Re: [PATCH v26 23/30] x86/cet/shstk: Handle thread shadow stack

On 5/10/2021 7:15 AM, Borislav Petkov wrote:

On Tue, Apr 27, 2021 at 01:43:08PM -0700, Yu-cheng Yu wrote:

quoted

@@ -181,6 +184,12 @@ int copy_thread(unsigned long clone_flags, unsigned long sp, unsigned long arg,
  	if (clone_flags & CLONE_SETTLS)
  		ret = set_new_tls(p, tls);
  
+#ifdef CONFIG_X86_64

IS_ENABLED

quoted

+	/* Allocate a new shadow stack for pthread */
+	if (!ret)
+		ret = shstk_setup_thread(p, clone_flags, stack_size);
+#endif
+

And why is this addition here...

quoted

  	if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
  		io_bitmap_share(p);

... instead of here?

<---

io_bitmap_share() does refcount_inc(&current->thread.io_bitmap->refcnt), 
and the function won't fail.  However, shadow stack allocation can fail. 
  So, maybe leave io_bitmap_share() at the end?

Thanks,
Yu-cheng