Commit c6aaf4d0 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt
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kprobes/x86: Fix to support jprobes on ftrace-based kprobe 

Fix kprobes/x86 to support jprobes on ftrace-based kprobes.
Because of -mfentry support of ftrace, ftrace is now put
on the beginning of function where jprobes are put.

Originally ftrace-based kprobes doesn't support jprobe
because it will change regs->ip and ftrace doesn't support
changing IP and ftrace itself doesn't conflict jprobe.
However, ftrace -mfentry support moves mcount call on the
top of functions where jprobes are put. This means that
jprobe always conflicts with ftrace-based kprobe and fails.

This patch allows ftrace-based kprobes to support jprobes
by allowing to modify regs->ip and kprobes breakpoint
handler also allows to skip singlestepping because there
is a ftrace call (not an original instruction).

Link: http://lkml.kernel.org/r/20120905143125.10329.90836.stgit@localhost.localdomain



Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 47d5a5f8

arch/x86/kernel/kprobes.c

+29 −13
Original line number Diff line number Diff line
@@ -541,6 +541,8 @@ reenter_kprobe(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb 
	return 1;

}



static void __kprobes skip_singlestep(struct kprobe *p, struct pt_regs *regs,

				      struct kprobe_ctlblk *kcb);

/*

 * Interrupts are disabled on entry as trap3 is an interrupt gate and they

 * remain disabled throughout this function.
@@ -599,6 +601,12 @@ static int __kprobes kprobe_handler(struct pt_regs *regs) 
	} else if (kprobe_running()) {

		p = __this_cpu_read(current_kprobe);

		if (p->break_handler && p->break_handler(p, regs)) {

#ifdef KPROBES_CAN_USE_FTRACE

			if (kprobe_ftrace(p)) {

				skip_singlestep(p, regs, kcb);

				return 1;

			}

#endif

			setup_singlestep(p, regs, kcb, 0);

			return 1;

		}
@@ -1053,6 +1061,21 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) 
}



#ifdef KPROBES_CAN_USE_FTRACE

static void __kprobes skip_singlestep(struct kprobe *p, struct pt_regs *regs,

				      struct kprobe_ctlblk *kcb)

{

	/*

	 * Emulate singlestep (and also recover regs->ip)

	 * as if there is a 5byte nop

	 */

	regs->ip = (unsigned long)p->addr + MCOUNT_INSN_SIZE;

	if (unlikely(p->post_handler)) {

		kcb->kprobe_status = KPROBE_HIT_SSDONE;

		p->post_handler(p, regs, 0);

	}

	__this_cpu_write(current_kprobe, NULL);

}



/* Ftrace callback handler for kprobes */

void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,

				     struct ftrace_ops *ops, struct pt_regs *regs)
@@ -1077,19 +1100,12 @@ void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, 


		__this_cpu_write(current_kprobe, p);

		kcb->kprobe_status = KPROBE_HIT_ACTIVE;

		if (p->pre_handler)

			p->pre_handler(p, regs);



		if (unlikely(p->post_handler)) {

		if (!p->pre_handler || !p->pre_handler(p, regs))

			skip_singlestep(p, regs, kcb);

		/*

			 * Emulate singlestep (and also recover regs->ip)

			 * as if there is a 5byte nop

		 * If pre_handler returns !0, it sets regs->ip and

		 * resets current kprobe.

		 */

			regs->ip = ip + MCOUNT_INSN_SIZE;

			kcb->kprobe_status = KPROBE_HIT_SSDONE;

			p->post_handler(p, regs, 0);

		}

		__this_cpu_write(current_kprobe, NULL);

	}

end:

	local_irq_restore(flags);

kernel/kprobes.c

+0 −3
Original line number Diff line number Diff line
@@ -1418,9 +1418,6 @@ static __kprobes int check_kprobe_address_safe(struct kprobe *p, 
		/* Given address is not on the instruction boundary */

		if ((unsigned long)p->addr != ftrace_addr)

			return -EILSEQ;

		/* break_handler (jprobe) can not work with ftrace */

		if (p->break_handler)

			return -EINVAL;

		p->flags |= KPROBE_FLAG_FTRACE;

#else	/* !KPROBES_CAN_USE_FTRACE */

		return -EINVAL;

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