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>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index b6dc9d838a9a..35148b46c4f5 100644
--- 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();