Jisheng,

On Mon, 12 Apr 2021 17:41:01 +0800
Jisheng Zhang <Jisheng.Zhang@synaptics.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.

Hmm, RISC-V and other code also needs same fix.

Thank you,

> 
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.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@kernel.org>

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@kernel.org> wrote:

> Hi Jisheng,
> 
> On Mon, 12 Apr 2021 17:41:01 +0800
> Jisheng Zhang <Jisheng.Zhang@synaptics.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@kernel.org>

Thanks!

> 
> Hmm, RISC-V and other code also needs same fix.
> 
> Thank you,
> 
> > 
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.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@kernel.org>


-- 
Masami Hiramatsu <mhiramat@kernel.org>

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

[Will Deacon]

On Mon, 12 Apr 2021 17:41:01 +0800, Jisheng Zhang 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.
> 
> [...]

Applied to arm64 (for-next/fixes), thanks!

[1/1] arm64: kprobes: Restore local irqflag if kprobes is cancelled
      https://git.kernel.org/arm64/c/738fa58ee132

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev