Merge branch 'generic-string-functions'

This makes <asm/word-at-a-time.h> actually live up to its promise of
allowing architectures to help tune the string functions that do their
work a word at a time.

David had already taken the x86 strncpy_from_user() function, modified
it to work on sparc, and then done the extra work to make it generically
useful. This then expands on that work by making x86 use that generic
version, completing the circle.

But more importantly, it fixes up the word-at-a-time interfaces so that
it's now easy to also support things like strnlen_user(), and pretty
much most random string functions.

David reports that it all works fine on sparc, and Jonas Bonn reported
that an earlier version of this worked on OpenRISC too. It's pretty
easy for architectures to add support for this and just replace their
private versions with the generic code.

* generic-string-functions:
sparc: use the new generic strnlen_user() function
x86: use the new generic strnlen_user() function
lib: add generic strnlen_user() function
word-at-a-time: make the interfaces truly generic
x86: use generic strncpy_from_user routine

arch/openrisc/include/asm/Kbuild

···
 generic-y += types.h
 generic-y += ucontext.h
 generic-y += user.h
+generic-y += word-at-a-time.h

arch/sparc/Kconfig

···
 	select GENERIC_CMOS_UPDATE
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 
 config SPARC32
 	def_bool !64BIT

arch/sparc/include/asm/Kbuild

···
 generic-y += local64.h
 generic-y += irq_regs.h
 generic-y += local.h
+generic-y += word-at-a-time.h

arch/sparc/include/asm/uaccess_32.h

···
 
 #ifndef __ASSEMBLY__
 
+#include <asm/processor.h>
+
 #define ARCH_HAS_SORT_EXTABLE
 #define ARCH_HAS_SEARCH_EXTABLE
 
···
 		return n;
 }
 
-extern long __strlen_user(const char __user *);
-extern long __strnlen_user(const char __user *, long len);
-
-static inline long strlen_user(const char __user *str)
-{
-	if (!access_ok(VERIFY_READ, str, 0))
-		return 0;
-	else
-		return __strlen_user(str);
-}
-
-static inline long strnlen_user(const char __user *str, long len)
-{
-	if (!access_ok(VERIFY_READ, str, 0))
-		return 0;
-	else
-		return __strnlen_user(str, len);
-}
+extern __must_check long strlen_user(const char __user *str);
+extern __must_check long strnlen_user(const char __user *str, long n);
 
 #endif  /* __ASSEMBLY__ */
 

arch/sparc/include/asm/uaccess_64.h

···
 
 #ifndef __ASSEMBLY__
 
+#include <asm/processor.h>
+
 /*
  * Sparc64 is segmented, though more like the M68K than the I386.
  * We use the secondary ASI to address user memory, which references a
···
 
 #define clear_user __clear_user
 
-extern long __strlen_user(const char __user *);
-extern long __strnlen_user(const char __user *, long len);
+extern __must_check long strlen_user(const char __user *str);
+extern __must_check long strnlen_user(const char __user *str, long n);
 
-#define strlen_user __strlen_user
-#define strnlen_user __strnlen_user
 #define __copy_to_user_inatomic ___copy_to_user
 #define __copy_from_user_inatomic ___copy_from_user
 

arch/sparc/lib/Makefile

···
 lib-y                 += checksum_$(BITS).o
 lib-$(CONFIG_SPARC32) += blockops.o
 lib-y                 += memscan_$(BITS).o memcmp.o strncmp_$(BITS).o
-lib-y                 += strlen_user_$(BITS).o
 lib-$(CONFIG_SPARC32) += divdi3.o udivdi3.o
 lib-$(CONFIG_SPARC32) += copy_user.o locks.o
 lib-$(CONFIG_SPARC64) += atomic_64.o

arch/sparc/lib/ksyms.c

···
 
 /* string functions */
 EXPORT_SYMBOL(strlen);
-EXPORT_SYMBOL(__strlen_user);
-EXPORT_SYMBOL(__strnlen_user);
 EXPORT_SYMBOL(strncmp);
 
 /* mem* functions */

arch/sparc/lib/strlen_user_32.S

···
-/* strlen_user.S: Sparc optimized strlen_user code
- *
- * Return length of string in userspace including terminating 0
- * or 0 for error
- *
- * Copyright (C) 1991,1996 Free Software Foundation
- * Copyright (C) 1996 David S. Miller ([e-mail])
- * Copyright (C) 1996 Jakub Jelinek ([e-mail])
- */
-
-#define LO_MAGIC 0x01010101
-#define HI_MAGIC 0x80808080
-
-10:
-	ldub	[%o0], %o5
-	cmp	%o5, 0
-	be	1f
-	 add	%o0, 1, %o0
-	andcc	%o0, 3, %g0
-	be	4f
-	 or	%o4, %lo(HI_MAGIC), %o3
-11:
-	ldub	[%o0], %o5
-	cmp	%o5, 0
-	be	2f
-	 add	%o0, 1, %o0
-	andcc	%o0, 3, %g0
-	be	5f
-	 sethi	%hi(LO_MAGIC), %o4
-12:
-	ldub	[%o0], %o5
-	cmp	%o5, 0
-	be	3f
-	 add	%o0, 1, %o0
-	b	13f
-	 or	%o4, %lo(LO_MAGIC), %o2
-1:
-	retl
-	 mov	1, %o0
-2:
-	retl
-	 mov	2, %o0
-3:
-	retl
-	 mov	3, %o0
-
-	.align 4
-	.global __strlen_user, __strnlen_user
-__strlen_user:
-	sethi	%hi(32768), %o1
-__strnlen_user:
-	mov	%o1, %g1
-	mov	%o0, %o1
-	andcc	%o0, 3, %g0
-	bne	10b
-	 sethi	%hi(HI_MAGIC), %o4
-	or	%o4, %lo(HI_MAGIC), %o3
-4:
-	sethi	%hi(LO_MAGIC), %o4
-5:
-	or	%o4, %lo(LO_MAGIC), %o2
-13:
-	ld	[%o0], %o5
-2:
-	sub	%o5, %o2, %o4
-	andcc	%o4, %o3, %g0
-	bne	82f
-	 add	%o0, 4, %o0
-	sub	%o0, %o1, %g2
-81:	cmp	%g2, %g1
-	blu	13b
-	 mov	%o0, %o4
-	ba,a	1f
-
-	/* Check every byte. */
-82:	srl	%o5, 24, %g5
-	andcc	%g5, 0xff, %g0
-	be	1f
-	 add	%o0, -3, %o4
-	srl	%o5, 16, %g5
-	andcc	%g5, 0xff, %g0
-	be	1f
-	 add	%o4, 1, %o4
-	srl	%o5, 8, %g5
-	andcc	%g5, 0xff, %g0
-	be	1f
-	 add	%o4, 1, %o4
-	andcc	%o5, 0xff, %g0
-	bne	81b
-	 sub	%o0, %o1, %g2
-
-	add	%o4, 1, %o4
-1:
-	retl
-	 sub	%o4, %o1, %o0
-
-	.section .fixup,#alloc,#execinstr
-	.align	4
-9:
-	retl
-	 clr	%o0
-
-	.section __ex_table,#alloc
-	.align	4
-
-	.word	10b, 9b
-	.word	11b, 9b
-	.word	12b, 9b
-	.word	13b, 9b

arch/sparc/lib/strlen_user_64.S

···
-/* strlen_user.S: Sparc64 optimized strlen_user code
- *
- * Return length of string in userspace including terminating 0
- * or 0 for error
- *
- * Copyright (C) 1991,1996 Free Software Foundation
- * Copyright (C) 1996,1999 David S. Miller ([e-mail])
- * Copyright (C) 1996,1997 Jakub Jelinek ([e-mail])
- */
-
-#include <linux/linkage.h>
-#include <asm/asi.h>
-
-#define LO_MAGIC 0x01010101
-#define HI_MAGIC 0x80808080
-
-	.align 4
-ENTRY(__strlen_user)
-	sethi	%hi(32768), %o1
-ENTRY(__strnlen_user)
-	mov	%o1, %g1
-	mov	%o0, %o1
-	andcc	%o0, 3, %g0
-	be,pt	%icc, 9f
-	 sethi	%hi(HI_MAGIC), %o4
-10:	lduba	[%o0] %asi, %o5
-	brz,pn	%o5, 21f
-	 add	%o0, 1, %o0
-	andcc	%o0, 3, %g0
-	be,pn	%icc, 4f
-	 or	%o4, %lo(HI_MAGIC), %o3
-11:	lduba	[%o0] %asi, %o5
-	brz,pn	%o5, 22f
-	 add	%o0, 1, %o0
-	andcc	%o0, 3, %g0
-	be,pt	%icc, 13f
-	 srl	%o3, 7, %o2
-12:	lduba	[%o0] %asi, %o5
-	brz,pn	%o5, 23f
-	 add	%o0, 1, %o0
-	ba,pt	%icc, 2f
-15:	 lda	[%o0] %asi, %o5
-9:	or	%o4, %lo(HI_MAGIC), %o3
-4:	srl	%o3, 7, %o2
-13:	lda	[%o0] %asi, %o5
-2:	sub	%o5, %o2, %o4
-	andcc	%o4, %o3, %g0
-	bne,pn	%icc, 82f
-	 add	%o0, 4, %o0
-	sub	%o0, %o1, %g2
-81:	cmp	%g2, %g1
-	blu,pt	%icc, 13b
-	 mov	%o0, %o4
-	ba,a,pt	%xcc, 1f
-
-	/* Check every byte. */
-82:	srl	%o5, 24, %g7
-	andcc	%g7, 0xff, %g0
-	be,pn	%icc, 1f
-	 add	%o0, -3, %o4
-	srl	%o5, 16, %g7
-	andcc	%g7, 0xff, %g0
-	be,pn	%icc, 1f
-	 add	%o4, 1, %o4
-	srl	%o5, 8, %g7
-	andcc	%g7, 0xff, %g0
-	be,pn	%icc, 1f
-	 add	%o4, 1, %o4
-	andcc	%o5, 0xff, %g0
-	bne,pt	%icc, 81b
-	 sub	%o0, %o1, %g2
-	add	%o4, 1, %o4
-1:	retl
-	 sub	%o4, %o1, %o0
-21:	retl
-	 mov	1, %o0
-22:	retl
-	 mov	2, %o0
-23:	retl
-	 mov	3, %o0
-ENDPROC(__strlen_user)
-ENDPROC(__strnlen_user)
-
-        .section .fixup,#alloc,#execinstr
-        .align  4
-30:
-        retl
-         clr    %o0
-
-	.section __ex_table,"a"
-	.align	4
-
-	.word	10b, 30b
-	.word	11b, 30b
-	.word	12b, 30b
-	.word	15b, 30b
-	.word	13b, 30b

arch/x86/Kconfig

···
 	select GENERIC_CLOCKEVENTS_BROADCAST if X86_64 || (X86_32 && X86_LOCAL_APIC)
 	select GENERIC_TIME_VSYSCALL if X86_64
 	select KTIME_SCALAR if X86_32
+	select GENERIC_STRNCPY_FROM_USER
+	select GENERIC_STRNLEN_USER
 
 config INSTRUCTION_DECODER
 	def_bool (KPROBES || PERF_EVENTS || UPROBES)

arch/x86/include/asm/uaccess.h

···
 
 #define segment_eq(a, b)	((a).seg == (b).seg)
 
+#define user_addr_max() (current_thread_info()->addr_limit.seg)
 #define __addr_ok(addr)					\
 	((unsigned long __force)(addr) <		\
 	 (current_thread_info()->addr_limit.seg))
···
 copy_from_user_nmi(void *to, const void __user *from, unsigned long n);
 extern __must_check long
 strncpy_from_user(char *dst, const char __user *src, long count);
+
+extern __must_check long strlen_user(const char __user *str);
+extern __must_check long strnlen_user(const char __user *str, long n);
 
 /*
  * movsl can be slow when source and dest are not both 8-byte aligned

arch/x86/include/asm/uaccess_32.h

···
 	return n;
 }
 
-/**
- * strlen_user: - Get the size of a string in user space.
- * @str: The string to measure.
- *
- * Context: User context only.  This function may sleep.
- *
- * Get the size of a NUL-terminated string in user space.
- *
- * Returns the size of the string INCLUDING the terminating NUL.
- * On exception, returns 0.
- *
- * If there is a limit on the length of a valid string, you may wish to
- * consider using strnlen_user() instead.
- */
-#define strlen_user(str) strnlen_user(str, LONG_MAX)
-
-long strnlen_user(const char __user *str, long n);
 unsigned long __must_check clear_user(void __user *mem, unsigned long len);
 unsigned long __must_check __clear_user(void __user *mem, unsigned long len);
 

arch/x86/include/asm/uaccess_64.h

···
 	}
 }
 
-__must_check long strnlen_user(const char __user *str, long n);
-__must_check long __strnlen_user(const char __user *str, long n);
-__must_check long strlen_user(const char __user *str);
 __must_check unsigned long clear_user(void __user *mem, unsigned long len);
 __must_check unsigned long __clear_user(void __user *mem, unsigned long len);
 

arch/x86/include/asm/word-at-a-time.h

···
  * bit count instruction, that might be better than the multiply
  * and shift, for example.
  */
+struct word_at_a_time {
+	const unsigned long one_bits, high_bits;
+};
+
+#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }
 
 #ifdef CONFIG_64BIT
 
···
 
 #endif
 
-/* Return the high bit set in the first byte that is a zero */
-static inline unsigned long has_zero(unsigned long a)
+/* Return nonzero if it has a zero */
+static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)
 {
-	return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
+	unsigned long mask = ((a - c->one_bits) & ~a) & c->high_bits;
+	*bits = mask;
+	return mask;
+}
+
+static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c)
+{
+	return bits;
+}
+
+static inline unsigned long create_zero_mask(unsigned long bits)
+{
+	bits = (bits - 1) & ~bits;
+	return bits >> 7;
+}
+
+/* The mask we created is directly usable as a bytemask */
+#define zero_bytemask(mask) (mask)
+
+static inline unsigned long find_zero(unsigned long mask)
+{
+	return count_masked_bytes(mask);
 }
 
 /*

arch/x86/lib/usercopy.c

···
 	return len;
 }
 EXPORT_SYMBOL_GPL(copy_from_user_nmi);
-
-/*
- * Do a strncpy, return length of string without final '\0'.
- * 'count' is the user-supplied count (return 'count' if we
- * hit it), 'max' is the address space maximum (and we return
- * -EFAULT if we hit it).
- */
-static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
-{
-	long res = 0;
-
-	/*
-	 * Truncate 'max' to the user-specified limit, so that
-	 * we only have one limit we need to check in the loop
-	 */
-	if (max > count)
-		max = count;
-
-	while (max >= sizeof(unsigned long)) {
-		unsigned long c, mask;
-
-		/* Fall back to byte-at-a-time if we get a page fault */
-		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
-			break;
-		mask = has_zero(c);
-		if (mask) {
-			mask = (mask - 1) & ~mask;
-			mask >>= 7;
-			*(unsigned long *)(dst+res) = c & mask;
-			return res + count_masked_bytes(mask);
-		}
-		*(unsigned long *)(dst+res) = c;
-		res += sizeof(unsigned long);
-		max -= sizeof(unsigned long);
-	}
-
-	while (max) {
-		char c;
-
-		if (unlikely(__get_user(c,src+res)))
-			return -EFAULT;
-		dst[res] = c;
-		if (!c)
-			return res;
-		res++;
-		max--;
-	}
-
-	/*
-	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
-	 * too? If so, that's ok - we got as much as the user asked for.
-	 */
-	if (res >= count)
-		return res;
-
-	/*
-	 * Nope: we hit the address space limit, and we still had more
-	 * characters the caller would have wanted. That's an EFAULT.
-	 */
-	return -EFAULT;
-}
-
-/**
- * strncpy_from_user: - Copy a NUL terminated string from userspace.
- * @dst:   Destination address, in kernel space.  This buffer must be at
- *         least @count bytes long.
- * @src:   Source address, in user space.
- * @count: Maximum number of bytes to copy, including the trailing NUL.
- *
- * Copies a NUL-terminated string from userspace to kernel space.
- *
- * On success, returns the length of the string (not including the trailing
- * NUL).
- *
- * If access to userspace fails, returns -EFAULT (some data may have been
- * copied).
- *
- * If @count is smaller than the length of the string, copies @count bytes
- * and returns @count.
- */
-long
-strncpy_from_user(char *dst, const char __user *src, long count)
-{
-	unsigned long max_addr, src_addr;
-
-	if (unlikely(count <= 0))
-		return 0;
-
-	max_addr = current_thread_info()->addr_limit.seg;
-	src_addr = (unsigned long)src;
-	if (likely(src_addr < max_addr)) {
-		unsigned long max = max_addr - src_addr;
-		return do_strncpy_from_user(dst, src, count, max);
-	}
-	return -EFAULT;
-}
-EXPORT_SYMBOL(strncpy_from_user);

arch/x86/lib/usercopy_32.c

···
 }
 EXPORT_SYMBOL(__clear_user);
 
-/**
- * strnlen_user: - Get the size of a string in user space.
- * @s: The string to measure.
- * @n: The maximum valid length
- *
- * Get the size of a NUL-terminated string in user space.
- *
- * Returns the size of the string INCLUDING the terminating NUL.
- * On exception, returns 0.
- * If the string is too long, returns a value greater than @n.
- */
-long strnlen_user(const char __user *s, long n)
-{
-	unsigned long mask = -__addr_ok(s);
-	unsigned long res, tmp;
-
-	might_fault();
-
-	__asm__ __volatile__(
-		"	testl %0, %0\n"
-		"	jz 3f\n"
-		"	andl %0,%%ecx\n"
-		"0:	repne; scasb\n"
-		"	setne %%al\n"
-		"	subl %%ecx,%0\n"
-		"	addl %0,%%eax\n"
-		"1:\n"
-		".section .fixup,\"ax\"\n"
-		"2:	xorl %%eax,%%eax\n"
-		"	jmp 1b\n"
-		"3:	movb $1,%%al\n"
-		"	jmp 1b\n"
-		".previous\n"
-		_ASM_EXTABLE(0b,2b)
-		:"=&r" (n), "=&D" (s), "=&a" (res), "=&c" (tmp)
-		:"0" (n), "1" (s), "2" (0), "3" (mask)
-		:"cc");
-	return res & mask;
-}
-EXPORT_SYMBOL(strnlen_user);
-
 #ifdef CONFIG_X86_INTEL_USERCOPY
 static unsigned long
 __copy_user_intel(void __user *to, const void *from, unsigned long size)

arch/x86/lib/usercopy_64.c

···
 }
 EXPORT_SYMBOL(clear_user);
 
-/*
- * Return the size of a string (including the ending 0)
- *
- * Return 0 on exception, a value greater than N if too long
- */
-
-long __strnlen_user(const char __user *s, long n)
-{
-	long res = 0;
-	char c;
-
-	while (1) {
-		if (res>n)
-			return n+1;
-		if (__get_user(c, s))
-			return 0;
-		if (!c)
-			return res+1;
-		res++;
-		s++;
-	}
-}
-EXPORT_SYMBOL(__strnlen_user);
-
-long strnlen_user(const char __user *s, long n)
-{
-	if (!access_ok(VERIFY_READ, s, 1))
-		return 0;
-	return __strnlen_user(s, n);
-}
-EXPORT_SYMBOL(strnlen_user);
-
-long strlen_user(const char __user *s)
-{
-	long res = 0;
-	char c;
-
-	for (;;) {
-		if (get_user(c, s))
-			return 0;
-		if (!c)
-			return res+1;
-		res++;
-		s++;
-	}
-}
-EXPORT_SYMBOL(strlen_user);
-
 unsigned long copy_in_user(void __user *to, const void __user *from, unsigned len)
 {
 	if (access_ok(VERIFY_WRITE, to, len) && access_ok(VERIFY_READ, from, len)) { 

fs/namei.c

···
  */
 static inline unsigned long hash_name(const char *name, unsigned int *hashp)
 {
-	unsigned long a, mask, hash, len;
+	unsigned long a, b, adata, bdata, mask, hash, len;
+	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
 
 	hash = a = 0;
 	len = -sizeof(unsigned long);
···
 		hash = (hash + a) * 9;
 		len += sizeof(unsigned long);
 		a = load_unaligned_zeropad(name+len);
-		/* Do we have any NUL or '/' bytes in this word? */
-		mask = has_zero(a) | has_zero(a ^ REPEAT_BYTE('/'));
-	} while (!mask);
+		b = a ^ REPEAT_BYTE('/');
+	} while (!(has_zero(a, &adata, &constants) | has_zero(b, &bdata, &constants)));
 
-	/* The mask *below* the first high bit set */
-	mask = (mask - 1) & ~mask;
-	mask >>= 7;
-	hash += a & mask;
+	adata = prep_zero_mask(a, adata, &constants);
+	bdata = prep_zero_mask(b, bdata, &constants);
+
+	mask = create_zero_mask(adata | bdata);
+
+	hash += a & zero_bytemask(mask);
 	*hashp = fold_hash(hash);
 
-	return len + count_masked_bytes(mask);
+	return len + find_zero(mask);
 }
 
 #else

include/asm-generic/word-at-a-time.h

···
+#ifndef _ASM_WORD_AT_A_TIME_H
+#define _ASM_WORD_AT_A_TIME_H
+
+/*
+ * This says "generic", but it's actually big-endian only.
+ * Little-endian can use more efficient versions of these
+ * interfaces, see for example
+ *	 arch/x86/include/asm/word-at-a-time.h
+ * for those.
+ */
+
+#include <linux/kernel.h>
+
+struct word_at_a_time {
+	const unsigned long high_bits, low_bits;
+};
+
+#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0xfe) + 1, REPEAT_BYTE(0x7f) }
+
+/* Bit set in the bytes that have a zero */
+static inline long prep_zero_mask(unsigned long val, unsigned long rhs, const struct word_at_a_time *c)
+{
+	unsigned long mask = (val & c->low_bits) + c->low_bits;
+	return ~(mask | rhs);
+}
+
+#define create_zero_mask(mask) (mask)
+
+static inline long find_zero(unsigned long mask)
+{
+	long byte = 0;
+#ifdef CONFIG_64BIT
+	if (mask >> 32)
+		mask >>= 32;
+	else
+		byte = 4;
+#endif
+	if (mask >> 16)
+		mask >>= 16;
+	else
+		byte += 2;
+	return (mask >> 8) ? byte : byte + 1;
+}
+
+static inline bool has_zero(unsigned long val, unsigned long *data, const struct word_at_a_time *c)
+{
+	unsigned long rhs = val | c->low_bits;
+	*data = rhs;
+	return (val + c->high_bits) & ~rhs;
+}
+
+#endif /* _ASM_WORD_AT_A_TIME_H */

lib/Kconfig

···
 config GENERIC_STRNCPY_FROM_USER
 	bool
 
+config GENERIC_STRNLEN_USER
+	bool
+
 config GENERIC_FIND_FIRST_BIT
 	bool
 

lib/Makefile

···
 obj-$(CONFIG_DDR) += jedec_ddr_data.o
 
 obj-$(CONFIG_GENERIC_STRNCPY_FROM_USER) += strncpy_from_user.o
+obj-$(CONFIG_GENERIC_STRNLEN_USER) += strnlen_user.o
 
 obj-$(CONFIG_STMP_DEVICE) += stmp_device.o
 

lib/strncpy_from_user.c

···
 #include <linux/errno.h>
 
 #include <asm/byteorder.h>
-
-static inline long find_zero(unsigned long mask)
-{
-	long byte = 0;
-
-#ifdef __BIG_ENDIAN
-#ifdef CONFIG_64BIT
-	if (mask >> 32)
-		mask >>= 32;
-	else
-		byte = 4;
-#endif
-	if (mask >> 16)
-		mask >>= 16;
-	else
-		byte += 2;
-	return (mask >> 8) ? byte : byte + 1;
-#else
-#ifdef CONFIG_64BIT
-	if (!((unsigned int) mask)) {
-		mask >>= 32;
-		byte = 4;
-	}
-#endif
-	if (!(mask & 0xffff)) {
-		mask >>= 16;
-		byte += 2;
-	}
-	return (mask & 0xff) ? byte : byte + 1;
-#endif
-}
+#include <asm/word-at-a-time.h>
 
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 #define IS_UNALIGNED(src, dst)	0
···
  */
 static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
 {
-	const unsigned long high_bits = REPEAT_BYTE(0xfe) + 1;
-	const unsigned long low_bits = REPEAT_BYTE(0x7f);
+	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
 	long res = 0;
 
 	/*
···
 		goto byte_at_a_time;
 
 	while (max >= sizeof(unsigned long)) {
-		unsigned long c, v, rhs;
+		unsigned long c, data;
 
