x86: fix singlestep handling in reenter_kprobe

Highlight peculiar cases in singles-step kprobe handling.

In reenter_kprobe(), a breakpoint in KPROBE_HIT_SS case can only occur
when single-stepping a breakpoint on which a probe was installed. Since
such probes are single-stepped inline, identifying these cases is
unambiguous. All other cases leading up to KPROBE_HIT_SS are possible
bugs. Identify and WARN_ON such cases.

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index edc0a8e..f7ddbb8 100644 (file)
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -443,17 +443,6 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
        *sara = (unsigned long) &kretprobe_trampoline;
 }
 
-static void __kprobes recursive_singlestep(struct kprobe *p,
-                                          struct pt_regs *regs,
-                                          struct kprobe_ctlblk *kcb)
-{
-       save_previous_kprobe(kcb);
-       set_current_kprobe(p, regs, kcb);
-       kprobes_inc_nmissed_count(p);
-       prepare_singlestep(p, regs);
-       kcb->kprobe_status = KPROBE_REENTER;
-}
-
 static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs,
                                       struct kprobe_ctlblk *kcb)
 {
@@ -492,20 +481,29 @@ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
                break;
 #endif
        case KPROBE_HIT_ACTIVE:
-               recursive_singlestep(p, regs, kcb);
+               save_previous_kprobe(kcb);
+               set_current_kprobe(p, regs, kcb);
+               kprobes_inc_nmissed_count(p);
+               prepare_singlestep(p, regs);
+               kcb->kprobe_status = KPROBE_REENTER;
                break;
        case KPROBE_HIT_SS:
-               if (*p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
+               if (p == kprobe_running()) {
                        regs->flags &= ~TF_MASK;
                        regs->flags |= kcb->kprobe_saved_flags;
                        return 0;
                } else {
-                       recursive_singlestep(p, regs, kcb);
+                       /* A probe has been hit in the codepath leading up
+                        * to, or just after, single-stepping of a probed
+                        * instruction. This entire codepath should strictly
+                        * reside in .kprobes.text section. Raise a warning
+                        * to highlight this peculiar case.
+                        */
                }
-               break;
        default:
                /* impossible cases */
                WARN_ON(1);
+               return 0;
        }
 
        return 1;