Re: [patch V4 06/12] s390/uaccess: Use unsafe wrappers for ASM GOTO

Heiko Carstens
2025-10-22T15:02:07Z

On Wed, Oct 22, 2025 at 02:49:09PM +0200, Thomas Gleixner wrote:
> ASM GOTO is miscompiled by GCC when it is used inside a auto cleanup scope:
>
> bool foo(u32 __user *p, u32 val)
> {
> scoped_guard(pagefault)
> unsafe_put_user(val, p, efault);
> return true;
> efault:
> return false;
> }
>
> It ends up leaking the pagefault disable counter in the fault path. clang
> at least fails the build.
>
> S390 is not affected for unsafe_*_user() as it uses it's own local label
> already, but __get/put_kernel_nofault() lack that.
>
> Rename them to arch_*_kernel_nofault() which makes the generic uaccess
> header wrap it with a local label that makes both compilers emit correct
> code.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
> Cc: Sven Schnelle <svens@linux.ibm.com>
> Cc: linux-s390@vger.kernel.org
> ---
> arch/s390/include/asm/uaccess.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)

Acked-by: Heiko Carstens <hca@linux.ibm.com>