[RFC][PATCH 5/7] x86: convert arch_futex_atomic_op_inuser() to user_access_begin/user_access_end()

Al Viro
2020-03-23T18:51:31Z

From: Al Viro <viro@zeniv.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@zeniv.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