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.
 156  * @sign:       if not NULL, it will be set to the sign of a.
 157  *
 158  * Return:      0 on success or error code in case of error
 159  */
 160 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 161                     int *sign)
 162 {
 163         uint8_t *p;
 164         mpi_limb_t alimb;
 165         unsigned int n = mpi_get_size(a);
 166         int i, lzeros;
 167
 168         if (buf_len < n || !buf || !nbytes)
 169                 return -EINVAL;
 170
 171         if (sign)
 172                 *sign = a->sign;
 173
 174         lzeros = count_lzeros(a);
 175
 176         p = buf;
 177         *nbytes = n - lzeros;
 178
 179         for (i = a->nlimbs - 1; i >= 0; i--) {
 180                 alimb = a->d[i];
 181 #if BYTES_PER_MPI_LIMB == 4
 182                 *p++ = alimb >> 24;
 183                 *p++ = alimb >> 16;
 184                 *p++ = alimb >> 8;
 185                 *p++ = alimb;
 186 #elif BYTES_PER_MPI_LIMB == 8
 187                 *p++ = alimb >> 56;
 188                 *p++ = alimb >> 48;
 189                 *p++ = alimb >> 40;
 190                 *p++ = alimb >> 32;
 191                 *p++ = alimb >> 24;
 192                 *p++ = alimb >> 16;
 193                 *p++ = alimb >> 8;
 194                 *p++ = alimb;
 195 #else
 196 #error please implement for this limb size.
 197 #endif
 198
 199                 if (lzeros > 0) {
 200                         if (lzeros >= sizeof(alimb)) {
 201                                 p -= sizeof(alimb);
 202                         } else {
 203                                 mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
 204                                 mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
 205                                                         + lzeros;
 206                                 *limb1 = *limb2;
 207                                 p -= lzeros;
 208                         }
 209                         lzeros -= sizeof(alimb);
 210                 }
 211         }
 212         return 0;
 213 }
 214 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 215
 216 /*
 217  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 218  * Caller must free the return string.
 219  * This function does return a 0 byte buffer with nbytes set to zero if the
 220  * value of A is zero.
 221  *
 222  * @a:          a multi precision integer.
 223  * @nbytes:     receives the length of this buffer.
 224  * @sign:       if not NULL, it will be set to the sign of the a.
 225  *
 226  * Return:      Pointer to MPI buffer or NULL on error
 227  */
 228 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 229 {
 230         uint8_t *buf;
 231         unsigned int n;
 232         int ret;
 233
 234         if (!nbytes)
 235                 return NULL;
 236
 237         n = mpi_get_size(a);
 238
 239         if (!n)
 240                 n++;
 241
 242         buf = kmalloc(n, GFP_KERNEL);
 243
 244         if (!buf)
 245                 return NULL;
 246
 247         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 248
 249         if (ret) {
 250                 kfree(buf);
 251                 return NULL;
 252         }
 253         return buf;
 254 }
 255 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 256
 257 /****************
 258  * Use BUFFER to update MPI.
 259  */
 260 int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
 261 {
 262         const uint8_t *buffer = xbuffer, *p;
 263         mpi_limb_t alimb;
 264         int nlimbs;
 265         int i;
 266
 267         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 268         if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
 269                 return -ENOMEM;
 270         a->sign = sign;
 271
 272         for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
 273 #if BYTES_PER_MPI_LIMB == 4
 274                 alimb = (mpi_limb_t) *p--;
 275                 alimb |= (mpi_limb_t) *p-- << 8;
 276                 alimb |= (mpi_limb_t) *p-- << 16;
 277                 alimb |= (mpi_limb_t) *p-- << 24;
 278 #elif BYTES_PER_MPI_LIMB == 8
 279                 alimb = (mpi_limb_t) *p--;
 280                 alimb |= (mpi_limb_t) *p-- << 8;
 281                 alimb |= (mpi_limb_t) *p-- << 16;
 282                 alimb |= (mpi_limb_t) *p-- << 24;
 283                 alimb |= (mpi_limb_t) *p-- << 32;
 284                 alimb |= (mpi_limb_t) *p-- << 40;
 285                 alimb |= (mpi_limb_t) *p-- << 48;
 286                 alimb |= (mpi_limb_t) *p-- << 56;
 287 #else
 288 #error please implement for this limb size.
