[mirror_ubuntu-jammy-kernel.git] / mm / maccess.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Access kernel or user memory without faulting.
 */
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/uaccess.h>

bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
		size_t size)
{
	return true;
}

#ifdef HAVE_GET_KERNEL_NOFAULT

#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label)	\
	while (len >= sizeof(type)) {					\
		__get_kernel_nofault(dst, src, type, err_label);		\
		dst += sizeof(type);					\
		src += sizeof(type);					\
		len -= sizeof(type);					\
	}

long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
	unsigned long align = 0;

	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
		align = (unsigned long)dst | (unsigned long)src;

	if (!copy_from_kernel_nofault_allowed(src, size))
		return -ERANGE;

	pagefault_disable();
	if (!(align & 7))
		copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
	if (!(align & 3))
		copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
	if (!(align & 1))
		copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
	copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
	pagefault_enable();
	return 0;
Efault:
	pagefault_enable();
	return -EFAULT;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label)	\
	while (len >= sizeof(type)) {					\
		__put_kernel_nofault(dst, src, type, err_label);		\
		dst += sizeof(type);					\
		src += sizeof(type);					\
		len -= sizeof(type);					\
	}

long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
	unsigned long align = 0;

	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
		align = (unsigned long)dst | (unsigned long)src;

	pagefault_disable();
	if (!(align & 7))
		copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
	if (!(align & 3))
		copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
	if (!(align & 1))
		copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
	copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
	pagefault_enable();
	return 0;
Efault:
	pagefault_enable();
	return -EFAULT;
}

long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
	const void *src = unsafe_addr;

	if (unlikely(count <= 0))
		return 0;
	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
		return -ERANGE;

	pagefault_disable();
	do {
		__get_kernel_nofault(dst, src, u8, Efault);
		dst++;
		src++;
	} while (dst[-1] && src - unsafe_addr < count);
	pagefault_enable();

	dst[-1] = '\0';
	return src - unsafe_addr;
Efault:
	pagefault_enable();
	dst[-1] = '\0';
	return -EFAULT;
}
#else /* HAVE_GET_KERNEL_NOFAULT */
/**
 * copy_from_kernel_nofault(): safely attempt to read from kernel-space
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from
 * @size: size of the data chunk
 *
 * Safely read from kernel address @src to the buffer at @dst.  If a kernel
 * fault happens, handle that and return -EFAULT.  If @src is not a valid kernel
 * address, return -ERANGE.
 *
 * We ensure that the copy_from_user is executed in atomic context so that
 * do_page_fault() doesn't attempt to take mmap_lock.  This makes
 * copy_from_kernel_nofault() suitable for use within regions where the caller
 * already holds mmap_lock, or other locks which nest inside mmap_lock.
 */
long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
	long ret;
	mm_segment_t old_fs = get_fs();

	if (!copy_from_kernel_nofault_allowed(src, size))
		return -ERANGE;

	set_fs(KERNEL_DS);
	pagefault_disable();
	ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
			size);
	pagefault_enable();
	set_fs(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

/**
 * copy_to_kernel_nofault(): safely attempt to write to a location
 * @dst: address to write to
 * @src: pointer to the data that shall be written
 * @size: size of the data chunk
 *
 * Safely write to address @dst from the buffer at @src.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
	long ret;
	mm_segment_t old_fs = get_fs();

	set_fs(KERNEL_DS);
	pagefault_disable();
	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
	pagefault_enable();
	set_fs(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}

/**
 * strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
 *				 address.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @unsafe_addr: Unsafe address.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from unsafe address to kernel buffer.
 *
 * On success, returns the length of the string INCLUDING the trailing NUL.
 *
 * If access fails, returns -EFAULT (some data may have been copied and the
 * trailing NUL added).  If @unsafe_addr is not a valid kernel address, return
 * -ERANGE.
 *
 * If @count is smaller than the length of the string, copies @count-1 bytes,
 * sets the last byte of @dst buffer to NUL and returns @count.
 */
long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
	mm_segment_t old_fs = get_fs();
	const void *src = unsafe_addr;
	long ret;

	if (unlikely(count <= 0))
		return 0;
	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
		return -ERANGE;

	set_fs(KERNEL_DS);
	pagefault_disable();

	do {
		ret = __get_user(*dst++, (const char __user __force *)src++);
	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);

	dst[-1] = '\0';
	pagefault_enable();
	set_fs(old_fs);

	return ret ? -EFAULT : src - unsafe_addr;
}
#endif /* HAVE_GET_KERNEL_NOFAULT */

/**
 * copy_from_user_nofault(): safely attempt to read from a user-space location
 * @dst: pointer to the buffer that shall take the data
 * @src: address to read from. This must be a user address.
 * @size: size of the data chunk
 *
 * Safely read from user address @src to the buffer at @dst. If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
{
	long ret = -EFAULT;
	mm_segment_t old_fs = force_uaccess_begin();

	if (access_ok(src, size)) {
		pagefault_disable();
		ret = __copy_from_user_inatomic(dst, src, size);
		pagefault_enable();
	}
	force_uaccess_end(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL_GPL(copy_from_user_nofault);

/**
 * copy_to_user_nofault(): safely attempt to write to a user-space location
 * @dst: address to write to
 * @src: pointer to the data that shall be written
 * @size: size of the data chunk
 *
 * Safely write to address @dst from the buffer at @src.  If a kernel fault
 * happens, handle that and return -EFAULT.
 */
long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
{
	long ret = -EFAULT;
	mm_segment_t old_fs = force_uaccess_begin();

	if (access_ok(dst, size)) {
		pagefault_disable();
		ret = __copy_to_user_inatomic(dst, src, size);
		pagefault_enable();
	}
	force_uaccess_end(old_fs);

	if (ret)
		return -EFAULT;
	return 0;
}
EXPORT_SYMBOL_GPL(copy_to_user_nofault);

/**
 * strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
 *				address.
 * @dst:   Destination address, in kernel space.  This buffer must be at
 *         least @count bytes long.
 * @unsafe_addr: Unsafe user address.
 * @count: Maximum number of bytes to copy, including the trailing NUL.
 *
 * Copies a NUL-terminated string from unsafe user address to kernel buffer.
 *
 * On success, returns the length of the string INCLUDING the trailing NUL.
 *
 * If access fails, returns -EFAULT (some data may have been copied
 * and the trailing NUL added).
 *
 * If @count is smaller than the length of the string, copies @count-1 bytes,
 * sets the last byte of @dst buffer to NUL and returns @count.
 */
long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
			      long count)
{
	mm_segment_t old_fs;
	long ret;

	if (unlikely(count <= 0))
		return 0;

	old_fs = force_uaccess_begin();
	pagefault_disable();
	ret = strncpy_from_user(dst, unsafe_addr, count);
	pagefault_enable();
	force_uaccess_end(old_fs);

	if (ret >= count) {
		ret = count;
		dst[ret - 1] = '\0';
	} else if (ret > 0) {
		ret++;
	}

	return ret;
}

/**
 * strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
 * @unsafe_addr: The string to measure.
 * @count: Maximum count (including NUL)
 *
 * Get the size of a NUL-terminated string in user space without pagefault.
 *
 * Returns the size of the string INCLUDING the terminating NUL.
 *
 * If the string is too long, returns a number larger than @count. User
 * has to check the return value against "> count".
 * On exception (or invalid count), returns 0.
 *
 * Unlike strnlen_user, this can be used from IRQ handler etc. because
 * it disables pagefaults.
 */
long strnlen_user_nofault(const void __user *unsafe_addr, long count)
{
	mm_segment_t old_fs;
	int ret;

	old_fs = force_uaccess_begin();
	pagefault_disable();
	ret = strnlen_user(unsafe_addr, count);
	pagefault_enable();
	force_uaccess_end(old_fs);

	return ret;
}
Commit	Line	Data
457c8996	1	// SPDX-License-Identifier: GPL-2.0-only
c33fa9f5	2	/*
3f0acb1e	3	* Access kernel or user memory without faulting.
c33fa9f5	4	*/
b95f1b31	5	#include <linux/export.h>
c33fa9f5	6	#include <linux/mm.h>
7c7fcf76	7	#include <linux/uaccess.h>
c33fa9f5	8
fe557319 CH	9	bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
fe557319 CH	10	size_t size)
eab0c608 CH	11	{
	12	return true;
	13	}
	14
b58294ea CH	15	#ifdef HAVE_GET_KERNEL_NOFAULT
b58294ea CH	16
fe557319	17	#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
b58294ea CH	18	while (len >= sizeof(type)) { \
	19	__get_kernel_nofault(dst, src, type, err_label); \
	20	dst += sizeof(type); \
	21	src += sizeof(type); \
	22	len -= sizeof(type); \
	23	}
	24
fe557319	25	long copy_from_kernel_nofault(void dst, const void src, size_t size)
b58294ea	26	{
2423de2e AB	27	unsigned long align = 0;
	28
	29	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
	30	align = (unsigned long)dst \| (unsigned long)src;
	31
fe557319	32	if (!copy_from_kernel_nofault_allowed(src, size))
2a71e81d	33	return -ERANGE;
b58294ea CH	34
b58294ea CH	35	pagefault_disable();
2423de2e AB	36	if (!(align & 7))
	37	copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
	38	if (!(align & 3))
	39	copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
	40	if (!(align & 1))
	41	copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
fe557319	42	copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
b58294ea CH	43	pagefault_enable();
	44	return 0;
	45	Efault:
	46	pagefault_enable();
	47	return -EFAULT;
	48	}
fe557319	49	EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
b58294ea	50
fe557319	51	#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
b58294ea CH	52	while (len >= sizeof(type)) { \
	53	__put_kernel_nofault(dst, src, type, err_label); \
	54	dst += sizeof(type); \
	55	src += sizeof(type); \
	56	len -= sizeof(type); \
	57	}
	58
fe557319	59	long copy_to_kernel_nofault(void dst, const void src, size_t size)
b58294ea	60	{
2423de2e AB	61	unsigned long align = 0;
	62
	63	if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
	64	align = (unsigned long)dst \| (unsigned long)src;
	65
b58294ea	66	pagefault_disable();
2423de2e AB	67	if (!(align & 7))
	68	copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
	69	if (!(align & 3))
	70	copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
	71	if (!(align & 1))
	72	copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
fe557319	73	copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
b58294ea CH	74	pagefault_enable();
	75	return 0;
	76	Efault:
	77	pagefault_enable();
	78	return -EFAULT;
	79	}
	80
	81	long strncpy_from_kernel_nofault(char dst, const void unsafe_addr, long count)
	82	{
	83	const void *src = unsafe_addr;
	84
	85	if (unlikely(count <= 0))
	86	return 0;
fe557319	87	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
2a71e81d	88	return -ERANGE;
b58294ea CH	89
	90	pagefault_disable();
	91	do {
	92	__get_kernel_nofault(dst, src, u8, Efault);
	93	dst++;
	94	src++;
	95	} while (dst[-1] && src - unsafe_addr < count);
	96	pagefault_enable();
	97
	98	dst[-1] = '\0';
	99	return src - unsafe_addr;
	100	Efault:
	101	pagefault_enable();
	102	dst[-1] = '\0';
	103	return -EFAULT;
	104	}
	105	#else /* HAVE_GET_KERNEL_NOFAULT */
c33fa9f5	106	/**
fe557319	107	* copy_from_kernel_nofault(): safely attempt to read from kernel-space
4f6de12b CH	108	* @dst: pointer to the buffer that shall take the data
	109	* @src: address to read from
	110	* @size: size of the data chunk
	111	*
	112	* Safely read from kernel address @src to the buffer at @dst. If a kernel
2a71e81d CH	113	* fault happens, handle that and return -EFAULT. If @src is not a valid kernel
2a71e81d CH	114	* address, return -ERANGE.
0ab32b6f AM	115	*
0ab32b6f AM	116	* We ensure that the copy_from_user is executed in atomic context so that
