uprobes/x86: Send SIGILL if arch_uprobe_post_xol() fails

Currently the error from arch_uprobe_post_xol() is silently ignored.
This doesn't look good and this can lead to the hard-to-debug problems.

1. Change handle_singlestep() to loudly complain and send SIGILL.

   Note: this only affects x86, ppc/arm can't fail.

2. Change arch_uprobe_post_xol() to call arch_uprobe_abort_xol() and
   avoid TF games if it is going to return an error.

   This can help to to analyze the problem, if nothing else we should
   not report ->ip = xol_slot in the core-file.

   Note: this means that handle_riprel_post_xol() can be called twice,
   but this is fine because it is idempotent.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 08cdb82815fe..e72903eacd43 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -594,6 +594,15 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	struct uprobe_task *utask = current->utask;
 
 	WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
+
+	if (auprobe->ops->post_xol) {
+		int err = auprobe->ops->post_xol(auprobe, regs);
+		if (err) {
+			arch_uprobe_abort_xol(auprobe, regs);
+			return err;
+		}
+	}
+
 	current->thread.trap_nr = utask->autask.saved_trap_nr;
 	/*
 	 * arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP
@@ -605,8 +614,6 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	else if (!(auprobe->fixups & UPROBE_FIX_SETF))
 		regs->flags &= ~X86_EFLAGS_TF;
 
-	if (auprobe->ops->post_xol)
-		return auprobe->ops->post_xol(auprobe, regs);
 	return 0;
 }
 
@@ -641,8 +648,9 @@ int arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val,
 
 /*
  * This function gets called when XOL instruction either gets trapped or
- * the thread has a fatal signal, so reset the instruction pointer to its
- * probed address.
+ * the thread has a fatal signal, or if arch_uprobe_post_xol() failed.
+ * Reset the instruction pointer to its probed address for the potential
+ * restart or for post mortem analysis.
  */
 void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 {