linux-kernel - [patch V2 5/6] x86/futex: Convert to scoped masked user access

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Message-ID: <20250916163252.290994801@linutronix.de>
Date: Tue, 16 Sep 2025 18:33:16 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>,
 x86@...nel.org,
 kernel test robot <lkp@...el.com>,
 Russell King <linux@...linux.org.uk>,
 linux-arm-kernel@...ts.infradead.org,
 Nathan Chancellor <nathan@...nel.org>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 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 V2 5/6] x86/futex: Convert to scoped masked user access

Replace the open coded implementation with the scoped masked user access
mechanism.

No functional change intended.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
---
V2:	Convert to scoped masked access
	Use RW access functions - Christophe
---
 arch/x86/include/asm/futex.h |   76 ++++++++++++++++++-------------------------
 1 file changed, 32 insertions(+), 44 deletions(-)
---
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -48,37 +48,29 @@ do {								\
 static __always_inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 		u32 __user *uaddr)
 {
-	if (can_do_masked_user_access())
-		uaddr = masked_user_access_begin(uaddr);
-	else if (!user_access_begin(uaddr, sizeof(u32)))
-		return -EFAULT;
-
-	switch (op) {
-	case FUTEX_OP_SET:
-		unsafe_atomic_op1("xchgl %0, %2", oval, uaddr, oparg, Efault);
-		break;
-	case FUTEX_OP_ADD:
-		unsafe_atomic_op1(LOCK_PREFIX "xaddl %0, %2", oval,
-				   uaddr, oparg, Efault);
-		break;
-	case FUTEX_OP_OR:
-		unsafe_atomic_op2("orl %4, %3", oval, uaddr, oparg, Efault);
-		break;
-	case FUTEX_OP_ANDN:
-		unsafe_atomic_op2("andl %4, %3", oval, uaddr, ~oparg, Efault);
-		break;
-	case FUTEX_OP_XOR:
-		unsafe_atomic_op2("xorl %4, %3", oval, uaddr, oparg, Efault);
-		break;
-	default:
-		user_access_end();
-		return -ENOSYS;
-	}
-	user_access_end();
+	scoped_masked_user_rw_access(uaddr, return -EFAULT, {
+		switch (op) {
+		case FUTEX_OP_SET:
+			unsafe_atomic_op1("xchgl %0, %2", oval, uaddr, oparg, scope_fault);
+			break;
+		case FUTEX_OP_ADD:
+			unsafe_atomic_op1(LOCK_PREFIX "xaddl %0, %2", oval,
+					  uaddr, oparg, scope_fault);
+			break;
+		case FUTEX_OP_OR:
+			unsafe_atomic_op2("orl %4, %3", oval, uaddr, oparg, scope_fault);
+			break;
+		case FUTEX_OP_ANDN:
+			unsafe_atomic_op2("andl %4, %3", oval, uaddr, ~oparg, scope_fault);
+			break;
+		case FUTEX_OP_XOR:
+			unsafe_atomic_op2("xorl %4, %3", oval, uaddr, oparg, scope_fault);
+			break;
+		default:
+			return -ENOSYS;
+		}
+	});
 	return 0;
-Efault:
-	user_access_end();
-	return -EFAULT;
 }
 
 static inline int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
@@ -86,20 +78,16 @@ static inline int futex_atomic_cmpxchg_i
 {
 	int ret = 0;
 
-	if (can_do_masked_user_access())
-		uaddr = masked_user_access_begin(uaddr);
-	else if (!user_access_begin(uaddr, sizeof(u32)))
-		return -EFAULT;
-	asm volatile("\n"
-		"1:\t" LOCK_PREFIX "cmpxchgl %3, %2\n"
-		"2:\n"
-		_ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, %0) \
-		: "+r" (ret), "=a" (oldval), "+m" (*uaddr)
-		: "r" (newval), "1" (oldval)
-		: "memory"
-	);
-	user_access_end();
-	*uval = oldval;
+	scoped_masked_user_rw_access(uaddr, return -EFAULT, {
+		asm volatile("\n"
+			     "1:\t" LOCK_PREFIX "cmpxchgl %3, %2\n"
+			     "2:\n"
+			     _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG, %0) \
+			     : "+r" (ret), "=a" (oldval), "+m" (*uaddr)
+			     : "r" (newval), "1" (oldval)
+			     : "memory");
+		*uval = oldval;
+	});
 	return ret;
 }