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

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Message-ID: <20251022150016.37430Aa6-hca@linux.ibm.com>
Date: Wed, 22 Oct 2025 17:00:16 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kernel test robot <lkp@...el.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linuxppc-dev@...ts.ozlabs.org, Paul Walmsley <pjw@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>, linux-riscv@...ts.infradead.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        David Laight <david.laight.linux@...il.com>,
        Julia Lawall <Julia.Lawall@...ia.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        André Almeida <andrealmeid@...lia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [patch V4 06/12] s390/uaccess: Use unsafe wrappers for ASM GOTO

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@...utronix.de>
> Cc: Heiko Carstens <hca@...ux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
> Cc: Sven Schnelle <svens@...ux.ibm.com>
> Cc: linux-s390@...r.kernel.org
> ---
>  arch/s390/include/asm/uaccess.h |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

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