c1e8d7c6	117	* do_page_fault() doesn't attempt to take mmap_lock. This makes
fe557319	118	* copy_from_kernel_nofault() suitable for use within regions where the caller
c1e8d7c6	119	* already holds mmap_lock, or other locks which nest inside mmap_lock.
c33fa9f5	120	*/
fe557319	121	long copy_from_kernel_nofault(void dst, const void src, size_t size)
c33fa9f5 IM	122	{
c33fa9f5 IM	123	long ret;
b4b8ac52	124	mm_segment_t old_fs = get_fs();
c33fa9f5	125
fe557319	126	if (!copy_from_kernel_nofault_allowed(src, size))
2a71e81d	127	return -ERANGE;
eab0c608	128
b4b8ac52	129	set_fs(KERNEL_DS);
cd030905 CH	130	pagefault_disable();
	131	ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
	132	size);
	133	pagefault_enable();
b4b8ac52	134	set_fs(old_fs);
c33fa9f5	135
cd030905 CH	136	if (ret)
	137	return -EFAULT;
	138	return 0;
c33fa9f5	139	}
fe557319	140	EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
c33fa9f5 IM	141
c33fa9f5 IM	142	/**
fe557319	143	* copy_to_kernel_nofault(): safely attempt to write to a location
c33fa9f5 IM	144	* @dst: address to write to
	145	* @src: pointer to the data that shall be written
	146	* @size: size of the data chunk
	147	*
	148	* Safely write to address @dst from the buffer at @src. If a kernel fault
	149	* happens, handle that and return -EFAULT.
	150	*/
fe557319	151	long copy_to_kernel_nofault(void dst, const void src, size_t size)
c33fa9f5 IM	152	{
c33fa9f5 IM	153	long ret;
b4b8ac52	154	mm_segment_t old_fs = get_fs();
c33fa9f5	155
b4b8ac52	156	set_fs(KERNEL_DS);
cd030905 CH	157	pagefault_disable();
	158	ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
	159	pagefault_enable();
b4b8ac52	160	set_fs(old_fs);
c33fa9f5	161
cd030905 CH	162	if (ret)
	163	return -EFAULT;
	164	return 0;
c33fa9f5	165	}
dbb7ee0e	166
4f6de12b	167	/**
c4cb1644	168	* strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
4f6de12b CH	169	* address.
	170	* @dst: Destination address, in kernel space. This buffer must be at
	171	* least @count bytes long.
	172	* @unsafe_addr: Unsafe address.
	173	* @count: Maximum number of bytes to copy, including the trailing NUL.
	174	*
	175	* Copies a NUL-terminated string from unsafe address to kernel buffer.
	176	*
	177	* On success, returns the length of the string INCLUDING the trailing NUL.
	178	*
2a71e81d CH	179	* If access fails, returns -EFAULT (some data may have been copied and the
	180	* trailing NUL added). If @unsafe_addr is not a valid kernel address, return
	181	* -ERANGE.
4f6de12b CH	182	*
	183	* If @count is smaller than the length of the string, copies @count-1 bytes,
	184	* sets the last byte of @dst buffer to NUL and returns @count.
	185	*/
eab0c608	186	long strncpy_from_kernel_nofault(char dst, const void unsafe_addr, long count)
dbb7ee0e AS	187	{
	188	mm_segment_t old_fs = get_fs();
	189	const void *src = unsafe_addr;
	190	long ret;
	191
	192	if (unlikely(count <= 0))
	193	return 0;
fe557319	194	if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
2a71e81d	195	return -ERANGE;
dbb7ee0e AS	196
	197	set_fs(KERNEL_DS);
	198	pagefault_disable();
	199
	200	do {
bd28b145	201	ret = __get_user(dst++, (const char __user __force )src++);
dbb7ee0e AS	202	} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
	203
	204	dst[-1] = '\0';
	205	pagefault_enable();
	206	set_fs(old_fs);
	207
9dd861d5	208	return ret ? -EFAULT : src - unsafe_addr;
dbb7ee0e	209	}
b58294ea	210	#endif /* HAVE_GET_KERNEL_NOFAULT */
3d708182	211
fc3562d7	212	/**
c0ee37e8	213	* copy_from_user_nofault(): safely attempt to read from a user-space location
fc3562d7 CH	214	* @dst: pointer to the buffer that shall take the data
	215	* @src: address to read from. This must be a user address.
	216	* @size: size of the data chunk
	217	*
	218	* Safely read from user address @src to the buffer at @dst. If a kernel fault
	219	* happens, handle that and return -EFAULT.
	220	*/
c0ee37e8	221	long copy_from_user_nofault(void dst, const void __user src, size_t size)
