lib/mpi/mpicoder.c

   1 /* mpicoder.c  -  Coder for the external representation of MPIs
   2  * Copyright (C) 1998, 1999 Free Software Foundation, Inc.
   3  *
   4  * This file is part of GnuPG.
   5  *
   6  * GnuPG is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * GnuPG is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19  */
  20
  21 #include <linux/bitops.h>
  22 #include <linux/count_zeros.h>
  23 #include <linux/byteorder/generic.h>
  24 #include <linux/scatterlist.h>
  25 #include <linux/string.h>
  26 #include "mpi-internal.h"
  27
  28 #define MAX_EXTERN_MPI_BITS 16384
  29
  30 /**
  31  * mpi_read_raw_data - Read a raw byte stream as a positive integer
  32  * @xbuffer: The data to read
  33  * @nbytes: The amount of data to read
  34  */
  35 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
  36 {
  37         const uint8_t *buffer = xbuffer;
  38         int i, j;
  39         unsigned nbits, nlimbs;
  40         mpi_limb_t a;
  41         MPI val = NULL;
  42
  43         while (nbytes > 0 && buffer[0] == 0) {
  44                 buffer++;
  45                 nbytes--;
  46         }
  47
  48         nbits = nbytes * 8;
  49         if (nbits > MAX_EXTERN_MPI_BITS) {
  50                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  51                 return NULL;
  52         }
  53         if (nbytes > 0)
  54                 nbits -= count_leading_zeros(buffer[0]) - (BITS_PER_LONG - 8);
  55
  56         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
  57         val = mpi_alloc(nlimbs);
  58         if (!val)
  59                 return NULL;
  60         val->nbits = nbits;
  61         val->sign = 0;
  62         val->nlimbs = nlimbs;
  63
  64         if (nbytes > 0) {
  65                 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
  66                 i %= BYTES_PER_MPI_LIMB;
  67                 for (j = nlimbs; j > 0; j--) {
  68                         a = 0;
  69                         for (; i < BYTES_PER_MPI_LIMB; i++) {
  70                                 a <<= 8;
  71                                 a |= *buffer++;
  72                         }
  73                         i = 0;
  74                         val->d[j - 1] = a;
  75                 }
  76         }
  77         return val;
  78 }
  79 EXPORT_SYMBOL_GPL(mpi_read_raw_data);
  80
  81 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
  82 {
  83         const uint8_t *buffer = xbuffer;
  84         unsigned int nbits, nbytes;
  85         MPI val;
  86
  87         if (*ret_nread < 2)
  88                 return ERR_PTR(-EINVAL);
  89         nbits = buffer[0] << 8 | buffer[1];
  90
  91         if (nbits > MAX_EXTERN_MPI_BITS) {
  92                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  93                 return ERR_PTR(-EINVAL);
  94         }
  95
  96         nbytes = DIV_ROUND_UP(nbits, 8);
  97         if (nbytes + 2 > *ret_nread) {
  98                 pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
  99                                 nbytes, *ret_nread);
 100                 return ERR_PTR(-EINVAL);
 101         }
 102
 103         val = mpi_read_raw_data(buffer + 2, nbytes);
 104         if (!val)
 105                 return ERR_PTR(-ENOMEM);
 106
 107         *ret_nread = nbytes + 2;
 108         return val;
 109 }
 110 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 111
 112 static int count_lzeros(MPI a)
 113 {
 114         mpi_limb_t alimb;
 115         int i, lzeros = 0;
 116
 117         for (i = a->nlimbs - 1; i >= 0; i--) {
 118                 alimb = a->d[i];
 119                 if (alimb == 0) {
 120                         lzeros += sizeof(mpi_limb_t);
 121                 } else {
 122                         lzeros += count_leading_zeros(alimb) / 8;
 123                         break;
 124                 }
 125         }
 126         return lzeros;
 127 }
 128
 129 /**
 130  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 131  *
 132  * @a:          a multi precision integer
 133  * @buf:        bufer to which the output will be written to. Needs to be at
 134  *              leaset mpi_get_size(a) long.
 135  * @buf_len:    size of the buf.
 136  * @nbytes:     receives the actual length of the data written on success and
 137  *              the data to-be-written on -EOVERFLOW in case buf_len was too
 138  *              small.
