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 "mpi-internal.h"
  24
  25 #define MAX_EXTERN_MPI_BITS 16384
  26
  27 /**
  28  * mpi_read_raw_data - Read a raw byte stream as a positive integer
  29  * @xbuffer: The data to read
  30  * @nbytes: The amount of data to read
  31  */
  32 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
  33 {
  34         const uint8_t *buffer = xbuffer;
  35         int i, j;
  36         unsigned nbits, nlimbs;
  37         mpi_limb_t a;
  38         MPI val = NULL;
  39
  40         while (nbytes > 0 && buffer[0] == 0) {
  41                 buffer++;
  42                 nbytes--;
  43         }
  44
  45         nbits = nbytes * 8;
  46         if (nbits > MAX_EXTERN_MPI_BITS) {
  47                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  48                 return NULL;
  49         }
  50         if (nbytes > 0)
  51                 nbits -= count_leading_zeros(buffer[0]);
  52         else
  53                 nbits = 0;
  54
  55         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
  56         val = mpi_alloc(nlimbs);
  57         if (!val)
  58                 return NULL;
  59         val->nbits = nbits;
  60         val->sign = 0;
  61         val->nlimbs = nlimbs;
  62
  63         if (nbytes > 0) {
  64                 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
  65                 i %= BYTES_PER_MPI_LIMB;
  66                 for (j = nlimbs; j > 0; j--) {
  67                         a = 0;
  68                         for (; i < BYTES_PER_MPI_LIMB; i++) {
  69                                 a <<= 8;
  70                                 a |= *buffer++;
  71                         }
  72                         i = 0;
  73                         val->d[j - 1] = a;
  74                 }
  75         }
  76         return val;
  77 }
  78 EXPORT_SYMBOL_GPL(mpi_read_raw_data);
  79
  80 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
  81 {
  82         const uint8_t *buffer = xbuffer;
  83         int i, j;
  84         unsigned nbits, nbytes, nlimbs, nread = 0;
  85         mpi_limb_t a;
  86         MPI val = NULL;
  87
  88         if (*ret_nread < 2)
  89                 goto leave;
  90         nbits = buffer[0] << 8 | buffer[1];
  91
  92         if (nbits > MAX_EXTERN_MPI_BITS) {
  93                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  94                 goto leave;
  95         }
  96         buffer += 2;
  97         nread = 2;
  98
  99         nbytes = DIV_ROUND_UP(nbits, 8);
 100         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 101         val = mpi_alloc(nlimbs);
 102         if (!val)
 103                 return NULL;
 104         i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 105         i %= BYTES_PER_MPI_LIMB;
 106         val->nbits = nbits;
 107         j = val->nlimbs = nlimbs;
 108         val->sign = 0;
 109         for (; j > 0; j--) {
 110                 a = 0;
 111                 for (; i < BYTES_PER_MPI_LIMB; i++) {
 112                         if (++nread > *ret_nread) {
 113                                 printk
 114                                     ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
 115                                      nread, *ret_nread);
 116                                 goto leave;
 117                         }
 118                         a <<= 8;
 119                         a |= *buffer++;
 120                 }
 121                 i = 0;
 122                 val->d[j - 1] = a;
 123         }
 124
 125 leave:
 126         *ret_nread = nread;
 127         return val;
 128 }
 129 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 130
 131 static int count_lzeros(MPI a)
 132 {
 133         mpi_limb_t alimb;
 134         int i, lzeros = 0;
 135
 136         for (i = a->nlimbs - 1; i >= 0; i--) {
 137                 alimb = a->d[i];
 138                 if (alimb == 0) {
 139                         lzeros += sizeof(mpi_limb_t);
 140                 } else {
 141                         lzeros += count_leading_zeros(alimb) / 8;
 142                         break;
 143                 }
 144         }
 145         return lzeros;
 146 }
 147
 148 /**
 149  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 150  *
 151  * @a:          a multi precision integer
 152  * @buf:        bufer to which the output will be written to. Needs to be at
 153  *              leaset mpi_get_size(a) long.
 154  * @buf_len:    size of the buf.
 155  * @nbytes:     receives the actual length of the data written on success and
 156  *              the data to-be-written on -EOVERFLOW in case buf_len was too
 157  *              small.
