[PATCH v5 10/10] powerpc/signal64: Use __get_user() to copy sigset_t

[Christophe Leroy]

"Christopher M. Riedl" <cmr at codefail.de> a écrit :

> Usually sigset_t is exactly 8B which is a "trivial" size and does not
> warrant using __copy_from_user(). Use __get_user() directly in
> anticipation of future work to remove the trivial size optimizations
> from __copy_from_user(). Calling __get_user() also results in a small
> boost to signal handling throughput here.
>
> Signed-off-by: Christopher M. Riedl <cmr at codefail.de>
> ---
>  arch/powerpc/kernel/signal_64.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kernel/signal_64.c  
> b/arch/powerpc/kernel/signal_64.c
> index 817b64e1e409..42fdc4a7ff72 100644
> --- a/arch/powerpc/kernel/signal_64.c
> +++ b/arch/powerpc/kernel/signal_64.c
> @@ -97,6 +97,14 @@ static void prepare_setup_sigcontext(struct  
> task_struct *tsk, int ctx_has_vsx_re
>  #endif /* CONFIG_VSX */
>  }
>
> +static inline int get_user_sigset(sigset_t *dst, const sigset_t *src)

Should be called __get_user_sigset() as it is a helper for __get_user()

> +{
> +	if (sizeof(sigset_t) <= 8)

We should always use __get_user(), see below.

> +		return __get_user(dst->sig[0], &src->sig[0]);

I think the above will not work on ppc32, it will only copy 4 bytes.
You must cast the source to u64*

> +	else
> +		return __copy_from_user(dst, src, sizeof(sigset_t));

I see no point in keeping this alternative. Today sigset_ t is fixed.
If you fear one day someone might change it to something different  
than a u64, just add a BUILD_BUG_ON(sizeof(sigset_t) != sizeof(u64));

> +}
> +
>  /*
>   * Set up the sigcontext for the signal frame.
>   */
> @@ -701,8 +709,9 @@ SYSCALL_DEFINE3(swapcontext, struct ucontext  
> __user *, old_ctx,
>  	 * We kill the task with a SIGSEGV in this situation.
>  	 */
>
> -	if (__copy_from_user(&set, &new_ctx->uc_sigmask, sizeof(set)))
> +	if (get_user_sigset(&set, &new_ctx->uc_sigmask))
>  		do_exit(SIGSEGV);
> +

This white space is not part of the change, keep patches to the  
minimum, avoid cosmetic

>  	set_current_blocked(&set);
>
>  	if (!user_read_access_begin(new_ctx, ctx_size))
> @@ -740,8 +749,9 @@ SYSCALL_DEFINE0(rt_sigreturn)
>  	if (!access_ok(uc, sizeof(*uc)))
>  		goto badframe;
>
> -	if (__copy_from_user(&set, &uc->uc_sigmask, sizeof(set)))
> +	if (get_user_sigset(&set, &uc->uc_sigmask))
>  		goto badframe;
> +

Same

>  	set_current_blocked(&set);
>
>  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> --
> 2.26.1