linux-kernel - [patch V3 03/12] x86/uaccess: Use unsafe wrappers for ASM GOTO

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Message-ID: <20251017093030.001666876@linutronix.de>
Date: Fri, 17 Oct 2025 12:09:00 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.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>,
 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,
 Heiko Carstens <hca@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>,
 linux-s390@...r.kernel.org,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Andrew Cooper <andrew.cooper3@...rix.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: [patch V3 03/12] x86/uaccess: Use unsafe wrappers for ASM GOTO

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.

Rename unsafe_*_user() to arch_unsafe_*_user() which makes the generic
uaccess header wrap it with a local label that makes both compilers emit
correct code. Same for the kernel_nofault() variants.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
---
 arch/x86/include/asm/uaccess.h |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -528,18 +528,18 @@ static __must_check __always_inline bool
 #define user_access_save()	smap_save()
 #define user_access_restore(x)	smap_restore(x)
 
-#define unsafe_put_user(x, ptr, label)	\
+#define arch_unsafe_put_user(x, ptr, label)	\
 	__put_user_size((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)), label)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-#define unsafe_get_user(x, ptr, err_label)					\
+#define arch_unsafe_get_user(x, ptr, err_label)					\
 do {										\
 	__inttype(*(ptr)) __gu_val;						\
 	__get_user_size(__gu_val, (ptr), sizeof(*(ptr)), err_label);		\
 	(x) = (__force __typeof__(*(ptr)))__gu_val;				\
 } while (0)
 #else // !CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-#define unsafe_get_user(x, ptr, err_label)					\
+#define arch_unsafe_get_user(x, ptr, err_label)					\
 do {										\
 	int __gu_err;								\
 	__inttype(*(ptr)) __gu_val;						\
@@ -618,11 +618,11 @@ do {									\
 } while (0)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-#define __get_kernel_nofault(dst, src, type, err_label)			\
+#define arch_get_kernel_nofault(dst, src, type, err_label)		\
 	__get_user_size(*((type *)(dst)), (__force type __user *)(src),	\
 			sizeof(type), err_label)
 #else // !CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-#define __get_kernel_nofault(dst, src, type, err_label)			\
+#define arch_get_kernel_nofault(dst, src, type, err_label)			\
 do {									\
 	int __kr_err;							\
 									\
@@ -633,7 +633,7 @@ do {									\
 } while (0)
 #endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT
 
-#define __put_kernel_nofault(dst, src, type, err_label)			\
+#define arch_put_kernel_nofault(dst, src, type, err_label)		\
 	__put_user_size(*((type *)(src)), (__force type __user *)(dst),	\
 			sizeof(type), err_label)