 158  * @sign:       if not NULL, it will be set to the sign of a.
 159  *
 160  * Return:      0 on success or error code in case of error
 161  */
 162 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 163                     int *sign)
 164 {
 165         uint8_t *p;
 166         mpi_limb_t alimb;
 167         unsigned int n = mpi_get_size(a);
 168         int i, lzeros;
 169
 170         if (!buf || !nbytes)
 171                 return -EINVAL;
 172
 173         if (sign)
 174                 *sign = a->sign;
 175
 176         lzeros = count_lzeros(a);
 177
 178         if (buf_len < n - lzeros) {
 179                 *nbytes = n - lzeros;
 180                 return -EOVERFLOW;
 181         }
 182
 183         p = buf;
 184         *nbytes = n - lzeros;
 185
 186         for (i = a->nlimbs - 1; i >= 0; i--) {
 187                 alimb = a->d[i];
 188 #if BYTES_PER_MPI_LIMB == 4
 189                 *p++ = alimb >> 24;
 190                 *p++ = alimb >> 16;
 191                 *p++ = alimb >> 8;
 192                 *p++ = alimb;
 193 #elif BYTES_PER_MPI_LIMB == 8
 194                 *p++ = alimb >> 56;
 195                 *p++ = alimb >> 48;
 196                 *p++ = alimb >> 40;
 197                 *p++ = alimb >> 32;
 198                 *p++ = alimb >> 24;
 199                 *p++ = alimb >> 16;
 200                 *p++ = alimb >> 8;
 201                 *p++ = alimb;
 202 #else
 203 #error please implement for this limb size.
 204 #endif
 205
 206                 if (lzeros > 0) {
 207                         if (lzeros >= sizeof(alimb)) {
 208                                 p -= sizeof(alimb);
 209                         } else {
 210                                 mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
 211                                 mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
 212                                                         + lzeros;
 213                                 *limb1 = *limb2;
 214                                 p -= lzeros;
 215                         }
 216                         lzeros -= sizeof(alimb);
 217                 }
 218         }
 219         return 0;
 220 }
 221 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 222
 223 /*
 224  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 225  * Caller must free the return string.
 226  * This function does return a 0 byte buffer with nbytes set to zero if the
 227  * value of A is zero.
 228  *
 229  * @a:          a multi precision integer.
 230  * @nbytes:     receives the length of this buffer.
 231  * @sign:       if not NULL, it will be set to the sign of the a.
 232  *
 233  * Return:      Pointer to MPI buffer or NULL on error
 234  */
 235 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 236 {
 237         uint8_t *buf;
 238         unsigned int n;
 239         int ret;
 240
 241         if (!nbytes)
 242                 return NULL;
 243
 244         n = mpi_get_size(a);
 245
 246         if (!n)
 247                 n++;
 248
 249         buf = kmalloc(n, GFP_KERNEL);
 250
 251         if (!buf)
 252                 return NULL;
 253
 254         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 255
 256         if (ret) {
 257                 kfree(buf);
 258                 return NULL;
 259         }
 260         return buf;
 261 }
 262 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 263
 264 /****************
 265  * Use BUFFER to update MPI.
 266  */
 267 int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
 268 {
 269         const uint8_t *buffer = xbuffer, *p;
 270         mpi_limb_t alimb;
 271         int nlimbs;
 272         int i;
 273
 274         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 275         if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
 276                 return -ENOMEM;
 277         a->sign = sign;
 278
 279         for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
 280 #if BYTES_PER_MPI_LIMB == 4
 281                 alimb = (mpi_limb_t) *p--;
 282                 alimb |= (mpi_limb_t) *p-- << 8;
 283                 alimb |= (mpi_limb_t) *p-- << 16;
 284                 alimb |= (mpi_limb_t) *p-- << 24;
 285 #elif BYTES_PER_MPI_LIMB == 8
 286                 alimb = (mpi_limb_t) *p--;
 287                 alimb |= (mpi_limb_t) *p-- << 8;
 288                 alimb |= (mpi_limb_t) *p-- << 16;
 289                 alimb |= (mpi_limb_t) *p-- << 24;
 290                 alimb |= (mpi_limb_t) *p-- << 32;
 291                 alimb |= (mpi_limb_t) *p-- << 40;
 292                 alimb |= (mpi_limb_t) *p-- << 48;
 293                 alimb |= (mpi_limb_t) *p-- << 56;
 294 #else
 295 #error please implement for this limb size.
