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

From: Heiko Carstens <hca@linux.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	"Christian Borntraeger" <borntraeger@linux.ibm.com>,
	"Sven Schnelle" <svens@linux.ibm.com>,
	linux-s390@vger.kernel.org, "kernel test robot" <lkp@intel.com>,
	"Russell King" <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	x86@kernel.org, "Madhavan Srinivasan" <maddy@linux.ibm.com>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	linuxppc-dev@lists.ozlabs.org, "Paul Walmsley" <pjw@kernel.org>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	"Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"David Laight" <david.laight.linux@gmail.com>,
	"Julia Lawall" <Julia.Lawall@inria.fr>,
	"Nicolas Palix" <nicolas.palix@imag.fr>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Darren Hart" <dvhart@infradead.org>,
	"Davidlohr Bueso" <dave@stgolabs.net>,
	"André Almeida" <andrealmeid@igalia.com>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Christian Brauner" <brauner@kernel.org>,
	"Jan Kara" <jack@suse.cz>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [patch V4 06/12] s390/uaccess: Use unsafe wrappers for ASM GOTO
Date: Wed, 22 Oct 2025 17:00:16 +0200	[thread overview]
Message-ID: <20251022150016.37430Aa6-hca@linux.ibm.com> (raw)
In-Reply-To: <20251022103112.232389777@linutronix.de>

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>