1 /* 2 * User address space access functions. 3 * 4 * For licencing details see kernel-base/COPYING 5 */ 6 7 #include <linux/highmem.h> 8 #include <linux/module.h> 9 10 #include <asm/word-at-a-time.h> 11 12 /* 13 * best effort, GUP based copy_from_user() that is NMI-safe 14 */ 15 unsigned long 16 copy_from_user_nmi(void *to, const void __user *from, unsigned long n) 17 { 18 unsigned long offset, addr = (unsigned long)from; 19 unsigned long size, len = 0; 20 struct page *page; 21 void *map; 22 int ret; 23 24 do { 25 ret = __get_user_pages_fast(addr, 1, 0, &page); 26 if (!ret) 27 break; 28 29 offset = addr & (PAGE_SIZE - 1); 30 size = min(PAGE_SIZE - offset, n - len); 31 32 map = kmap_atomic(page); 33 memcpy(to, map+offset, size); 34 kunmap_atomic(map); 35 put_page(page); 36 37 len += size; 38 to += size; 39 addr += size; 40 41 } while (len < n); 42 43 return len; 44 } 45 EXPORT_SYMBOL_GPL(copy_from_user_nmi); 46 47 static inline unsigned long count_bytes(unsigned long mask) 48 { 49 mask = (mask - 1) & ~mask; 50 mask >>= 7; 51 return count_masked_bytes(mask); 52 } 53 54 /* 55 * Do a strncpy, return length of string without final '\0'. 56 * 'count' is the user-supplied count (return 'count' if we 57 * hit it), 'max' is the address space maximum (and we return 58 * -EFAULT if we hit it). 59 */ 60 static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) 61 { 62 long res = 0; 63 64 /* 65 * Truncate 'max' to the user-specified limit, so that 66 * we only have one limit we need to check in the loop 67 */ 68 if (max > count) 69 max = count; 70 71 while (max >= sizeof(unsigned long)) { 72 unsigned long c; 73 74 /* Fall back to byte-at-a-time if we get a page fault */ 75 if (unlikely(__get_user(c,(unsigned long __user *)(src+res)))) 76 break; 77 /* This can write a few bytes past the NUL character, but that's ok */ 78 *(unsigned long *)(dst+res) = c; 79 c = has_zero(c); 80 if (c) 81 return res + count_bytes(c); 82 res += sizeof(unsigned long); 83 max -= sizeof(unsigned long); 84 } 85 86 while (max) { 87 char c; 88 89 if (unlikely(__get_user(c,src+res))) 90 return -EFAULT; 91 dst[res] = c; 92 if (!c) 93 return res; 94 res++; 95 max--; 96 } 97 98 /* 99 * Uhhuh. We hit 'max'. But was that the user-specified maximum 100 * too? If so, that's ok - we got as much as the user asked for. 101 */ 102 if (res >= count) 103 return res; 104 105 /* 106 * Nope: we hit the address space limit, and we still had more 107 * characters the caller would have wanted. That's an EFAULT. 108 */ 109 return -EFAULT; 110 } 111 112 /** 113 * strncpy_from_user: - Copy a NUL terminated string from userspace. 114 * @dst: Destination address, in kernel space. This buffer must be at 115 * least @count bytes long. 116 * @src: Source address, in user space. 117 * @count: Maximum number of bytes to copy, including the trailing NUL. 118 * 119 * Copies a NUL-terminated string from userspace to kernel space. 120 * 121 * On success, returns the length of the string (not including the trailing 122 * NUL). 123 * 124 * If access to userspace fails, returns -EFAULT (some data may have been 125 * copied). 126 * 127 * If @count is smaller than the length of the string, copies @count bytes 128 * and returns @count. 129 */ 130 long 131 strncpy_from_user(char *dst, const char __user *src, long count) 132 { 133 unsigned long max_addr, src_addr; 134 135 if (unlikely(count <= 0)) 136 return 0; 137 138 max_addr = current_thread_info()->addr_limit.seg; 139 src_addr = (unsigned long)src; 140 if (likely(src_addr < max_addr)) { 141 unsigned long max = max_addr - src_addr; 142 return do_strncpy_from_user(dst, src, count, max); 143 } 144 return -EFAULT; 145 } 146 EXPORT_SYMBOL(strncpy_from_user); 147