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 "mpi-internal.h"
  25
  26 #define MAX_EXTERN_MPI_BITS 16384
  27
  28 /**
  29  * mpi_read_raw_data - Read a raw byte stream as a positive integer
  30  * @xbuffer: The data to read
  31  * @nbytes: The amount of data to read
  32  */
  33 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
  34 {
  35         const uint8_t *buffer = xbuffer;
  36         int i, j;
  37         unsigned nbits, nlimbs;
  38         mpi_limb_t a;
  39         MPI val = NULL;
  40
  41         while (nbytes > 0 && buffer[0] == 0) {
  42                 buffer++;
  43                 nbytes--;
  44         }
  45
  46         nbits = nbytes * 8;
  47         if (nbits > MAX_EXTERN_MPI_BITS) {
  48                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  49                 return NULL;
  50         }
  51         if (nbytes > 0)
  52                 nbits -= count_leading_zeros(buffer[0]);
  53         else
  54                 nbits = 0;
  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         int i, j;
  85         unsigned nbits, nbytes, nlimbs, nread = 0;
  86         mpi_limb_t a;
  87         MPI val = NULL;
  88
  89         if (*ret_nread < 2)
  90                 goto leave;
  91         nbits = buffer[0] << 8 | buffer[1];
  92
  93         if (nbits > MAX_EXTERN_MPI_BITS) {
  94                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  95                 goto leave;
  96         }
  97         buffer += 2;
  98         nread = 2;
  99
 100         nbytes = DIV_ROUND_UP(nbits, 8);
 101         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 102         val = mpi_alloc(nlimbs);
 103         if (!val)
 104                 return NULL;
 105         i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 106         i %= BYTES_PER_MPI_LIMB;
 107         val->nbits = nbits;
 108         j = val->nlimbs = nlimbs;
 109         val->sign = 0;
 110         for (; j > 0; j--) {
 111                 a = 0;
 112                 for (; i < BYTES_PER_MPI_LIMB; i++) {
 113                         if (++nread > *ret_nread) {
 114                                 printk
 115                                     ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
 116                                      nread, *ret_nread);
 117                                 goto leave;
 118                         }
 119                         a <<= 8;
 120                         a |= *buffer++;
 121                 }
 122                 i = 0;
 123                 val->d[j - 1] = a;
 124         }
 125
 126 leave:
 127         *ret_nread = nread;
 128         return val;
 129 }
 130 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 131
 132 static int count_lzeros(MPI a)
 133 {
 134         mpi_limb_t alimb;
 135         int i, lzeros = 0;
 136
 137         for (i = a->nlimbs - 1; i >= 0; i--) {
 138                 alimb = a->d[i];
 139                 if (alimb == 0) {
 140                         lzeros += sizeof(mpi_limb_t);
 141                 } else {
 142                         lzeros += count_leading_zeros(alimb) / 8;
 143                         break;
 144                 }
 145         }
 146         return lzeros;
 147 }
 148
 149 /**
 150  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 151  *
 152  * @a:          a multi precision integer
 153  * @buf:        bufer to which the output will be written to. Needs to be at
 154  *              leaset mpi_get_size(a) long.
 155  * @buf_len:    size of the buf.
 156  * @nbytes:     receives the actual length of the data written on success and
 157  *              the data to-be-written on -EOVERFLOW in case buf_len was too
 158  *              small.
 159  * @sign:       if not NULL, it will be set to the sign of a.
 160  *
 161  * Return:      0 on success or error code in case of error
 162  */
 163 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 164                     int *sign)
 165 {
 166         uint8_t *p;
 167         mpi_limb_t alimb;
 168         unsigned int n = mpi_get_size(a);
 169         int i, lzeros;
 170
 171         if (!buf || !nbytes)
 172                 return -EINVAL;
 173
 174         if (sign)
 175                 *sign = a->sign;
 176
 177         lzeros = count_lzeros(a);
 178
 179         if (buf_len < n - lzeros) {
 180                 *nbytes = n - lzeros;
 181                 return -EOVERFLOW;
 182         }
 183
 184         p = buf;
 185         *nbytes = n - lzeros;
 186
 187         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 188                         lzeros %= BYTES_PER_MPI_LIMB;
 189                 i >= 0; i--) {
 190                 alimb = a->d[i];
 191 #if BYTES_PER_MPI_LIMB == 4
 192                 *p++ = alimb >> 24;
 193                 *p++ = alimb >> 16;
 194                 *p++ = alimb >> 8;
 195                 *p++ = alimb;
 196 #elif BYTES_PER_MPI_LIMB == 8
 197                 *p++ = alimb >> 56;
 198                 *p++ = alimb >> 48;
 199                 *p++ = alimb >> 40;
 200                 *p++ = alimb >> 32;
 201                 *p++ = alimb >> 24;
 202                 *p++ = alimb >> 16;
 203                 *p++ = alimb >> 8;
 204                 *p++ = alimb;
 205 #else
 206 #error please implement for this limb size.
