x86: kprobes change kprobe_handler flow

Signed-off-by: Abhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: Quentin Barnes <qbarnes@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 711fec8..53ba6a5 100644 (file)
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -442,6 +442,34 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
        /* Replace the return addr with trampoline addr */
        *sara = (unsigned long) &kretprobe_trampoline;
 }
+
+static void __kprobes recursive_singlestep(struct kprobe *p,
+                                          struct pt_regs *regs,
+                                          struct kprobe_ctlblk *kcb)
+{
+       save_previous_kprobe(kcb);
+       set_current_kprobe(p, regs, kcb);
+       kprobes_inc_nmissed_count(p);
+       prepare_singlestep(p, regs);
+       kcb->kprobe_status = KPROBE_REENTER;
+}
+
+static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs,
+                                      struct kprobe_ctlblk *kcb)
+{
+#if !defined(CONFIG_PREEMPT) || defined(CONFIG_PM)
+       if (p->ainsn.boostable == 1 && !p->post_handler) {
+               /* Boost up -- we can execute copied instructions directly */
+               reset_current_kprobe();
+               regs->ip = (unsigned long)p->ainsn.insn;
+               preempt_enable_no_resched();
+               return;
+       }
+#endif
+       prepare_singlestep(p, regs);
+       kcb->kprobe_status = KPROBE_HIT_SS;
+}
+
 /*
  * We have reentered the kprobe_handler(), since another probe was hit while
  * within the handler. We save the original kprobes variables and just single
@@ -450,13 +478,9 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
                                    struct kprobe_ctlblk *kcb)
 {
-       if (kcb->kprobe_status == KPROBE_HIT_SS &&
-           *p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
-               regs->flags &= ~X86_EFLAGS_TF;
-               regs->flags |= kcb->kprobe_saved_flags;
-               return 0;
+       switch (kcb->kprobe_status) {
+       case KPROBE_HIT_SSDONE:
 #ifdef CONFIG_X86_64
-       } else if (kcb->kprobe_status == KPROBE_HIT_SSDONE) {
                /* TODO: Provide re-entrancy from post_kprobes_handler() and
                 * avoid exception stack corruption while single-stepping on
                 * the instruction of the new probe.
@@ -464,14 +488,26 @@ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
                arch_disarm_kprobe(p);
                regs->ip = (unsigned long)p->addr;
                reset_current_kprobe();
-               return 1;
+               preempt_enable_no_resched();
+               break;
 #endif
+       case KPROBE_HIT_ACTIVE:
+               recursive_singlestep(p, regs, kcb);
+               break;
+       case KPROBE_HIT_SS:
+               if (*p->ainsn.insn == BREAKPOINT_INSTRUCTION) {
+                       regs->flags &= ~TF_MASK;
+                       regs->flags |= kcb->kprobe_saved_flags;
+                       return 0;
+               } else {
+                       recursive_singlestep(p, regs, kcb);
+               }
+               break;
+       default:
+               /* impossible cases */
+               WARN_ON(1);
        }
-       save_previous_kprobe(kcb);
-       set_current_kprobe(p, regs, kcb);
-       kprobes_inc_nmissed_count(p);
-       prepare_singlestep(p, regs);
-       kcb->kprobe_status = KPROBE_REENTER;
+
        return 1;
 }
 
@@ -481,83 +517,66 @@ static int __kprobes reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
  */
 static int __kprobes kprobe_handler(struct pt_regs *regs)
 {
-       struct kprobe *p;
-       int ret = 0;
        kprobe_opcode_t *addr;
+       struct kprobe *p;
        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
+        * duration of kprobe processing. We conditionally
+        * re-enable preemption at the end of this function,
+        * and also in reenter_kprobe() and setup_singlestep().
         */
        preempt_disable();
-       kcb = get_kprobe_ctlblk();
 
+       kcb = get_kprobe_ctlblk();
        p = get_kprobe(addr);
+
        if (p) {
-               /* Check we're not actually recursing */
                if (kprobe_running()) {
-                       ret = reenter_kprobe(p, regs, kcb);
-                       if (kcb->kprobe_status == KPROBE_REENTER)
-                       {
-                               ret = 1;
-                               goto out;
-                       }
-                       goto preempt_out;
+                       if (reenter_kprobe(p, regs, kcb))
+                               return 1;
                } else {
                        set_current_kprobe(p, regs, kcb);
                        kcb->kprobe_status = KPROBE_HIT_ACTIVE;
-                       if (p->pre_handler && p->pre_handler(p, regs))
-                       {
-                               /* handler set things up, skip ss setup */
-                               ret = 1;
-                               goto out;
-                       }
-               }
-       } 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.
+                        * If we have no pre-handler or it returned 0, we
+                        * continue with normal processing.  If we have a
+                        * pre-handler and it returned non-zero, it prepped
+                        * for calling the break_handler below on re-entry
+                        * for jprobe processing, so get out doing nothing
+                        * more here.
                         */
-                       regs->ip = (unsigned long)addr;
-                       ret = 1;
-                       goto preempt_out;
+                       if (!p->pre_handler || !p->pre_handler(p, regs))
+                               setup_singlestep(p, regs, kcb);
+                       return 1;
                }
-               if (kprobe_running()) {
-                       p = __get_cpu_var(current_kprobe);
-                       if (p->break_handler && p->break_handler(p, regs))
-                               goto ss_probe;
+       } else if (kprobe_running()) {
+               p = __get_cpu_var(current_kprobe);
+               if (p->break_handler && p->break_handler(p, regs)) {
+                       setup_singlestep(p, regs, kcb);
+                       return 1;
                }
-               /* Not one of ours: let kernel handle it */
-               goto preempt_out;
-       }
+       } /* else: not a kprobe fault; let the kernel handle it */
 
-ss_probe:
-       ret = 1;
-#if !defined(CONFIG_PREEMPT) || defined(CONFIG_PM)
-       if (p->ainsn.boostable == 1 && !p->post_handler) {
-               /* Boost up -- we can execute copied instructions directly */
-               reset_current_kprobe();
-               regs->ip = (unsigned long)p->ainsn.insn;
-               goto preempt_out;
-       }
-#endif
-       prepare_singlestep(p, regs);
-       kcb->kprobe_status = KPROBE_HIT_SS;
-       goto out;
-
-preempt_out:
        preempt_enable_no_resched();
-out:
-       return ret;
+       return 0;
 }
 
 /*