 139  * @sign:       if not NULL, it will be set to the sign of a.
 140  *
 141  * Return:      0 on success or error code in case of error
 142  */
 143 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 144                     int *sign)
 145 {
 146         uint8_t *p;
 147 #if BYTES_PER_MPI_LIMB == 4
 148         __be32 alimb;
 149 #elif BYTES_PER_MPI_LIMB == 8
 150         __be64 alimb;
 151 #else
 152 #error please implement for this limb size.
 153 #endif
 154         unsigned int n = mpi_get_size(a);
 155         int i, lzeros;
 156
 157         if (!buf || !nbytes)
 158                 return -EINVAL;
 159
 160         if (sign)
 161                 *sign = a->sign;
 162
 163         lzeros = count_lzeros(a);
 164
 165         if (buf_len < n - lzeros) {
 166                 *nbytes = n - lzeros;
 167                 return -EOVERFLOW;
 168         }
 169
 170         p = buf;
 171         *nbytes = n - lzeros;
 172
 173         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 174                         lzeros %= BYTES_PER_MPI_LIMB;
 175                 i >= 0; i--) {
 176 #if BYTES_PER_MPI_LIMB == 4
 177                 alimb = cpu_to_be32(a->d[i]);
 178 #elif BYTES_PER_MPI_LIMB == 8
 179                 alimb = cpu_to_be64(a->d[i]);
 180 #else
 181 #error please implement for this limb size.
 182 #endif
 183                 memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
 184                 p += BYTES_PER_MPI_LIMB - lzeros;
 185                 lzeros = 0;
 186         }
 187         return 0;
 188 }
 189 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 190
 191 /*
 192  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 193  * Caller must free the return string.
 194  * This function does return a 0 byte buffer with nbytes set to zero if the
 195  * value of A is zero.
 196  *
 197  * @a:          a multi precision integer.
 198  * @nbytes:     receives the length of this buffer.
 199  * @sign:       if not NULL, it will be set to the sign of the a.
 200  *
 201  * Return:      Pointer to MPI buffer or NULL on error
 202  */
 203 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 204 {
 205         uint8_t *buf;
 206         unsigned int n;
 207         int ret;
 208
 209         if (!nbytes)
 210                 return NULL;
 211
 212         n = mpi_get_size(a);
 213
 214         if (!n)
 215                 n++;
 216
 217         buf = kmalloc(n, GFP_KERNEL);
 218
 219         if (!buf)
 220                 return NULL;
 221
 222         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 223
 224         if (ret) {
 225                 kfree(buf);
 226                 return NULL;
 227         }
 228         return buf;
 229 }
 230 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 231
 232 /**
 233  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 234  *
 235  * This function works in the same way as the mpi_read_buffer, but it
 236  * takes an sgl instead of u8 * buf.
 237  *
 238  * @a:          a multi precision integer
 239  * @sgl:        scatterlist to write to. Needs to be at least
 240  *              mpi_get_size(a) long.
 241  * @nbytes:     the number of bytes to write.  Leading bytes will be
 242  *              filled with zero.
 243  * @sign:       if not NULL, it will be set to the sign of a.
 244  *
 245  * Return:      0 on success or error code in case of error
 246  */
 247 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned nbytes,
 248                      int *sign)
 249 {
 250         u8 *p, *p2;
 251 #if BYTES_PER_MPI_LIMB == 4
 252         __be32 alimb;
 253 #elif BYTES_PER_MPI_LIMB == 8
 254         __be64 alimb;
 255 #else
 256 #error please implement for this limb size.
