[PATCH 4.4.y] arm: kprobes: Allow to handle reentered kprobe on single-stepping

[Shaobo Huang]

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit f3fbd7ec62dec1528fb8044034e2885f2b257941 upstream

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@xxxxxxxxxx>
Signed-off-by: Jon Medhurst <tixy@xxxxxxxxxx>
Fixes: 24ba613c9d6c ("ARM kprobes: core code")
Cc: stable@xxxxxxxxxxxxxxx #v2.6.25~v4.11
Signed-off-by: huangshaobo <huangshaobo6@xxxxxxxxxx>
---
 arch/arm/probes/kprobes/core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index 3eb018fa1a1f..c3362ddd6c4c 100644
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -270,6 +270,7 @@ 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);
@@ -278,6 +279,11 @@ 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();
-- 
2.12.3