 		/* Fall back to byte-at-a-time if we get a page fault */
 		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
 			break;
-		rhs = c | low_bits;
-		v = (c + high_bits) & ~rhs;
 		*(unsigned long *)(dst+res) = c;
-		if (v) {
-			v = (c & low_bits) + low_bits;
-			v = ~(v | rhs);
-			return res + find_zero(v);
+		if (has_zero(c, &data, &constants)) {
+			data = prep_zero_mask(c, data, &constants);
+			data = create_zero_mask(data);
+			return res + find_zero(data);
 		}
 		res += sizeof(unsigned long);
 		max -= sizeof(unsigned long);

lib/strnlen_user.c

···
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/uaccess.h>
+
+#include <asm/word-at-a-time.h>
+
+/* Set bits in the first 'n' bytes when loaded from memory */
+#ifdef __LITTLE_ENDIAN
+#  define aligned_byte_mask(n) ((1ul << 8*(n))-1)
+#else
+#  define aligned_byte_mask(n) (~0xfful << 8*(7-(n)))
+#endif
+
+/*
+ * Do a strnlen, return length of string *with* final '\0'.
+ * 'count' is the user-supplied count, while 'max' is the
+ * address space maximum.
+ *
+ * Return 0 for exceptions (which includes hitting the address
+ * space maximum), or 'count+1' if hitting the user-supplied
+ * maximum count.
+ *
+ * NOTE! We can sometimes overshoot the user-supplied maximum
+ * if it fits in a aligned 'long'. The caller needs to check
+ * the return value against "> max".
+ */
+static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max)
+{
+	const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
+	long align, res = 0;
+	unsigned long c;
+
+	/*
+	 * Truncate 'max' to the user-specified limit, so that
+	 * we only have one limit we need to check in the loop
+	 */
+	if (max > count)
+		max = count;
+
+	/*
+	 * Do everything aligned. But that means that we
+	 * need to also expand the maximum..
+	 */
+	align = (sizeof(long) - 1) & (unsigned long)src;
+	src -= align;
+	max += align;
+
+	if (unlikely(__get_user(c,(unsigned long __user *)src)))
+		return 0;
+	c |= aligned_byte_mask(align);
+
+	for (;;) {
+		unsigned long data;
+		if (has_zero(c, &data, &constants)) {
+			data = prep_zero_mask(c, data, &constants);
+			data = create_zero_mask(data);
+			return res + find_zero(data) + 1 - align;
+		}
+		res += sizeof(unsigned long);
+		if (unlikely(max < sizeof(unsigned long)))
+			break;
+		max -= sizeof(unsigned long);
+		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))
+			return 0;
+	}
+	res -= align;
+
+	/*
+	 * Uhhuh. We hit 'max'. But was that the user-specified maximum
+	 * too? If so, return the marker for "too long".
+	 */
+	if (res >= count)
+		return count+1;
+
+	/*
+	 * Nope: we hit the address space limit, and we still had more
+	 * characters the caller would have wanted. That's 0.
+	 */
+	return 0;
+}
+
+/**
+ * strnlen_user: - Get the size of a user string INCLUDING final NUL.
+ * @str: The string to measure.
+ * @count: Maximum count (including NUL character)
+ *
+ * Context: User context only.  This function may sleep.
+ *
+ * Get the size of a NUL-terminated string in user space.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ * If the string is too long, returns 'count+1'.
+ * On exception (or invalid count), returns 0.
+ */
+long strnlen_user(const char __user *str, long count)
+{
+	unsigned long max_addr, src_addr;
+
+	if (unlikely(count <= 0))
+		return 0;
+
+	max_addr = user_addr_max();
+	src_addr = (unsigned long)str;
+	if (likely(src_addr < max_addr)) {
+		unsigned long max = max_addr - src_addr;
+		return do_strnlen_user(str, count, max);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(strnlen_user);
+
+/**
+ * strlen_user: - Get the size of a user string INCLUDING final NUL.
+ * @str: The string to measure.
+ *
+ * Context: User context only.  This function may sleep.
+ *
+ * Get the size of a NUL-terminated string in user space.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ * On exception, returns 0.
+ *
+ * If there is a limit on the length of a valid string, you may wish to
+ * consider using strnlen_user() instead.
+ */
+long strlen_user(const char __user *str)
+{
+	unsigned long max_addr, src_addr;
+
+	max_addr = user_addr_max();
+	src_addr = (unsigned long)str;
+	if (likely(src_addr < max_addr)) {
+		unsigned long max = max_addr - src_addr;
+		return do_strnlen_user(str, ~0ul, max);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(strlen_user);