9fd4470ff4
This converts the generic user string functions to use the batched user access functions. It makes a big difference on Skylake, which is the first x86 microarchitecture to implement SMAP. The STAC/CLAC instructions are not very fast, and doing them for each access inside the loop that copies strings from user space (which is what the pathname handling does for every pathname the kernel uses, for example) is very inefficient. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
120 lines
3 KiB
C
120 lines
3 KiB
C
#include <linux/compiler.h>
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#include <linux/export.h>
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#include <linux/uaccess.h>
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#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <asm/byteorder.h>
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#include <asm/word-at-a-time.h>
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#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
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#define IS_UNALIGNED(src, dst) 0
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#else
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#define IS_UNALIGNED(src, dst) \
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(((long) dst | (long) src) & (sizeof(long) - 1))
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#endif
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/*
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* Do a strncpy, return length of string without final '\0'.
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* 'count' is the user-supplied count (return 'count' if we
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* hit it), 'max' is the address space maximum (and we return
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* -EFAULT if we hit it).
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*/
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static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max)
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{
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const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
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long res = 0;
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/*
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* Truncate 'max' to the user-specified limit, so that
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* we only have one limit we need to check in the loop
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*/
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if (max > count)
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max = count;
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if (IS_UNALIGNED(src, dst))
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goto byte_at_a_time;
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while (max >= sizeof(unsigned long)) {
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unsigned long c, data;
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/* Fall back to byte-at-a-time if we get a page fault */
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if (unlikely(unsafe_get_user(c,(unsigned long __user *)(src+res))))
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break;
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*(unsigned long *)(dst+res) = c;
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if (has_zero(c, &data, &constants)) {
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data = prep_zero_mask(c, data, &constants);
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data = create_zero_mask(data);
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return res + find_zero(data);
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}
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res += sizeof(unsigned long);
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max -= sizeof(unsigned long);
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}
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byte_at_a_time:
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while (max) {
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char c;
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if (unlikely(unsafe_get_user(c,src+res)))
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return -EFAULT;
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dst[res] = c;
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if (!c)
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return res;
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res++;
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max--;
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}
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/*
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* Uhhuh. We hit 'max'. But was that the user-specified maximum
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* too? If so, that's ok - we got as much as the user asked for.
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*/
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if (res >= count)
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return res;
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/*
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* Nope: we hit the address space limit, and we still had more
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* characters the caller would have wanted. That's an EFAULT.
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*/
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return -EFAULT;
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}
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/**
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* strncpy_from_user: - Copy a NUL terminated string from userspace.
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* @dst: Destination address, in kernel space. This buffer must be at
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* least @count bytes long.
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* @src: Source address, in user space.
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* @count: Maximum number of bytes to copy, including the trailing NUL.
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*
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* Copies a NUL-terminated string from userspace to kernel space.
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*
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* On success, returns the length of the string (not including the trailing
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* NUL).
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*
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* If access to userspace fails, returns -EFAULT (some data may have been
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* copied).
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*
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* If @count is smaller than the length of the string, copies @count bytes
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* and returns @count.
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*/
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long strncpy_from_user(char *dst, const char __user *src, long count)
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{
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unsigned long max_addr, src_addr;
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if (unlikely(count <= 0))
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return 0;
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max_addr = user_addr_max();
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src_addr = (unsigned long)src;
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if (likely(src_addr < max_addr)) {
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unsigned long max = max_addr - src_addr;
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long retval;
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user_access_begin();
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retval = do_strncpy_from_user(dst, src, count, max);
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user_access_end();
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return retval;
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}
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return -EFAULT;
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}
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EXPORT_SYMBOL(strncpy_from_user);
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