[PATCH v3 31/34] s390/uaccess: Add KMSAN support to put_user() and get_user()

[Ilya Leoshkevich <iii@linux.ibm.com>]

put_user() uses inline assembly with precise constraints, so Clang is
in principle capable of instrumenting it automatically. Unfortunately,
one of the constraints contains a dereferenced user pointer, and Clang
does not currently distinguish user and kernel pointers. Therefore
KMSAN attempts to access shadow for user pointers, which is not a right
thing to do.

An obvious fix to add __no_sanitize_memory to __put_user_fn() does not
work, since it's __always_inline. And __always_inline cannot be removed
due to the __put_user_bad() trick.

A different obvious fix of using the "a" instead of the "+Q" constraint
degrades the code quality, which is very important here, since it's a
hot path.

Instead, repurpose the __put_user_asm() macro to define
__put_user_{char,short,int,long}_noinstr() functions and mark them with
__no_sanitize_memory. For the non-KMSAN builds make them
__always_inline in order to keep the generated code quality. Also
define __put_user_{char,short,int,long}() functions, which call the
aforementioned ones and which *are* instrumented, because they call
KMSAN hooks, which may be implemented as macros.

The same applies to get_user() as well.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 arch/s390/include/asm/uaccess.h | 111 +++++++++++++++++++++++---------
 1 file changed, 79 insertions(+), 32 deletions(-)

diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index 81ae8a98e7ec..c3c26dd1fc04 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -78,13 +78,24 @@ union oac {
 
 int __noreturn __put_user_bad(void);
 
-#define __put_user_asm(to, from, size)					\
-({									\
+#ifdef CONFIG_KMSAN
+#define GET_PUT_USER_NOINSTR_ATTRIBUTES \
+	noinline __maybe_unused __no_sanitize_memory
+#else
+#define GET_PUT_USER_NOINSTR_ATTRIBUTES __always_inline
+#endif
+
+#define DEFINE_PUT_USER(type)						\
+static GET_PUT_USER_NOINSTR_ATTRIBUTES int				\
+__put_user_##type##_noinstr(unsigned type __user *to,			\
+			    unsigned type *from,			\
+			    unsigned long size)				\
+{									\
 	union oac __oac_spec = {					\
 		.oac1.as = PSW_BITS_AS_SECONDARY,			\
 		.oac1.a = 1,						\
 	};								\
-	int __rc;							\
+	int rc;								\
 									\
 	asm volatile(							\
 		"	lr	0,%[spec]\n"				\
@@ -93,12 +104,28 @@ int __noreturn __put_user_bad(void);
 		"2:\n"							\
 		EX_TABLE_UA_STORE(0b, 2b, %[rc])			\
 		EX_TABLE_UA_STORE(1b, 2b, %[rc])			\
-		: [rc] "=&d" (__rc), [_to] "+Q" (*(to))			\
+		: [rc] "=&d" (rc), [_to] "+Q" (*(to))			\
 		: [_size] "d" (size), [_from] "Q" (*(from)),		\
 		  [spec] "d" (__oac_spec.val)				\
 		: "cc", "0");						\
-	__rc;								\
-})
+	return rc;							\
+}									\
+									\
+static __always_inline int						\
+__put_user_##type(unsigned type __user *to, unsigned type *from,	\
+		  unsigned long size)					\
+{									\
+	int rc;								\
+									\
+	rc = __put_user_##type##_noinstr(to, from, size);		\
+	instrument_put_user(*from, to, size);				\
+	return rc;							\
+}
+
+DEFINE_PUT_USER(char);
+DEFINE_PUT_USER(short);
+DEFINE_PUT_USER(int);
+DEFINE_PUT_USER(long);
 
 static __always_inline int __put_user_fn(void *x, void __user *ptr, unsigned long size)
 {
@@ -106,24 +133,24 @@ static __always_inline int __put_user_fn(void *x, void __user *ptr, unsigned lon
 