 257 #endif
 258         unsigned int n = mpi_get_size(a);
 259         struct sg_mapping_iter miter;
 260         int i, x, buf_len;
 261         int nents;
 262
 263         if (sign)
 264                 *sign = a->sign;
 265
 266         if (nbytes < n)
 267                 return -EOVERFLOW;
 268
 269         nents = sg_nents_for_len(sgl, nbytes);
 270         if (nents < 0)
 271                 return -EINVAL;
 272
 273         sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
 274         sg_miter_next(&miter);
 275         buf_len = miter.length;
 276         p2 = miter.addr;
 277
 278         while (nbytes > n) {
 279                 i = min_t(unsigned, nbytes - n, buf_len);
 280                 memset(p2, 0, i);
 281                 p2 += i;
 282                 nbytes -= i;
 283
 284                 buf_len -= i;
 285                 if (!buf_len) {
 286                         sg_miter_next(&miter);
 287                         buf_len = miter.length;
 288                         p2 = miter.addr;
 289                 }
 290         }
 291
 292         for (i = a->nlimbs - 1; i >= 0; i--) {
 293 #if BYTES_PER_MPI_LIMB == 4
 294                 alimb = a->d[i] ? cpu_to_be32(a->d[i]) : 0;
 295 #elif BYTES_PER_MPI_LIMB == 8
 296                 alimb = a->d[i] ? cpu_to_be64(a->d[i]) : 0;
 297 #else
 298 #error please implement for this limb size.
 299 #endif
 300                 p = (u8 *)&alimb;
 301
 302                 for (x = 0; x < sizeof(alimb); x++) {
 303                         *p2++ = *p++;
 304                         if (!--buf_len) {
 305                                 sg_miter_next(&miter);
 306                                 buf_len = miter.length;
 307                                 p2 = miter.addr;
 308                         }
 309                 }
 310         }
 311
 312         sg_miter_stop(&miter);
 313         return 0;
 314 }
 315 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 316
 317 /*
 318  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 319  *                           data from the sgl
 320  *
 321  * This function works in the same way as the mpi_read_raw_data, but it
 322  * takes an sgl instead of void * buffer. i.e. it allocates
 323  * a new MPI and reads the content of the sgl to the MPI.
 324  *
 325  * @sgl:        scatterlist to read from
 326  * @nbytes:     number of bytes to read
 327  *
 328  * Return:      Pointer to a new MPI or NULL on error
 329  */
 330 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 331 {
 332         struct sg_mapping_iter miter;
 333         unsigned int nbits, nlimbs;
 334         int x, j, z, lzeros, ents;
 335         unsigned int len;
 336         const u8 *buff;
 337         mpi_limb_t a;
 338         MPI val = NULL;
 339
 340         ents = sg_nents_for_len(sgl, nbytes);
 341         if (ents < 0)
 342                 return NULL;
 343
 344         sg_miter_start(&miter, sgl, ents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);
 345
 346         lzeros = 0;
 347         len = 0;
 348         while (nbytes > 0) {
 349                 while (len && !*buff) {
 350                         lzeros++;
 351                         len--;
 352                         buff++;
 353                 }
 354
 355                 if (len && *buff)
 356                         break;
 357
 358                 sg_miter_next(&miter);
 359                 buff = miter.addr;
 360                 len = miter.length;
 361
 362                 nbytes -= lzeros;
 363                 lzeros = 0;
 364         }
 365
 366         miter.consumed = lzeros;
 367
 368         nbytes -= lzeros;
 369         nbits = nbytes * 8;
 370         if (nbits > MAX_EXTERN_MPI_BITS) {
 371                 sg_miter_stop(&miter);
 372                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 373                 return NULL;
 374         }
 375
 376         if (nbytes > 0)
 377                 nbits -= count_leading_zeros(*buff) - (BITS_PER_LONG - 8);
 378
 379         sg_miter_stop(&miter);
 380
 381         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 382         val = mpi_alloc(nlimbs);
 383         if (!val)
 384                 return NULL;
 385
 386         val->nbits = nbits;
 387         val->sign = 0;
 388         val->nlimbs = nlimbs;
 389
 390         if (nbytes == 0)
 391                 return val;
 392
 393         j = nlimbs - 1;
 394         a = 0;
 395         z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 396         z %= BYTES_PER_MPI_LIMB;
 397
 398         while (sg_miter_next(&miter)) {
 399                 buff = miter.addr;
 400                 len = miter.length;
 401
 402                 for (x = 0; x < len; x++) {
 403                         a <<= 8;
 404                         a |= *buff++;
 405                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 406                                 val->d[j--] = a;
 407                                 a = 0;
 408                         }
 409                 }
 410                 z += x;
 411         }
 412
 413         return val;
 414 }
 415 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);