Commit fb8830e7 authored by Abhishek Sagar's avatar Abhishek Sagar Committed by Ingo Molnar
Browse files

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: default avatarAbhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 0723a69a

arch/x86/kernel/kprobes.c

+13 −15
Original line number Diff line number Diff line
@@ -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;

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