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

Thomas Gleixner
2025-10-22T12:49:15Z

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(-)

--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -468,8 +468,8 @@ do { \

#endif /* CONFIG_CC_HAS_ASM_GOTO_OUTPUT && CONFIG_CC_HAS_ASM_AOR_FORMAT_FLAGS */

-#define __get_kernel_nofault __mvc_kernel_nofault
-#define __put_kernel_nofault __mvc_kernel_nofault
+#define arch_get_kernel_nofault __mvc_kernel_nofault
+#define arch_put_kernel_nofault __mvc_kernel_nofault

void __cmpxchg_user_key_called_with_bad_pointer(void);