[PATCH v4 32/35] s390/uaccess: Add KMSAN support to put_user() and get_user()

Ilya Leoshkevich
2024-06-13T15:40:23Z

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();
--
2.45.1