uprobes: allow ignoring of probe hits

Allow arches to decided to ignore a probe hit.  ARM will use this to
only call handlers if the conditions to execute a conditionally executed
instruction are satisfied.
Signed-off-by: David A. Long <dave.long@linaro.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>

include/linux/uprobes.h

@@ -126,6 +126,7 @@ extern bool arch_uprobe_xol_was_trapped(struct task_struct *tsk);
 extern int  arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data);
 extern void arch_uprobe_abort_xol(struct arch_uprobe *aup, struct pt_regs *regs);
 extern unsigned long arch_uretprobe_hijack_return_addr(unsigned long trampoline_vaddr, struct pt_regs *regs);
+extern bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs);
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
 };

kernel/events/uprobes.c

@@ -1804,6 +1804,11 @@ static bool handle_trampoline(struct pt_regs *regs)
 	return true;
 }
 
+bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs)
+{
+	return false;
+}
+
 /*
  * Run handler and ask thread to singlestep.
  * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
@@ -1858,7 +1863,11 @@ static void handle_swbp(struct pt_regs *regs)
 	if (!get_utask())
 		goto out;
 
+	if (arch_uprobe_ignore(&uprobe->arch, regs))
+		goto out;
+
 	handler_chain(uprobe, regs);
+
 	if (can_skip_sstep(uprobe, regs))
 		goto out;