asm-generic: uaccess: remove inline strncpy_from_user/strnlen_user

The inline version is used on three NOMMU architectures and is
particularly inefficient when it scans the string one byte at a time
twice. It also lacks a check for user_addr_max(), but this is
probably ok on NOMMU targets.

Consolidate the asm-generic implementation with the library version
that is used everywhere else.  This version is generalized enough to
work efficiently on both MMU and NOMMU targets, and using the
same code everywhere reduces the potential for subtle bugs.

Mark the prototypes as __must_check in the process.

Reviewed-by: Geert Uytterhoeven <[email protected]>
Acked-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

Author: arndb

arch/h8300/Kconfig

@@ -11,6 +11,8 @@ config H8300
 	select GENERIC_IRQ_SHOW
 	select FRAME_POINTER
 	select GENERIC_CPU_DEVICES
+	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 	select MODULES_USE_ELF_RELA
 	select COMMON_CLK
 	select ARCH_WANT_FRAME_POINTERS

arch/m68k/Kconfig

@@ -16,8 +16,8 @@ config M68K
 	select GENERIC_CPU_DEVICES
 	select GENERIC_IOMAP
 	select GENERIC_IRQ_SHOW
-	select GENERIC_STRNCPY_FROM_USER if MMU
-	select GENERIC_STRNLEN_USER if MMU
+	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 	select HAVE_AOUT if MMU
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_DEBUG_BUGVERBOSE

arch/riscv/Kconfig

@@ -56,8 +56,8 @@ config RISCV
 	select GENERIC_PTDUMP if MMU
 	select GENERIC_SCHED_CLOCK
 	select GENERIC_SMP_IDLE_THREAD
-	select GENERIC_STRNCPY_FROM_USER if MMU
-	select GENERIC_STRNLEN_USER if MMU
+	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 	select GENERIC_TIME_VSYSCALL if MMU && 64BIT
 	select HANDLE_DOMAIN_IRQ
 	select HAVE_ARCH_AUDITSYSCALL

include/asm-generic/uaccess.h

@@ -119,6 +119,11 @@ static inline void set_fs(mm_segment_t fs)
 #ifndef uaccess_kernel
 #define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
 #endif
+
+#ifndef user_addr_max
+#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
+#endif
+
 #endif /* CONFIG_SET_FS */
 
 #define access_ok(addr, size) __access_ok((unsigned long)(addr),(size))
@@ -243,44 +248,6 @@ static inline int __get_user_fn(size_t size, const void __user *ptr, void *x)
 
 extern int __get_user_bad(void) __attribute__((noreturn));
 
-/*
- * Copy a null terminated string from userspace.
- */
-#ifndef strncpy_from_user
-static inline long
-strncpy_from_user(char *dst, const char __user *src, long count)
-{
-	char *tmp;
-
-	if (!access_ok(src, 1))
-		return -EFAULT;
-
-	strncpy(dst, (const char __force *)src, count);
-	for (tmp = dst; *tmp && count > 0; tmp++, count--)
-		;
-	return (tmp - dst);
-}
-#endif
-
-#ifndef strnlen_user
-/*
- * Return the size of a string (including the ending 0)
- *
- * Return 0 on exception, a value greater than N if too long
- *
- * Unlike strnlen, strnlen_user includes the nul terminator in
- * its returned count. Callers should check for a returned value
- * greater than N as an indication the string is too long.
- */
-static inline long strnlen_user(const char __user *src, long n)
-{
-	if (!access_ok(src, 1))
-		return 0;
-
-	return strnlen(src, n) + 1;
-}
-#endif
-
 /*
  * Zero Userspace
  */
@@ -305,4 +272,8 @@ clear_user(void __user *to, unsigned long n)
 
 #include <asm/extable.h>
 
+__must_check long strncpy_from_user(char *dst, const char __user *src,
+				    long count);
+__must_check long strnlen_user(const char __user *src, long n);
+
 #endif /* __ASM_GENERIC_UACCESS_H */