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 inline unsigned short from32to16(unsigned int x)
  38 {
  39         /* add up 16-bit and 16-bit for 16+c bit */
  40         x = (x & 0xffff) + (x >> 16);
  41         /* add up carry.. */
  42         x = (x & 0xffff) + (x >> 16);
  43         return x;
  44 }
  45
  46 static unsigned int do_csum(const unsigned char *buff, int len)
  47 {
  48         int odd;
  49         unsigned int result = 0;
  50
  51         if (len <= 0)
  52                 goto out;
  53         odd = 1 & (unsigned long) buff;
  54         if (odd) {
  55 #ifdef __LITTLE_ENDIAN
  56                 result += (*buff << 8);
  57 #else
  58                 result = *buff;
  59 #endif
  60                 len--;
  61                 buff++;
  62         }
  63         if (len >= 2) {
  64                 if (2 & (unsigned long) buff) {
  65                         result += *(unsigned short *) buff;
  66                         len -= 2;
  67                         buff += 2;
  68                 }
  69                 if (len >= 4) {
  70                         const unsigned char *end = buff + ((unsigned)len & ~3);
  71                         unsigned int carry = 0;
  72                         do {
  73                                 unsigned int w = *(unsigned int *) buff;
  74                                 buff += 4;
  75                                 result += carry;
  76                                 result += w;
  77                                 carry = (w > result);
  78                         } while (buff < end);
  79                         result += carry;
  80                         result = (result & 0xffff) + (result >> 16);
  81                 }
  82                 if (len & 2) {
  83                         result += *(unsigned short *) buff;
  84                         buff += 2;
  85                 }
  86         }
  87         if (len & 1)
  88 #ifdef __LITTLE_ENDIAN
  89                 result += *buff;
  90 #else
  91                 result += (*buff << 8);
  92 #endif
  93         result = from32to16(result);
  94         if (odd)
  95                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  96 out:
  97         return result;
  98 }
  99 #endif
 100
 101 #ifndef ip_fast_csum
 102 /*
 103  *      This is a version of ip_compute_csum() optimized for IP headers,
 104  *      which always checksum on 4 octet boundaries.
 105  */
 106 __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 107 {
 108         return (__force __sum16)~do_csum(iph, ihl*4);
 109 }
 110 EXPORT_SYMBOL(ip_fast_csum);
 111 #endif
 112
 113 /*
 114  * computes the checksum of a memory block at buff, length len,
 115  * and adds in "sum" (32-bit)
 116  *
 117  * returns a 32-bit number suitable for feeding into itself
 118  * or csum_tcpudp_magic
 119  *
 120  * this function must be called with even lengths, except
 121  * for the last fragment, which may be odd
 122  *
 123  * it's best to have buff aligned on a 32-bit boundary
 124  */
 125 __wsum csum_partial(const void *buff, int len, __wsum wsum)
 126 {
 127         unsigned int sum = (__force unsigned int)wsum;
 128         unsigned int result = do_csum(buff, len);
 129
 130         /* add in old sum, and carry.. */
 131         result += sum;
 132         if (sum > result)
 133                 result += 1;
 134         return (__force __wsum)result;
 135 }
 136 EXPORT_SYMBOL(csum_partial);
 137
 138 /*
 139  * this routine is used for miscellaneous IP-like checksums, mainly
 140  * in icmp.c
 141  */
 142 __sum16 ip_compute_csum(const void *buff, int len)
 143 {
 144         return (__force __sum16)~do_csum(buff, len);
 145 }
 146 EXPORT_SYMBOL(ip_compute_csum);
 147
 148 #ifndef csum_tcpudp_nofold
 149 static inline u32 from64to32(u64 x)
 150 {
 151         /* add up 32-bit and 32-bit for 32+c bit */
 152         x = (x & 0xffffffff) + (x >> 32);
 153         /* add up carry.. */
 154         x = (x & 0xffffffff) + (x >> 32);
 155         return (u32)x;
 156 }
 157
 158 __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 159                           __u32 len, __u8 proto, __wsum sum)
 160 {
 161         unsigned long long s = (__force u32)sum;
 162
 163         s += (__force u32)saddr;
 164         s += (__force u32)daddr;
 165 #ifdef __BIG_ENDIAN
 166         s += proto + len;
 167 #else
 168         s += (proto + len) << 8;
 169 #endif
 170         return (__force __wsum)from64to32(s);
 171 }
 172 EXPORT_SYMBOL(csum_tcpudp_nofold);
 173 #endif