Le 11/12/2021 à 18:53, David Laight a écrit :

From: Tiezhu Yang

quoted

Sent: 11 December 2021 03:33

v2:
   -- add copy_to_user_or_kernel() in lib/usercopy.c
   -- define userbuf as bool type

Instead of having a flag to indicate whether the buffer is user or kernel,
would it be better to have two separate buffer pointers.
One for a user space buffer, the other for a kernel space buffer.
Exactly one of the buffers should always be NULL.

That way the flag is never incorrectly set.

It's a very good idea.

I was worried about the casts forcing the __user property away and back. 
With that approach we will preserve the __user tags on user buffers and 
enable sparse checking.

The only little drawback I see is that apparently GCC doesn't consider 
the NULL value as a constant and therefore doesn't perform constant 
folding on pointers. Not sure if this is a problem here.

Christophe