lib/checksum.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *
   4  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   5  *              operating system.  INET is implemented using the  BSD Socket
   6  *              interface as the means of communication with the user level.
   7  *
   8  *              IP/TCP/UDP checksumming routines
   9  *
  10  * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
  11  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  12  *              Tom May, <ftom@netcom.com>
  13  *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
  14  *              Lots of code moved from tcp.c and ip.c; see those files
  15  *              for more names.
  16  *
  17  * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
  18  *              Fixed some nasty bugs, causing some horrible crashes.
  19  *              A: At some points, the sum (%0) was used as
  20  *              length-counter instead of the length counter
  21  *              (%1). Thanks to Roman Hodek for pointing this out.
  22  *              B: GCC seems to mess up if one uses too many
  23  *              data-registers to hold input values and one tries to
  24  *              specify d0 and d1 as scratch registers. Letting gcc
  25  *              choose these registers itself solves the problem.
  26  */
  27
  28 /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
  29  kills, so most of the assembly has to go. */
  30
  31 #include <linux/export.h>
  32 #include <net/checksum.h>
  33
  34 #include <asm/byteorder.h>
  35
  36 #ifndef do_csum
  37 static unsigned int do_csum(const unsigned char *buff, int len)
  38 {
  39         int odd;
  40         unsigned int result = 0;
  41
  42         if (len <= 0)
  43                 goto out;
  44         odd = 1 & (unsigned long) buff;
  45         if (odd) {
  46 #ifdef __LITTLE_ENDIAN
  47                 result += (*buff << 8);
  48 #else
  49                 result = *buff;
  50 #endif
  51                 len--;
  52                 buff++;
  53         }
  54         if (len >= 2) {
  55                 if (2 & (unsigned long) buff) {
  56                         result += *(unsigned short *) buff;
  57                         len -= 2;
  58                         buff += 2;
  59                 }
  60                 if (len >= 4) {
  61                         const unsigned char *end = buff + ((unsigned)len & ~3);
  62                         unsigned int carry = 0;
  63                         do {
  64                                 unsigned int w = *(unsigned int *) buff;
  65                                 buff += 4;
  66                                 result += carry;
  67                                 result += w;
  68                                 carry = (w > result);
  69                         } while (buff < end);
  70                         result += carry;
  71                         result = (result & 0xffff) + (result >> 16);
  72                 }
  73                 if (len & 2) {
  74                         result += *(unsigned short *) buff;
  75                         buff += 2;
  76                 }
  77         }
  78         if (len & 1)
  79 #ifdef __LITTLE_ENDIAN
  80                 result += *buff;
  81 #else
  82                 result += (*buff << 8);
  83 #endif
  84         result = csum_from32to16(result);
  85         if (odd)
  86                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  87 out:
  88         return result;
  89 }
  90 #endif
  91
  92 #ifndef ip_fast_csum
  93 /*
  94  *      This is a version of ip_compute_csum() optimized for IP headers,
  95  *      which always checksum on 4 octet boundaries.
  96  */
  97 __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
  98 {
  99         return (__force __sum16)~do_csum(iph, ihl*4);
 100 }
 101 EXPORT_SYMBOL(ip_fast_csum);
 102 #endif
 103
 104 /*
 105  * computes the checksum of a memory block at buff, length len,
 106  * and adds in "sum" (32-bit)
 107  *
 108  * returns a 32-bit number suitable for feeding into itself
 109  * or csum_tcpudp_magic
 110  *
 111  * this function must be called with even lengths, except
 112  * for the last fragment, which may be odd
 113  *
 114  * it's best to have buff aligned on a 32-bit boundary
 115  */
 116 __wsum csum_partial(const void *buff, int len, __wsum wsum)
 117 {
 118         unsigned int sum = (__force unsigned int)wsum;
 119         unsigned int result = do_csum(buff, len);
 120
 121         /* add in old sum, and carry.. */
 122         result += sum;
 123         if (sum > result)
 124                 result += 1;
 125         return (__force __wsum)result;
 126 }
 127 EXPORT_SYMBOL(csum_partial);
 128
 129 /*
 130  * this routine is used for miscellaneous IP-like checksums, mainly
 131  * in icmp.c
 132  */
 133 __sum16 ip_compute_csum(const void *buff, int len)
 134 {
 135         return (__force __sum16)~do_csum(buff, len);
 136 }
 137 EXPORT_SYMBOL(ip_compute_csum);
 138
 139 #ifndef csum_tcpudp_nofold
 140 static inline u32 from64to32(u64 x)
 141 {
 142         /* add up 32-bit and 32-bit for 32+c bit */
 143         x = (x & 0xffffffff) + (x >> 32);
 144         /* add up carry.. */
 145         x = (x & 0xffffffff) + (x >> 32);
 146         return (u32)x;
 147 }
 148
 149 __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 150                           __u32 len, __u8 proto, __wsum sum)
 151 {
 152         unsigned long long s = (__force u32)sum;
 153
 154         s += (__force u32)saddr;
 155         s += (__force u32)daddr;
 156 #ifdef __BIG_ENDIAN
 157         s += proto + len;
 158 #else
 159         s += (proto + len) << 8;
 160 #endif
 161         return (__force __wsum)from64to32(s);
 162 }
 163 EXPORT_SYMBOL(csum_tcpudp_nofold);
 164 #endif