[PATCH] powerpc: Add barrier_nospec to raw_copy_in_user()

[Michal Suchánek]

On Wed,  6 Mar 2019 12:10:38 +1100
Suraj Jitindar Singh <sjitindarsingh at gmail.com> wrote:

> Commit ddf35cf3764b ("powerpc: Use barrier_nospec in copy_from_user()")
> Added barrier_nospec before loading from user-controller pointers.
> The intention was to order the load from the potentially user-controlled
> pointer vs a previous branch based on an access_ok() check or similar.
> 
> In order to achieve the same result, add a barrier_nospec to the
> raw_copy_in_user() function before loading from such a user-controlled
> pointer.
> 
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh at gmail.com>
> ---
>  arch/powerpc/include/asm/uaccess.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index e3a731793ea2..bb615592d5bb 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -306,6 +306,7 @@ extern unsigned long __copy_tofrom_user(void __user *to,
>  static inline unsigned long
>  raw_copy_in_user(void __user *to, const void __user *from, unsigned long n)
>  {
> +	barrier_nospec();
>  	return __copy_tofrom_user(to, from, n);
>  }
>  #endif /* __powerpc64__ */

Hello,

AFAICT this is not needed. The data cannot be used in the kernel without
subsequent copy_from_user which already has the nospec barrier.

Thanks

Michal