x86: asm: make sure __put_user_size() evaluates pointer once

User access macros must ensure their arguments are evaluated only once if
they are used more than once in the macro body.  Adding
instrument_put_user() to __put_user_size() resulted in double evaluation
of the `ptr` argument, which led to correctness issues when performing
e.g.  unsafe_put_user(..., p++, ...).

To fix those issues, evaluate the `ptr` argument of __put_user_size() at
the beginning of the macro.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 888f84a ("x86: asm: instrument usercopy in get_user() and put_user()")
Signed-off-by: Alexander Potapenko <[email protected]>
Reported-by: youling257 <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ramosian-glider

arch/x86/include/asm/uaccess.h

@@ -254,24 +254,25 @@ extern void __put_user_nocheck_8(void);
 #define __put_user_size(x, ptr, size, label)				\
 do {									\
 	__typeof__(*(ptr)) __x = (x); /* eval x once */			\
-	__chk_user_ptr(ptr);						\
+	__typeof__(ptr) __ptr = (ptr); /* eval ptr once */		\
+	__chk_user_ptr(__ptr);						\
 	switch (size) {							\
 	case 1:								\
-		__put_user_goto(__x, ptr, "b", "iq", label);		\
+		__put_user_goto(__x, __ptr, "b", "iq", label);		\
 		break;							\
 	case 2:								\
-		__put_user_goto(__x, ptr, "w", "ir", label);		\
+		__put_user_goto(__x, __ptr, "w", "ir", label);		\
 		break;							\
 	case 4:								\
-		__put_user_goto(__x, ptr, "l", "ir", label);		\
+		__put_user_goto(__x, __ptr, "l", "ir", label);		\
 		break;							\
 	case 8:								\
-		__put_user_goto_u64(__x, ptr, label);			\
+		__put_user_goto_u64(__x, __ptr, label);			\
 		break;							\
 	default:							\
 		__put_user_bad();					\
 	}								\
-	instrument_put_user(__x, ptr, size);				\
+	instrument_put_user(__x, __ptr, size);				\
 } while (0)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT