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x86: use generic strncpy_from_user routine

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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: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2012-05-26 10:14:39 -07:00
parent da89fb165e
commit 4ae73f2d53
3 changed files with 2 additions and 97 deletions
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1
arch/x86/Kconfig
View File

@ -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)

1
arch/x86/include/asm/uaccess.h
View File

@ -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))

97
arch/x86/lib/usercopy.c
View File

@ -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);