 296 #endif
 297                 a->d[i++] = alimb;
 298         }
 299         if (p >= buffer) {
 300 #if BYTES_PER_MPI_LIMB == 4
 301                 alimb = *p--;
 302                 if (p >= buffer)
 303                         alimb |= (mpi_limb_t) *p-- << 8;
 304                 if (p >= buffer)
 305                         alimb |= (mpi_limb_t) *p-- << 16;
 306                 if (p >= buffer)
 307                         alimb |= (mpi_limb_t) *p-- << 24;
 308 #elif BYTES_PER_MPI_LIMB == 8
 309                 alimb = (mpi_limb_t) *p--;
 310                 if (p >= buffer)
 311                         alimb |= (mpi_limb_t) *p-- << 8;
 312                 if (p >= buffer)
 313                         alimb |= (mpi_limb_t) *p-- << 16;
 314                 if (p >= buffer)
 315                         alimb |= (mpi_limb_t) *p-- << 24;
 316                 if (p >= buffer)
 317                         alimb |= (mpi_limb_t) *p-- << 32;
 318                 if (p >= buffer)
 319                         alimb |= (mpi_limb_t) *p-- << 40;
 320                 if (p >= buffer)
 321                         alimb |= (mpi_limb_t) *p-- << 48;
 322                 if (p >= buffer)
 323                         alimb |= (mpi_limb_t) *p-- << 56;
 324 #else
 325 #error please implement for this limb size.
 326 #endif
 327                 a->d[i++] = alimb;
 328         }
 329         a->nlimbs = i;
 330
 331         if (i != nlimbs) {
 332                 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
 333                        nlimbs);
 334                 BUG();
 335         }
 336         return 0;
 337 }
 338 EXPORT_SYMBOL_GPL(mpi_set_buffer);
 339
 340 /**
 341  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 342  *
 343  * This function works in the same way as the mpi_read_buffer, but it
 344  * takes an sgl instead of u8 * buf.
 345  *
 346  * @a:          a multi precision integer
 347  * @sgl:        scatterlist to write to. Needs to be at least
 348  *              mpi_get_size(a) long.
 349  * @nbytes:     in/out param - it has the be set to the maximum number of
 350  *              bytes that can be written to sgl. This has to be at least
 351  *              the size of the integer a. On return it receives the actual
 352  *              length of the data written on success or the data that would
 353  *              be written if buffer was too small.
 354  * @sign:       if not NULL, it will be set to the sign of a.
 355  *
 356  * Return:      0 on success or error code in case of error
 357  */
 358 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 359                      int *sign)
 360 {
 361         u8 *p, *p2;
 362         mpi_limb_t alimb, alimb2;
 363         unsigned int n = mpi_get_size(a);
 364         int i, x, y = 0, lzeros, buf_len;
 365
 366         if (!nbytes)
 367                 return -EINVAL;
 368
 369         if (sign)
 370                 *sign = a->sign;
 371
 372         lzeros = count_lzeros(a);
 373
 374         if (*nbytes < n - lzeros) {
 375                 *nbytes = n - lzeros;
 376                 return -EOVERFLOW;
 377         }
 378
 379         *nbytes = n - lzeros;
 380         buf_len = sgl->length;
 381         p2 = sg_virt(sgl);
 382
 383         for (i = a->nlimbs - 1; i >= 0; i--) {
 384                 alimb = a->d[i];
 385                 p = (u8 *)&alimb2;
 386 #if BYTES_PER_MPI_LIMB == 4
 387                 *p++ = alimb >> 24;
 388                 *p++ = alimb >> 16;
 389                 *p++ = alimb >> 8;
 390                 *p++ = alimb;
 391 #elif BYTES_PER_MPI_LIMB == 8
 392                 *p++ = alimb >> 56;
 393                 *p++ = alimb >> 48;
 394                 *p++ = alimb >> 40;
 395                 *p++ = alimb >> 32;
 396                 *p++ = alimb >> 24;
 397                 *p++ = alimb >> 16;
 398                 *p++ = alimb >> 8;
 399                 *p++ = alimb;
 400 #else
 401 #error please implement for this limb size.