 207 #endif
 208
 209                 if (lzeros > 0) {
 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                         lzeros -= sizeof(alimb);
 216                 }
 217         }
 218         return 0;
 219 }
 220 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 221
 222 /*
 223  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 224  * Caller must free the return string.
 225  * This function does return a 0 byte buffer with nbytes set to zero if the
 226  * value of A is zero.
 227  *
 228  * @a:          a multi precision integer.
 229  * @nbytes:     receives the length of this buffer.
 230  * @sign:       if not NULL, it will be set to the sign of the a.
 231  *
 232  * Return:      Pointer to MPI buffer or NULL on error
 233  */
 234 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 235 {
 236         uint8_t *buf;
 237         unsigned int n;
 238         int ret;
 239
 240         if (!nbytes)
 241                 return NULL;
 242
 243         n = mpi_get_size(a);
 244
 245         if (!n)
 246                 n++;
 247
 248         buf = kmalloc(n, GFP_KERNEL);
 249
 250         if (!buf)
 251                 return NULL;
 252
 253         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 254
 255         if (ret) {
 256                 kfree(buf);
 257                 return NULL;
 258         }
 259         return buf;
 260 }
 261 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 262
 263 /****************
 264  * Use BUFFER to update MPI.
 265  */
 266 int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
 267 {
 268         const uint8_t *buffer = xbuffer, *p;
 269         mpi_limb_t alimb;
 270         int nlimbs;
 271         int i;
 272
 273         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 274         if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
 275                 return -ENOMEM;
 276         a->sign = sign;
 277
 278         for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
 279 #if BYTES_PER_MPI_LIMB == 4
 280                 alimb = (mpi_limb_t) *p--;
 281                 alimb |= (mpi_limb_t) *p-- << 8;
 282                 alimb |= (mpi_limb_t) *p-- << 16;
 283                 alimb |= (mpi_limb_t) *p-- << 24;
 284 #elif BYTES_PER_MPI_LIMB == 8
 285                 alimb = (mpi_limb_t) *p--;
 286                 alimb |= (mpi_limb_t) *p-- << 8;
 287                 alimb |= (mpi_limb_t) *p-- << 16;
 288                 alimb |= (mpi_limb_t) *p-- << 24;
 289                 alimb |= (mpi_limb_t) *p-- << 32;
 290                 alimb |= (mpi_limb_t) *p-- << 40;
 291                 alimb |= (mpi_limb_t) *p-- << 48;
 292                 alimb |= (mpi_limb_t) *p-- << 56;
 293 #else
 294 #error please implement for this limb size.
 295 #endif
 296                 a->d[i++] = alimb;
 297         }
 298         if (p >= buffer) {
 299 #if BYTES_PER_MPI_LIMB == 4
 300                 alimb = *p--;
 301                 if (p >= buffer)
 302                         alimb |= (mpi_limb_t) *p-- << 8;
 303                 if (p >= buffer)
 304                         alimb |= (mpi_limb_t) *p-- << 16;
 305                 if (p >= buffer)
 306                         alimb |= (mpi_limb_t) *p-- << 24;
 307 #elif BYTES_PER_MPI_LIMB == 8
 308                 alimb = (mpi_limb_t) *p--;
 309                 if (p >= buffer)
 310                         alimb |= (mpi_limb_t) *p-- << 8;
 311                 if (p >= buffer)
 312                         alimb |= (mpi_limb_t) *p-- << 16;
 313                 if (p >= buffer)
 314                         alimb |= (mpi_limb_t) *p-- << 24;
 315                 if (p >= buffer)
 316                         alimb |= (mpi_limb_t) *p-- << 32;
 317                 if (p >= buffer)
 318                         alimb |= (mpi_limb_t) *p-- << 40;
 319                 if (p >= buffer)
 320                         alimb |= (mpi_limb_t) *p-- << 48;
 321                 if (p >= buffer)
 322                         alimb |= (mpi_limb_t) *p-- << 56;
 323 #else
 324 #error please implement for this limb size.
 325 #endif
 326                 a->d[i++] = alimb;
 327         }
 328         a->nlimbs = i;
 329
 330         if (i != nlimbs) {
 331                 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
 332                        nlimbs);
 333                 BUG();
 334         }
 335         return 0;
 336 }
 337 EXPORT_SYMBOL_GPL(mpi_set_buffer);
 338
 339 /**
 340  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 341  *
 342  * This function works in the same way as the mpi_read_buffer, but it
 343  * takes an sgl instead of u8 * buf.
 344  *
 345  * @a:          a multi precision integer
 346  * @sgl:        scatterlist to write to. Needs to be at least
 347  *              mpi_get_size(a) long.
 348  * @nbytes:     in/out param - it has the be set to the maximum number of
 349  *              bytes that can be written to sgl. This has to be at least
 350  *              the size of the integer a. On return it receives the actual
 351  *              length of the data written on success or the data that would
 352  *              be written if buffer was too small.
 353  * @sign:       if not NULL, it will be set to the sign of a.
