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Commit 829e9245 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Ingo Molnar
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kprobes/x86: Fix removed int3 checking order 



Fix kprobe/x86 to check removed int3 when failing to get kprobe
from hlist. Since we have a time window between checking int3
exists on probed address and getting kprobe on that address,
we can have following scenario:

 -------
 CPU1                     CPU2
 hit int3
 check int3 exists
                          remove int3
                          remove kprobe from hlist
 get kprobe from hlist
 no kprobe->OOPS!
 -------

This patch moves int3 checking if there is no kprobe on that
address for fixing this problem as follows:

 ------
 CPU1                     CPU2
 hit int3
                          remove int3
                          remove kprobe from hlist
 get kprobe from hlist
 no kprobe->check int3 exists
          ->rollback&retry
 ------

Signed-off-by: default avatarMasami Hiramatsu <mhiramat@redhat.com>
Acked-by: default avatarAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100427223348.2322.9112.stgit@localhost6.localdomain6>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent de068ec0

arch/x86/kernel/kprobes.c

+13 −14
Original line number Diff line number Diff line
@@ -534,20 +534,6 @@ static int __kprobes kprobe_handler(struct pt_regs *regs) 
	struct kprobe_ctlblk *kcb;



	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));

	if (*addr != BREAKPOINT_INSTRUCTION) {

		/*

		 * The breakpoint instruction was removed right

		 * after we hit it.  Another cpu has removed

		 * either a probepoint or a debugger breakpoint

		 * at this address.  In either case, no further

		 * handling of this interrupt is appropriate.

		 * Back up over the (now missing) int3 and run

		 * the original instruction.

		 */

		regs->ip = (unsigned long)addr;

		return 1;

	}



	/*

	 * We don't want to be preempted for the entire

	 * duration of kprobe processing. We conditionally
@@ -579,6 +565,19 @@ static int __kprobes kprobe_handler(struct pt_regs *regs) 
				setup_singlestep(p, regs, kcb, 0);

			return 1;

		}

	} else if (*addr != BREAKPOINT_INSTRUCTION) {

		/*

		 * The breakpoint instruction was removed right

		 * after we hit it.  Another cpu has removed

		 * either a probepoint or a debugger breakpoint

		 * at this address.  In either case, no further

		 * handling of this interrupt is appropriate.

		 * Back up over the (now missing) int3 and run

		 * the original instruction.

		 */

		regs->ip = (unsigned long)addr;

		preempt_enable_no_resched();

		return 1;

	} else if (kprobe_running()) {

		p = __get_cpu_var(current_kprobe);

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