Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit a017784f authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt
Browse files

kprobes/ftrace: Recover original IP if pre_handler doesn't change it 

Recover original IP register if the pre_handler doesn't change it.
Since current kprobes doesn't expect that another ftrace handler
may change regs->ip, it sets kprobe.addr + MCOUNT_INSN_SIZE to
regs->ip and returns to ftrace.
This seems wrong behavior since kprobes can recover regs->ip
and safely pass it to another handler.

This adds code which recovers original regs->ip passed from
ftrace right before returning to ftrace, so that another ftrace
user can change regs->ip.

Link: http://lkml.kernel.org/r/20141009130106.4698.26362.stgit@kbuild-f20.novalocal



Signed-off-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 0af26492

arch/x86/kernel/kprobes/ftrace.c

+6 −3
Original line number Diff line number Diff line
@@ -27,7 +27,7 @@ 


static nokprobe_inline

int __skip_singlestep(struct kprobe *p, struct pt_regs *regs,

		      struct kprobe_ctlblk *kcb)

		      struct kprobe_ctlblk *kcb, unsigned long orig_ip)

{

	/*

	 * Emulate singlestep (and also recover regs->ip)
@@ -39,6 +39,8 @@ int __skip_singlestep(struct kprobe *p, struct pt_regs *regs, 
		p->post_handler(p, regs, 0);

	}

	__this_cpu_write(current_kprobe, NULL);

	if (orig_ip)

		regs->ip = orig_ip;

	return 1;

}
@@ -46,7 +48,7 @@ int skip_singlestep(struct kprobe *p, struct pt_regs *regs, 
		    struct kprobe_ctlblk *kcb)

{

	if (kprobe_ftrace(p))

		return __skip_singlestep(p, regs, kcb);

		return __skip_singlestep(p, regs, kcb, 0);

	else

		return 0;

}
@@ -71,13 +73,14 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, 
	if (kprobe_running()) {

		kprobes_inc_nmissed_count(p);

	} else {

		unsigned long orig_ip = regs->ip;

		/* Kprobe handler expects regs->ip = ip + 1 as breakpoint hit */

		regs->ip = ip + sizeof(kprobe_opcode_t);



		__this_cpu_write(current_kprobe, p);

		kcb->kprobe_status = KPROBE_HIT_ACTIVE;

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

			__skip_singlestep(p, regs, kcb);

			__skip_singlestep(p, regs, kcb, orig_ip);

		/*

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

		 * resets current kprobe.