linux-kernel - [RFC][PATCH 5/7] x86: convert arch_futex_atomic_op_inuser() to user_access_begin/user_access

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Date:   Mon, 23 Mar 2020 18:51:25 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: [RFC][PATCH 5/7] x86: convert arch_futex_atomic_op_inuser() to user_access_begin/user_access_end()

From: Al Viro <viro@...iv.linux.org.uk>

Lift stac/clac pairs from __futex_atomic_op{1,2} into arch_futex_atomic_op_inuser(),
fold them with access_ok() in there.  The switch in arch_futex_atomic_op_inuser()
is what has required the previous (objtool) commit...

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 arch/x86/include/asm/futex.h | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/futex.h b/arch/x86/include/asm/futex.h
index 6bcd1c1486d9..cf6e57fb5b22 100644
--- a/arch/x86/include/asm/futex.h
+++ b/arch/x86/include/asm/futex.h
@@ -13,9 +13,8 @@
 #include <asm/smap.h>
 
 #define __futex_atomic_op1(insn, ret, oldval, uaddr, oparg)	\
-	asm volatile("\t" ASM_STAC "\n"				\
-		     "1:\t" insn "\n"				\
-		     "2:\t" ASM_CLAC "\n"			\
+	asm volatile("1:\t" insn "\n"				\
+		     "2:\n"					\
 		     "\t.section .fixup,\"ax\"\n"		\
 		     "3:\tmov\t%3, %1\n"			\
 		     "\tjmp\t2b\n"				\
@@ -25,13 +24,12 @@
 		     : "i" (-EFAULT), "0" (oparg), "1" (0))
 
 #define __futex_atomic_op2(insn, ret, oldval, uaddr, oparg)	\
-	asm volatile("\t" ASM_STAC "\n"				\
-		     "1:\tmovl	%2, %0\n"			\
+	asm volatile("1:\tmovl	%2, %0\n"			\
 		     "\tmovl\t%0, %3\n"				\
 		     "\t" insn "\n"				\
 		     "2:\t" LOCK_PREFIX "cmpxchgl %3, %2\n"	\
 		     "\tjnz\t1b\n"				\
-		     "3:\t" ASM_CLAC "\n"			\
+		     "3:\n"					\
 		     "\t.section .fixup,\"ax\"\n"		\
 		     "4:\tmov\t%5, %1\n"			\
 		     "\tjmp\t3b\n"				\
@@ -42,12 +40,12 @@
 		       "+m" (*uaddr), "=&r" (tem)		\
 		     : "r" (oparg), "i" (-EFAULT), "1" (0))
 
-static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
+static __always_inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 		u32 __user *uaddr)
 {
 	int oldval = 0, ret, tem;
 
-	if (!access_ok(uaddr, sizeof(u32)))
+	if (!user_access_begin(uaddr, sizeof(u32)))
 		return -EFAULT;
 
 	switch (op) {
@@ -70,6 +68,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 	default:
 		ret = -ENOSYS;
 	}
+	user_access_end();
 
 	if (!ret)
 		*oval = oldval;
-- 
2.11.0