 289 #endif
 290                 a->d[i++] = alimb;
 291         }
 292         if (p >= buffer) {
 293 #if BYTES_PER_MPI_LIMB == 4
 294                 alimb = *p--;
 295                 if (p >= buffer)
 296                         alimb |= (mpi_limb_t) *p-- << 8;
 297                 if (p >= buffer)
 298                         alimb |= (mpi_limb_t) *p-- << 16;
 299                 if (p >= buffer)
 300                         alimb |= (mpi_limb_t) *p-- << 24;
 301 #elif BYTES_PER_MPI_LIMB == 8
 302                 alimb = (mpi_limb_t) *p--;
 303                 if (p >= buffer)
 304                         alimb |= (mpi_limb_t) *p-- << 8;
 305                 if (p >= buffer)
 306                         alimb |= (mpi_limb_t) *p-- << 16;
 307                 if (p >= buffer)
 308                         alimb |= (mpi_limb_t) *p-- << 24;
 309                 if (p >= buffer)
 310                         alimb |= (mpi_limb_t) *p-- << 32;
 311                 if (p >= buffer)
 312                         alimb |= (mpi_limb_t) *p-- << 40;
 313                 if (p >= buffer)
 314                         alimb |= (mpi_limb_t) *p-- << 48;
 315                 if (p >= buffer)
 316                         alimb |= (mpi_limb_t) *p-- << 56;
 317 #else
 318 #error please implement for this limb size.
 319 #endif
 320                 a->d[i++] = alimb;
 321         }
 322         a->nlimbs = i;
 323
 324         if (i != nlimbs) {
 325                 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
 326                        nlimbs);
 327                 BUG();
 328         }
 329         return 0;
 330 }
 331 EXPORT_SYMBOL_GPL(mpi_set_buffer);
 332
 333 /**
 334  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 335  *
 336  * This function works in the same way as the mpi_read_buffer, but it
 337  * takes an sgl instead of u8 * buf.
 338  *
 339  * @a:          a multi precision integer
 340  * @sgl:        scatterlist to write to. Needs to be at least
 341  *              mpi_get_size(a) long.
 342  * @nbytes:     in/out param - it has the be set to the maximum number of
 343  *              bytes that can be written to sgl. This has to be at least
 344  *              the size of the integer a. On return it receives the actual
 345  *              length of the data written.
 346  * @sign:       if not NULL, it will be set to the sign of a.
 347  *
 348  * Return:      0 on success or error code in case of error
 349  */
 350 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 351                      int *sign)
 352 {
 353         u8 *p, *p2;
 354         mpi_limb_t alimb, alimb2;
 355         unsigned int n = mpi_get_size(a);
 356         int i, x, y = 0, lzeros, buf_len;
 357
 358         if (!nbytes || *nbytes < n)
 359                 return -EINVAL;
 360
 361         if (sign)
 362                 *sign = a->sign;
 363
 364         lzeros = count_lzeros(a);
 365
 366         *nbytes = n - lzeros;
 367         buf_len = sgl->length;
 368         p2 = sg_virt(sgl);
 369
 370         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 371                         lzeros %= BYTES_PER_MPI_LIMB;
 372                 i >= 0; i--) {
 373                 alimb = a->d[i];
 374                 p = (u8 *)&alimb2;
 375 #if BYTES_PER_MPI_LIMB == 4
 376                 *p++ = alimb >> 24;
 377                 *p++ = alimb >> 16;
 378                 *p++ = alimb >> 8;
 379                 *p++ = alimb;
 380 #elif BYTES_PER_MPI_LIMB == 8
 381                 *p++ = alimb >> 56;
 382                 *p++ = alimb >> 48;
 383                 *p++ = alimb >> 40;
 384                 *p++ = alimb >> 32;
 385                 *p++ = alimb >> 24;
 386                 *p++ = alimb >> 16;
 387                 *p++ = alimb >> 8;
 388                 *p++ = alimb;
 389 #else
 390 #error please implement for this limb size.
