arm64: kprobes: WARN if attempting to step with PSTATE.D=1

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@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 9c70e88..c89811d 100644 (file)
--- 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);