fc3562d7 CH	222	{
fc3562d7 CH	223	long ret = -EFAULT;
3d13f313	224	mm_segment_t old_fs = force_uaccess_begin();
fc3562d7	225
fc3562d7 CH	226	if (access_ok(src, size)) {
	227	pagefault_disable();
	228	ret = __copy_from_user_inatomic(dst, src, size);
	229	pagefault_enable();
	230	}
3d13f313	231	force_uaccess_end(old_fs);
fc3562d7 CH	232
	233	if (ret)
	234	return -EFAULT;
	235	return 0;
	236	}
c0ee37e8	237	EXPORT_SYMBOL_GPL(copy_from_user_nofault);
fc3562d7 CH	238
fc3562d7 CH	239	/**
c0ee37e8	240	* copy_to_user_nofault(): safely attempt to write to a user-space location
fc3562d7 CH	241	* @dst: address to write to
	242	* @src: pointer to the data that shall be written
	243	* @size: size of the data chunk
	244	*
	245	* Safely write to address @dst from the buffer at @src. If a kernel fault
	246	* happens, handle that and return -EFAULT.
	247	*/
c0ee37e8	248	long copy_to_user_nofault(void __user dst, const void src, size_t size)
fc3562d7 CH	249	{
fc3562d7 CH	250	long ret = -EFAULT;
3d13f313	251	mm_segment_t old_fs = force_uaccess_begin();
fc3562d7	252
fc3562d7 CH	253	if (access_ok(dst, size)) {
	254	pagefault_disable();
	255	ret = __copy_to_user_inatomic(dst, src, size);
	256	pagefault_enable();
	257	}
3d13f313	258	force_uaccess_end(old_fs);
fc3562d7 CH	259
	260	if (ret)
	261	return -EFAULT;
	262	return 0;
	263	}
c0ee37e8	264	EXPORT_SYMBOL_GPL(copy_to_user_nofault);
fc3562d7	265
3d708182	266	/**
bd88bb5d	267	* strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
3d708182 MH	268	* address.
	269	* @dst: Destination address, in kernel space. This buffer must be at
	270	* least @count bytes long.
	271	* @unsafe_addr: Unsafe user address.
	272	* @count: Maximum number of bytes to copy, including the trailing NUL.
	273	*
	274	* Copies a NUL-terminated string from unsafe user address to kernel buffer.
	275	*
	276	* On success, returns the length of the string INCLUDING the trailing NUL.
	277	*
	278	* If access fails, returns -EFAULT (some data may have been copied
	279	* and the trailing NUL added).
	280	*
	281	* If @count is smaller than the length of the string, copies @count-1 bytes,
	282	* sets the last byte of @dst buffer to NUL and returns @count.
	283	*/
bd88bb5d	284	long strncpy_from_user_nofault(char dst, const void __user unsafe_addr,
3d708182 MH	285	long count)
3d708182 MH	286	{
3d13f313	287	mm_segment_t old_fs;
3d708182 MH	288	long ret;
	289
	290	if (unlikely(count <= 0))
	291	return 0;
	292
3d13f313	293	old_fs = force_uaccess_begin();
3d708182 MH	294	pagefault_disable();
	295	ret = strncpy_from_user(dst, unsafe_addr, count);
	296	pagefault_enable();
3d13f313	297	force_uaccess_end(old_fs);
3d708182 MH	298
	299	if (ret >= count) {
	300	ret = count;
	301	dst[ret - 1] = '\0';
	302	} else if (ret > 0) {
	303	ret++;
	304	}
	305
	306	return ret;
	307	}
	308
	309	/**
02dddb16	310	* strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
3d708182 MH	311	* @unsafe_addr: The string to measure.
	312	* @count: Maximum count (including NUL)
	313	*
	314	* Get the size of a NUL-terminated string in user space without pagefault.
	315	*
	316	* Returns the size of the string INCLUDING the terminating NUL.
	317	*
	318	* If the string is too long, returns a number larger than @count. User
	319	* has to check the return value against "> count".
	320	* On exception (or invalid count), returns 0.
	321	*
	322	* Unlike strnlen_user, this can be used from IRQ handler etc. because
	323	* it disables pagefaults.
	324	*/
02dddb16	325	long strnlen_user_nofault(const void __user *unsafe_addr, long count)
3d708182	326	{
3d13f313	327	mm_segment_t old_fs;
3d708182 MH	328	int ret;
3d708182 MH	329
3d13f313	330	old_fs = force_uaccess_begin();
3d708182 MH	331	pagefault_disable();
	332	ret = strnlen_user(unsafe_addr, count);
	333	pagefault_enable();
3d13f313	334	force_uaccess_end(old_fs);
3d708182 MH	335
	336	return ret;
	337	}