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: Fengguang 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: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 29 insertions, 13 deletions

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index f49f60cca40d..b7c2a85d1926 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -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)) {
-                        /*
-                         * 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);
+                if (!p->pre_handler || !p->pre_handler(p, regs))
+                        skip_singlestep(p, regs, kcb);
+                /*
+                 * If pre_handler returns !0, it sets regs->ip and
+                 * resets current kprobe.
+                 */
         }
 end:
         local_irq_restore(flags);