Commit 4ae73f2d authored by Linus Torvalds's avatar Linus Torvalds
Browse files

x86: use generic strncpy_from_user routine 



The generic strncpy_from_user() is not really optimal, since it is
designed to work on both little-endian and big-endian.  And on
little-endian you can simplify much of the logic to find the first zero
byte, since little-endian arithmetic doesn't have to worry about the
carry bit propagating into earlier bytes (only later bytes, which we
don't care about).

But I have patches to make the generic routines use the architecture-
specific <asm/word-at-a-time.h> infrastructure, so that we can regain
the little-endian optimizations.  But before we do that, switch over to
the generic routines to make the patches each do just one well-defined
thing.

Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent da89fb16

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -93,6 +93,7 @@ config X86 
	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



config INSTRUCTION_DECODER

	def_bool (KPROBES || PERF_EVENTS || UPROBES)

arch/x86/include/asm/uaccess.h

+1 −0
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ 


#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))

arch/x86/lib/usercopy.c

+0 −97
Original line number Diff line number Diff line
@@ -43,100 +43,3 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n) 
	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);

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