s390/futex: Avoid KMSAN instrumention for user pointers

Similar to commit eb6efdf ("s390/uaccess: add KMSAN support to
put_user() and get_user()") disable KMSAN instrumention for futex inline
assemblies, which contain dereferenced user pointers. With KMSAN
instrumentation this would lead to accesses of shadows for user pointers,
which should not happen.

Handle the futex operations like they copy a value (old) from user
space to kernel space.

Acked-by: Ilya Leoshkevich <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Alexander Gordeev <[email protected]>

Author: hcahca

arch/s390/include/asm/futex.h

@@ -2,18 +2,20 @@
 #ifndef _ASM_S390_FUTEX_H
 #define _ASM_S390_FUTEX_H
 
+#include <linux/instrumented.h>
 #include <linux/uaccess.h>
 #include <linux/futex.h>
 #include <asm/asm-extable.h>
 #include <asm/mmu_context.h>
 #include <asm/errno.h>
 
 #define FUTEX_OP_FUNC(name, insn)						\
-static inline int								\
+static uaccess_kmsan_or_inline int						\
 __futex_atomic_##name(int oparg, int *old, u32 __user *uaddr)			\
 {										\
 	int rc, new;								\
 										\
+	instrument_copy_from_user_before(old, uaddr, sizeof(*old));		\
 	asm_inline volatile(							\
 		"	sacf	256\n"						\
 		"0:	l	%[old],%[uaddr]\n"				\
@@ -30,6 +32,8 @@ __futex_atomic_##name(int oparg, int *old, u32 __user *uaddr)			\
 		  [new] "=&d" (new), [uaddr] "+Q" (*uaddr)			\
 		: [oparg] "d" (oparg)						\
 		: "cc");							\
+	if (!rc)								\
+		instrument_copy_from_user_after(old, uaddr, sizeof(*old), 0);	\
 	return rc;								\
 }
 
@@ -68,11 +72,12 @@ int arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr)
 	return rc;
 }
 
-static inline int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
-						u32 oldval, u32 newval)
+static uaccess_kmsan_or_inline
+int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, u32 oldval, u32 newval)
 {
 	int rc;
 
+	instrument_copy_from_user_before(uval, uaddr, sizeof(*uval));
 	asm_inline volatile(
 		"	sacf	256\n"
 		"0:	cs	%[old],%[new],%[uaddr]\n"
@@ -84,6 +89,7 @@ static inline int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 		: [new] "d" (newval)
 		: "cc", "memory");
 	*uval = oldval;
+	instrument_copy_from_user_after(uval, uaddr, sizeof(*uval), 0);
 	return rc;
 }