kprobes/x86: Fix kprobes to collectly handle IP on ftrace

Current kprobe_ftrace_handler expects regs->ip == ip, but it is
incorrect (originally on x86-64). Actually, ftrace handler sets
regs->ip = ip + MCOUNT_INSN_SIZE.
kprobe_ftrace_handler must take care for that.

Link: http://lkml.kernel.org/r/20120905143112.10329.72069.stgit@localhost.localdomain
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: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 47ae1023a93c131b4e552b6c94f4a900e985b5a3..f49f60cca40db5b314b7c67dcfa81e99a3803b8f 100644 (file)
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -1072,7 +1072,8 @@ void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
        if (kprobe_running()) {
                kprobes_inc_nmissed_count(p);
        } else {
-               regs->ip += sizeof(kprobe_opcode_t);
+               /* 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;
@@ -1080,13 +1081,15 @@ void __kprobes kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
                        p->pre_handler(p, regs);
 
                if (unlikely(p->post_handler)) {
-                       /* Emulate singlestep as if there is a 5byte nop */
+                       /*
+                        * Emulate singlestep (and also recover regs->ip)
+                        * as if there is a 5byte nop
+                        */
                        regs->ip = ip + MCOUNT_INSN_SIZE;
                        kcb->kprobe_status = KPROBE_HIT_SSDONE;
                        p->post_handler(p, regs, 0);
                }
                __this_cpu_write(current_kprobe, NULL);
-               regs->ip = ip;  /* Recover for next callback */
        }
 end:
        local_irq_restore(flags);