arm: kprobes: Allow to handle reentered kprobe on single-stepping

This is arm port of commit 6a5022a56ac3 ("kprobes/x86: Allow to
handle reentered kprobe on single-stepping")

Since the FIQ handlers can interrupt in the single stepping
(or preparing the single stepping, do_debug etc.), we should
consider a kprobe is hit in the NMI handler. Even in that
case, the kprobe is allowed to be reentered as same as the
kprobes hit in kprobe handlers
(KPROBE_HIT_ACTIVE or KPROBE_HIT_SSDONE).

The real issue will happen when a kprobe hit while another
reentered kprobe is processing (KPROBE_REENTER), because
we already consumed a saved-area for the previous kprobe.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Jon Medhurst <tixy@linaro.org>

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index b6dc9d838a9a39b9ff2e22e9ed371a522ead0fa7..35148b46c4f5ed79c786cf731242284e40b98e91 100644 (file)
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -271,6 +271,7 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
                        switch (kcb->kprobe_status) {
                        case KPROBE_HIT_ACTIVE:
                        case KPROBE_HIT_SSDONE:
+                       case KPROBE_HIT_SS:
                                /* A pre- or post-handler probe got us here. */
                                kprobes_inc_nmissed_count(p);
                                save_previous_kprobe(kcb);
@@ -279,6 +280,11 @@ void __kprobes kprobe_handler(struct pt_regs *regs)
                                singlestep(p, regs, kcb);
                                restore_previous_kprobe(kcb);
                                break;
+                       case KPROBE_REENTER:
+                               /* A nested probe was hit in FIQ, it is a BUG */
+                               pr_warn("Unrecoverable kprobe detected at %p.\n",
+                                       p->addr);
+                               /* fall through */
                        default:
                                /* impossible cases */
                                BUG();