 	switch (size) {
 	case 1:
-		rc = __put_user_asm((unsigned char __user *)ptr,
-				    (unsigned char *)x,
-				    size);
+		rc = __put_user_char((unsigned char __user *)ptr,
+				     (unsigned char *)x,
+				     size);
 		break;
 	case 2:
-		rc = __put_user_asm((unsigned short __user *)ptr,
-				    (unsigned short *)x,
-				    size);
+		rc = __put_user_short((unsigned short __user *)ptr,
+				      (unsigned short *)x,
+				      size);
 		break;
 	case 4:
-		rc = __put_user_asm((unsigned int __user *)ptr,
+		rc = __put_user_int((unsigned int __user *)ptr,
 				    (unsigned int *)x,
 				    size);
 		break;
 	case 8:
-		rc = __put_user_asm((unsigned long __user *)ptr,
-				    (unsigned long *)x,
-				    size);
+		rc = __put_user_long((unsigned long __user *)ptr,
+				     (unsigned long *)x,
+				     size);
 		break;
 	default:
 		__put_user_bad();
@@ -134,13 +161,17 @@ static __always_inline int __put_user_fn(void *x, void __user *ptr, unsigned lon
 
 int __noreturn __get_user_bad(void);
 
-#define __get_user_asm(to, from, size)					\
-({									\
+#define DEFINE_GET_USER(type)						\
+static GET_PUT_USER_NOINSTR_ATTRIBUTES int				\
+__get_user_##type##_noinstr(unsigned type *to,				\
+			    unsigned type __user *from,			\
+			    unsigned long size)				\
+{									\
 	union oac __oac_spec = {					\
 		.oac2.as = PSW_BITS_AS_SECONDARY,			\
 		.oac2.a = 1,						\
 	};								\
-	int __rc;							\
+	int rc;								\
 									\
 	asm volatile(							\
 		"	lr	0,%[spec]\n"				\
@@ -149,13 +180,29 @@ int __noreturn __get_user_bad(void);
 		"2:\n"							\
 		EX_TABLE_UA_LOAD_MEM(0b, 2b, %[rc], %[_to], %[_ksize])	\
 		EX_TABLE_UA_LOAD_MEM(1b, 2b, %[rc], %[_to], %[_ksize])	\
-		: [rc] "=&d" (__rc), "=Q" (*(to))			\
+		: [rc] "=&d" (rc), "=Q" (*(to))				\
 		: [_size] "d" (size), [_from] "Q" (*(from)),		\
 		  [spec] "d" (__oac_spec.val), [_to] "a" (to),		\
 		  [_ksize] "K" (size)					\
 		: "cc", "0");						\
-	__rc;								\
-})
+	return rc;							\
+}									\
+									\
+static __always_inline int						\
+__get_user_##type(unsigned type *to, unsigned type __user *from,	\
+		  unsigned long size)					\
+{									\
+	int rc;								\
+									\
+	rc = __get_user_##type##_noinstr(to, from, size);		\
+	instrument_get_user(*to);					\
+	return rc;							\
+}
+
+DEFINE_GET_USER(char);
+DEFINE_GET_USER(short);
+DEFINE_GET_USER(int);
+DEFINE_GET_USER(long);
 
 static __always_inline int __get_user_fn(void *x, const void __user *ptr, unsigned long size)
 {
@@ -163,24 +210,24 @@ static __always_inline int __get_user_fn(void *x, const void __user *ptr, unsign
 
 	switch (size) {
 	case 1:
-		rc = __get_user_asm((unsigned char *)x,
-				    (unsigned char __user *)ptr,
-				    size);
+		rc = __get_user_char((unsigned char *)x,
+				     (unsigned char __user *)ptr,
+				     size);
 		break;
 	case 2:
-		rc = __get_user_asm((unsigned short *)x,
-				    (unsigned short __user *)ptr,
-				    size);
+		rc = __get_user_short((unsigned short *)x,
+				      (unsigned short __user *)ptr,
+				      size);
 		break;
 	case 4:
-		rc = __get_user_asm((unsigned int *)x,
+		rc = __get_user_int((unsigned int *)x,
 				    (unsigned int __user *)ptr,
 				    size);
 		break;
 	case 8:
-		rc = __get_user_asm((unsigned long *)x,
-				    (unsigned long __user *)ptr,
-				    size);
+		rc = __get_user_long((unsigned long *)x,
+				     (unsigned long __user *)ptr,
+				     size);
 		break;
 	default:
 		__get_user_bad();
-- 
2.43.0