 354  *
 355  * Return:      0 on success or error code in case of error
 356  */
 357 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 358                      int *sign)
 359 {
 360         u8 *p, *p2;
 361 #if BYTES_PER_MPI_LIMB == 4
 362         __be32 alimb;
 363 #elif BYTES_PER_MPI_LIMB == 8
 364         __be64 alimb;
 365 #else
 366 #error please implement for this limb size.
 367 #endif
 368         unsigned int n = mpi_get_size(a);
 369         int i, x, y = 0, lzeros, buf_len;
 370
 371         if (!nbytes)
 372                 return -EINVAL;
 373
 374         if (sign)
 375                 *sign = a->sign;
 376
 377         lzeros = count_lzeros(a);
 378
 379         if (*nbytes < n - lzeros) {
 380                 *nbytes = n - lzeros;
 381                 return -EOVERFLOW;
 382         }
 383
 384         *nbytes = n - lzeros;
 385         buf_len = sgl->length;
 386         p2 = sg_virt(sgl);
 387
 388         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 389                         lzeros %= BYTES_PER_MPI_LIMB;
 390                 i >= 0; i--) {
 391 #if BYTES_PER_MPI_LIMB == 4
 392                 alimb = cpu_to_be32(a->d[i]);
 393 #elif BYTES_PER_MPI_LIMB == 8
 394                 alimb = cpu_to_be64(a->d[i]);
 395 #else
 396 #error please implement for this limb size.
 397 #endif
 398                 if (lzeros) {
 399                         y = lzeros;
 400                         lzeros = 0;
 401                 }
 402
 403                 p = (u8 *)&alimb + y;
 404
 405                 for (x = 0; x < sizeof(alimb) - y; x++) {
 406                         if (!buf_len) {
 407                                 sgl = sg_next(sgl);
 408                                 if (!sgl)
 409                                         return -EINVAL;
 410                                 buf_len = sgl->length;
 411                                 p2 = sg_virt(sgl);
 412                         }
 413                         *p2++ = *p++;
 414                         buf_len--;
 415                 }
 416                 y = 0;
 417         }
 418         return 0;
 419 }
 420 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 421
 422 /*
 423  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 424  *                           data from the sgl
 425  *
 426  * This function works in the same way as the mpi_read_raw_data, but it
 427  * takes an sgl instead of void * buffer. i.e. it allocates
 428  * a new MPI and reads the content of the sgl to the MPI.
 429  *
 430  * @sgl:        scatterlist to read from
 431  * @len:        number of bytes to read
 432  *
 433  * Return:      Pointer to a new MPI or NULL on error
 434  */
 435 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int len)
 436 {
 437         struct scatterlist *sg;
 438         int x, i, j, z, lzeros, ents;
 439         unsigned int nbits, nlimbs, nbytes;
 440         mpi_limb_t a;
 441         MPI val = NULL;
 442
 443         lzeros = 0;
 444         ents = sg_nents(sgl);
 445
 446         for_each_sg(sgl, sg, ents, i) {
 447                 const u8 *buff = sg_virt(sg);
 448                 int len = sg->length;
 449
 450                 while (len && !*buff) {
 451                         lzeros++;
 452                         len--;
 453                         buff++;
 454                 }
 455
 456                 if (len && *buff)
 457                         break;
 458
 459                 ents--;
 460                 lzeros = 0;
 461         }
 462
 463         sgl = sg;
 464
 465         if (!ents)
 466                 nbytes = 0;
 467         else
 468                 nbytes = len - lzeros;
 469
 470         nbits = nbytes * 8;
 471         if (nbits > MAX_EXTERN_MPI_BITS) {
 472                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 473                 return NULL;
 474         }
 475
 476         if (nbytes > 0)
 477                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
 478         else
 479                 nbits = 0;
 480
 481         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 482         val = mpi_alloc(nlimbs);
 483         if (!val)
 484                 return NULL;
 485
 486         val->nbits = nbits;
 487         val->sign = 0;
 488         val->nlimbs = nlimbs;
 489
 490         if (nbytes == 0)
 491                 return val;
 492
 493         j = nlimbs - 1;
 494         a = 0;
 495         z = 0;
 496         x = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 497         x %= BYTES_PER_MPI_LIMB;
 498
 499         for_each_sg(sgl, sg, ents, i) {
 500                 const u8 *buffer = sg_virt(sg) + lzeros;
 501                 int len = sg->length - lzeros;
 502                 int buf_shift = x;
 503
 504                 if  (sg_is_last(sg) && (len % BYTES_PER_MPI_LIMB))
 505                         len += BYTES_PER_MPI_LIMB - (len % BYTES_PER_MPI_LIMB);
 506
 507                 for (; x < len + buf_shift; x++) {
 508                         a <<= 8;
 509                         a |= *buffer++;
 510                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 511                                 val->d[j--] = a;
 512                                 a = 0;
 513                         }
 514                 }
 515                 z += x;
 516                 x = 0;
 517                 lzeros = 0;
 518         }
 519         return val;
 520 }
 521 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);