 391 #endif
 392                 if (lzeros > 0) {
 393                         mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
 394                         mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
 395                                 + lzeros;
 396                         *limb1 = *limb2;
 397                         p -= lzeros;
 398                         y = lzeros;
 399                         lzeros -= sizeof(alimb);
 400                 }
 401
 402                 p = p - (sizeof(alimb) - y);
 403
 404                 for (x = 0; x < sizeof(alimb) - y; x++) {
 405                         if (!buf_len) {
 406                                 sgl = sg_next(sgl);
 407                                 if (!sgl)
 408                                         return -EINVAL;
 409                                 buf_len = sgl->length;
 410                                 p2 = sg_virt(sgl);
 411                         }
 412                         *p2++ = *p++;
 413                         buf_len--;
 414                 }
 415                 y = 0;
 416         }
 417         return 0;
 418 }
 419 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 420
 421 /*
 422  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 423  *                           data from the sgl
 424  *
 425  * This function works in the same way as the mpi_read_raw_data, but it
 426  * takes an sgl instead of void * buffer. i.e. it allocates
 427  * a new MPI and reads the content of the sgl to the MPI.
 428  *
 429  * @sgl:        scatterlist to read from
 430  * @len:        number of bytes to read
 431  *
 432  * Return:      Pointer to a new MPI or NULL on error
 433  */
 434 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int len)
 435 {
 436         struct scatterlist *sg;
 437         int x, i, j, z, lzeros, ents;
 438         unsigned int nbits, nlimbs, nbytes;
 439         mpi_limb_t a;
 440         MPI val = NULL;
 441
 442         lzeros = 0;
 443         ents = sg_nents(sgl);
 444
 445         for_each_sg(sgl, sg, ents, i) {
 446                 const u8 *buff = sg_virt(sg);
 447                 int len = sg->length;
 448
 449                 while (len && !*buff) {
 450                         lzeros++;
 451                         len--;
 452                         buff++;
 453                 }
 454
 455                 if (len && *buff)
 456                         break;
 457
 458                 ents--;
 459                 lzeros = 0;
 460         }
 461
 462         sgl = sg;
 463
 464         if (!ents)
 465                 nbytes = 0;
 466         else
 467                 nbytes = len - lzeros;
 468
 469         nbits = nbytes * 8;
 470         if (nbits > MAX_EXTERN_MPI_BITS) {
 471                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 472                 return NULL;
 473         }
 474
 475         if (nbytes > 0)
 476                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
 477         else
 478                 nbits = 0;
 479
 480         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 481         val = mpi_alloc(nlimbs);
 482         if (!val)
 483                 return NULL;
 484
 485         val->nbits = nbits;
 486         val->sign = 0;
 487         val->nlimbs = nlimbs;
 488
 489         if (nbytes == 0)
 490                 return val;
 491
 492         j = nlimbs - 1;
 493         a = 0;
 494         z = 0;
 495         x = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 496         x %= BYTES_PER_MPI_LIMB;
 497
 498         for_each_sg(sgl, sg, ents, i) {
 499                 const u8 *buffer = sg_virt(sg) + lzeros;
 500                 int len = sg->length - lzeros;
 501                 int buf_shift = x;
 502
 503                 if  (sg_is_last(sg) && (len % BYTES_PER_MPI_LIMB))
 504                         len += BYTES_PER_MPI_LIMB - (len % BYTES_PER_MPI_LIMB);
 505
 506                 for (; x < len + buf_shift; x++) {
 507                         a <<= 8;
 508                         a |= *buffer++;
 509                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 510                                 val->d[j--] = a;
 511                                 a = 0;
 512                         }
 513                 }
 514                 z += x;
 515                 x = 0;
 516                 lzeros = 0;
 517         }
 518         return val;
 519 }
 520 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);