uprobes/x86: Don't use arch_uprobe_abort_xol() in arch_uprobe_post_xol()

014940bad8e4 "uprobes/x86: Send SIGILL if arch_uprobe_post_xol() fails"
changed arch_uprobe_post_xol() to use arch_uprobe_abort_xol() if ->post_xol
fails. This was correct and helped to avoid the additional complications,
we need to clear X86_EFLAGS_TF in this case.

However, now that we have uprobe_xol_ops->abort() hook it would be better
to avoid arch_uprobe_abort_xol() here. ->post_xol() should likely do what
->abort() does anyway, we should not do the same work twice. Currently only
handle_riprel_post_xol() can be called twice, this is unnecessary but safe.
Still this is not clean and can lead to the problems in future.

Change arch_uprobe_post_xol() to clear X86_EFLAGS_TF and restore ->ip by
hand and avoid arch_uprobe_abort_xol(). This temporary uglifies the usage
of autask.saved_tf, we will cleanup this later.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>

1 files changed, 9 insertions, 8 deletions

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index b3c2a92cce6c..2efb93f96030 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -759,22 +759,24 @@ 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);
+        current->thread.trap_nr = utask->autask.saved_trap_nr;
 
         if (auprobe->ops->post_xol) {
                 int err = auprobe->ops->post_xol(auprobe, regs);
                 if (err) {
-                        arch_uprobe_abort_xol(auprobe, regs);
+                        if (!utask->autask.saved_tf)
+                                regs->flags &= ~X86_EFLAGS_TF;
                         /*
-                         * Restart the probed insn. ->post_xol() must ensure
-                         * this is really possible if it returns -ERESTART.
+                         * Restore ->ip for restart or post mortem analysis.
+                         * ->post_xol() must not return -ERESTART unless this
+                         * is really possible.
                          */
+                        regs->ip = utask->vaddr;
                         if (err == -ERESTART)
                                 return 0;
                         return err;
                 }
         }
-
-        current->thread.trap_nr = utask->autask.saved_trap_nr;
         /*
          * arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP
          * so we can get an extra SIGTRAP if we do not clear TF. We need
@@ -819,9 +821,8 @@ 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, or if arch_uprobe_post_xol() failed.
- * Reset the instruction pointer to its probed address for the potential
- * restart or for post mortem analysis.
+ * the thread has a fatal signal. 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)
 {