 402 #endif
 403                 if (lzeros > 0) {
 404                         if (lzeros >= sizeof(alimb)) {
 405                                 p -= sizeof(alimb);
 406                                 continue;
 407                         } else {
 408                                 mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
 409                                 mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
 410                                                         + lzeros;
 411                                 *limb1 = *limb2;
 412                                 p -= lzeros;
 413                                 y = lzeros;
 414                         }
 415                         lzeros -= sizeof(alimb);
 416                 }
 417
 418                 p = p - (sizeof(alimb) - y);
 419
 420                 for (x = 0; x < sizeof(alimb) - y; x++) {
 421                         if (!buf_len) {
 422                                 sgl = sg_next(sgl);
 423                                 if (!sgl)
 424                                         return -EINVAL;
 425                                 buf_len = sgl->length;
 426                                 p2 = sg_virt(sgl);
 427                         }
 428                         *p2++ = *p++;
 429                         buf_len--;
 430                 }
 431                 y = 0;
 432         }
 433         return 0;
 434 }
 435 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 436
 437 /*
 438  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 439  *                           data from the sgl
 440  *
 441  * This function works in the same way as the mpi_read_raw_data, but it
 442  * takes an sgl instead of void * buffer. i.e. it allocates
 443  * a new MPI and reads the content of the sgl to the MPI.
 444  *
 445  * @sgl:        scatterlist to read from
 446  * @len:        number of bytes to read
 447  *
 448  * Return:      Pointer to a new MPI or NULL on error
 449  */
 450 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int len)
 451 {
 452         struct scatterlist *sg;
 453         int x, i, j, z, lzeros, ents;
 454         unsigned int nbits, nlimbs, nbytes;
 455         mpi_limb_t a;
 456         MPI val = NULL;
 457
 458         lzeros = 0;
 459         ents = sg_nents(sgl);
 460
 461         for_each_sg(sgl, sg, ents, i) {
 462                 const u8 *buff = sg_virt(sg);
 463                 int len = sg->length;
 464
 465                 while (len && !*buff) {
 466                         lzeros++;
 467                         len--;
 468                         buff++;
 469                 }
 470
 471                 if (len && *buff)
 472                         break;
 473
 474                 ents--;
 475                 lzeros = 0;
 476         }
 477
 478         sgl = sg;
 479
 480         if (!ents)
 481                 nbytes = 0;
 482         else
 483                 nbytes = len - lzeros;
 484
 485         nbits = nbytes * 8;
 486         if (nbits > MAX_EXTERN_MPI_BITS) {
 487                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 488                 return NULL;
 489         }
 490
 491         if (nbytes > 0)
 492                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
 493         else
 494                 nbits = 0;
 495
 496         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 497         val = mpi_alloc(nlimbs);
 498         if (!val)
 499                 return NULL;
 500
 501         val->nbits = nbits;
 502         val->sign = 0;
 503         val->nlimbs = nlimbs;
 504
 505         if (nbytes == 0)
 506                 return val;
 507
 508         j = nlimbs - 1;
 509         a = 0;
 510         z = 0;
 511         x = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 512         x %= BYTES_PER_MPI_LIMB;
 513
 514         for_each_sg(sgl, sg, ents, i) {
 515                 const u8 *buffer = sg_virt(sg) + lzeros;
 516                 int len = sg->length - lzeros;
 517                 int buf_shift = x;
 518
 519                 if  (sg_is_last(sg) && (len % BYTES_PER_MPI_LIMB))
 520                         len += BYTES_PER_MPI_LIMB - (len % BYTES_PER_MPI_LIMB);
 521
 522                 for (; x < len + buf_shift; x++) {
 523                         a <<= 8;
 524                         a |= *buffer++;
 525                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 526                                 val->d[j--] = a;
 527                                 a = 0;
 528                         }
 529                 }
 530                 z += x;
 531                 x = 0;
 532                 lzeros = 0;
 533         }
 534         return val;
 535 }
 536 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);