[PATCH 3/4] arm64: kprobes: WARN if attempting to step with PSTATE.D=1

[Mark Rutland]

On Tue, Jul 19, 2016 at 03:07:39PM +0100, Will Deacon wrote:
> Stepping with PSTATE.D=1 is bad news. The step won't generate a debug
> exception and we'll likely walk off into random data structures. This
> should never happen, but when it does, it's a PITA to debug. Add a
> WARN_ON to shout if we realise this is about to take place.
> 
> Signed-off-by: Will Deacon <will.deacon at arm.com>

Acked-by: Mark Rutland <mark.rutland at arm.com>

Mark.

> ---
>  arch/arm64/kernel/probes/kprobes.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index 9c70e8812ea9..c89811d1e294 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -254,6 +254,8 @@ static void __kprobes setup_singlestep(struct kprobe *p,
>  
>  		if (kcb->kprobe_status == KPROBE_REENTER)
>  			spsr_set_debug_flag(regs, 0);
> +		else
> +			WARN_ON(regs->pstate & PSR_D_BIT);
>  
>  		/* IRQs and single stepping do not mix well. */
>  		kprobes_save_local_irqflag(kcb, regs);
> -- 
> 2.1.4
> 
> 
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