On Thu, Aug 30, 2018 at 4:41 AM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
>
> This patch adds __force annotations for __user pointers casts detected by
> sparse with the -Wcast-from-as flag enabled (added in [1]).
No, several of these are wrong, and just silence a warning that shows a problem.
So for example:
> static inline compat_uptr_t ptr_to_compat(void __user *uptr)
> {
> - return (u32)(unsigned long)uptr;
> + return (u32)(__force unsigned long)uptr;
> }
this actually looks correct.
But:
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -76,7 +76,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
> {
> unsigned long ret, limit = current_thread_info()->addr_limit;
>
> - __chk_user_ptr(addr);
> + __chk_user_ptr((void __force *)addr);
This looks actively wrong. The whole - and only - point of
"__chk_user_ptr()" is that it warns about a lack of a "__user *" type.
So the above makes no sense at all.
There are other similar "that makes no sense what-so-ever", like this one:
> - struct compat_group_req __user *gr32 = (void *)optval;
> + struct compat_group_req __user *gr32 = (__force void *)optval;
no, the additionl of __force is not the right thing, the problem, is
that a __user pointer is cast to a non-user 'void *' only to be
assigned to another user type.
The fix should have been to use (void __user *) as the cast instead,
no __force needed.
In general, I think the patch shows all the signs of "mindlessly just
add casts", which is exactly the wrong thing to do to sparse warnings.
Linus
