lkml.org 
[lkml]   [2017]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: __user with scalar data types
On Mon, Jun 19, 2017 at 10:15:09AM -0600, Jordan Crouse wrote:
> A number of us over in DRM land have been using __u64 scalar types
> to store pointers for uapi structures in accordance with Daniel Vetter's
> now classic treatise on ioctls:
>
> http://blog.ffwll.ch/2013/11/botching-up-ioctls.html
>
> A smaller number of us have further been marking the __u64 with __user,
> to wit:
>
> struct uapistruct {
> ...
> __u64 __user myptr;
> ---
> };

It wouldn't make sense to have this:
struct uapistruct {
__u64 __user myptr;
__u64 anothermember;
};
In other words, eiter all members are in the user address space
or none are. So, a struct member should not be marked __user
(exactly as for 'const' or 'volatile').

It wouldn't also make sense to move the __user to the whole struct,
giving something like:
struct uapistruct {
__u64 myptr;
__u64 anothermember;
} __user;
because it's not the type that belong to the user address space
but some specific objects.

Of course, your real problem here is that you're using a __u64 to
store a pointer and then expect this __u64 to have some properties
unique to pointers.


-- Luc Van Oostenryck (sparse hacker)

\
 
 \ /
  Last update: 2017-06-19 21:31    [W:1.225 / U:0.712 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site