xtensa: use generic strncpy_from_user with KASAN

This enables KASAN check of the destination buffer.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/Kconfig

@@ -15,6 +15,7 @@ config XTENSA
 	select GENERIC_IRQ_SHOW
 	select GENERIC_PCI_IOMAP
 	select GENERIC_SCHED_CLOCK
+	select GENERIC_STRNCPY_FROM_USER if KASAN
 	select HAVE_ARCH_KASAN if MMU
 	select HAVE_CC_STACKPROTECTOR
 	select HAVE_DEBUG_KMEMLEAK

arch/xtensa/include/asm/uaccess.h

@@ -44,6 +44,8 @@
 #define __access_ok(addr, size) (__kernel_ok || __user_ok((addr), (size)))
 #define access_ok(type, addr, size) __access_ok((unsigned long)(addr), (size))
 
+#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
+
 /*
  * These are the main single-value transfer routines.  They
  * automatically use the right size if we just have the right pointer
@@ -277,6 +279,8 @@ clear_user(void *addr, unsigned long size)
 #define __clear_user  __xtensa_clear_user
 
 
+#ifndef CONFIG_GENERIC_STRNCPY_FROM_USER
+
 extern long __strncpy_user(char *, const char *, long);
 
 static inline long
@@ -286,6 +290,9 @@ strncpy_from_user(char *dst, const char *src, long count)
 		return __strncpy_user(dst, src, count);
 	return -EFAULT;
 }
+#else
+long strncpy_from_user(char *dst, const char *src, long count);
+#endif
 
 /*
  * Return the size of a string (including the ending 0!)

arch/xtensa/kernel/xtensa_ksyms.c

@@ -44,7 +44,9 @@ EXPORT_SYMBOL(memmove);
 EXPORT_SYMBOL(__memset);
 EXPORT_SYMBOL(__memcpy);
 EXPORT_SYMBOL(__memmove);
+#ifndef CONFIG_GENERIC_STRNCPY_FROM_USER
 EXPORT_SYMBOL(__strncpy_user);
+#endif
 EXPORT_SYMBOL(clear_page);
 EXPORT_SYMBOL(copy_page);