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/string.h>
  25 #include "mpi-internal.h"
  26
  27 #define MAX_EXTERN_MPI_BITS 16384
  28
  29 /**
  30  * mpi_read_raw_data - Read a raw byte stream as a positive integer
  31  * @xbuffer: The data to read
  32  * @nbytes: The amount of data to read
  33  */
  34 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
  35 {
  36         const uint8_t *buffer = xbuffer;
  37         int i, j;
  38         unsigned nbits, nlimbs;
  39         mpi_limb_t a;
  40         MPI val = NULL;
  41
  42         while (nbytes > 0 && buffer[0] == 0) {
  43                 buffer++;
  44                 nbytes--;
  45         }
  46
  47         nbits = nbytes * 8;
  48         if (nbits > MAX_EXTERN_MPI_BITS) {
  49                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  50                 return NULL;
  51         }
  52         if (nbytes > 0)
  53                 nbits -= count_leading_zeros(buffer[0]) - (BITS_PER_LONG - 8);
  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         unsigned int nbits, nbytes;
  84         MPI val;
  85
  86         if (*ret_nread < 2)
  87                 return ERR_PTR(-EINVAL);
  88         nbits = buffer[0] << 8 | buffer[1];
  89
  90         if (nbits > MAX_EXTERN_MPI_BITS) {
  91                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  92                 return ERR_PTR(-EINVAL);
  93         }
  94
  95         nbytes = DIV_ROUND_UP(nbits, 8);
  96         if (nbytes + 2 > *ret_nread) {
  97                 pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
  98                                 nbytes, *ret_nread);
  99                 return ERR_PTR(-EINVAL);
 100         }
 101
 102         val = mpi_read_raw_data(buffer + 2, nbytes);
 103         if (!val)
 104                 return ERR_PTR(-ENOMEM);
 105
 106         *ret_nread = nbytes + 2;
 107         return val;
 108 }
 109 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 110
 111 static int count_lzeros(MPI a)
 112 {
 113         mpi_limb_t alimb;
 114         int i, lzeros = 0;
 115
 116         for (i = a->nlimbs - 1; i >= 0; i--) {
 117                 alimb = a->d[i];
 118                 if (alimb == 0) {
 119                         lzeros += sizeof(mpi_limb_t);
 120                 } else {
 121                         lzeros += count_leading_zeros(alimb) / 8;
 122                         break;
 123                 }
 124         }
 125         return lzeros;
 126 }
 127
 128 /**
 129  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 130  *
 131  * @a:          a multi precision integer
 132  * @buf:        bufer to which the output will be written to. Needs to be at
 133  *              leaset mpi_get_size(a) long.
 134  * @buf_len:    size of the buf.
 135  * @nbytes:     receives the actual length of the data written on success and
 136  *              the data to-be-written on -EOVERFLOW in case buf_len was too
 137  *              small.
 138  * @sign:       if not NULL, it will be set to the sign of a.
 139  *
 140  * Return:      0 on success or error code in case of error
 141  */
 142 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 143                     int *sign)
 144 {
 145         uint8_t *p;
 146 #if BYTES_PER_MPI_LIMB == 4
 147         __be32 alimb;
 148 #elif BYTES_PER_MPI_LIMB == 8
 149         __be64 alimb;
 150 #else
 151 #error please implement for this limb size.
 152 #endif
 153         unsigned int n = mpi_get_size(a);
 154         int i, lzeros;
 155
 156         if (!buf || !nbytes)
 157                 return -EINVAL;
 158
 159         if (sign)
 160                 *sign = a->sign;
 161
 162         lzeros = count_lzeros(a);
 163
 164         if (buf_len < n - lzeros) {
 165                 *nbytes = n - lzeros;
 166                 return -EOVERFLOW;
 167         }
 168
 169         p = buf;
 170         *nbytes = n - lzeros;
 171
 172         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 173                         lzeros %= BYTES_PER_MPI_LIMB;
 174                 i >= 0; i--) {
 175 #if BYTES_PER_MPI_LIMB == 4
 176                 alimb = cpu_to_be32(a->d[i]);
 177 #elif BYTES_PER_MPI_LIMB == 8
 178                 alimb = cpu_to_be64(a->d[i]);
 179 #else
 180 #error please implement for this limb size.
 181 #endif
 182                 memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
 183                 p += BYTES_PER_MPI_LIMB - lzeros;
 184                 lzeros = 0;
 185         }
 186         return 0;
 187 }
 188 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 189
 190 /*
 191  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 192  * Caller must free the return string.
 193  * This function does return a 0 byte buffer with nbytes set to zero if the
 194  * value of A is zero.
 195  *
 196  * @a:          a multi precision integer.
 197  * @nbytes:     receives the length of this buffer.
 198  * @sign:       if not NULL, it will be set to the sign of the a.
 199  *
 200  * Return:      Pointer to MPI buffer or NULL on error
 201  */
 202 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 203 {
 204         uint8_t *buf;
 205         unsigned int n;
 206         int ret;
 207
 208         if (!nbytes)
 209                 return NULL;
 210
 211         n = mpi_get_size(a);
 212
 213         if (!n)
 214                 n++;
 215
 216         buf = kmalloc(n, GFP_KERNEL);
 217
 218         if (!buf)
 219                 return NULL;
 220
 221         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 222
 223         if (ret) {
 224                 kfree(buf);
 225                 return NULL;
 226         }
 227         return buf;
 228 }
 229 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 230
 231 /**
 232  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 233  *
 234  * This function works in the same way as the mpi_read_buffer, but it
 235  * takes an sgl instead of u8 * buf.
 236  *
 237  * @a:          a multi precision integer
 238  * @sgl:        scatterlist to write to. Needs to be at least
 239  *              mpi_get_size(a) long.
 240  * @nbytes:     in/out param - it has the be set to the maximum number of
 241  *              bytes that can be written to sgl. This has to be at least
 242  *              the size of the integer a. On return it receives the actual
 243  *              length of the data written on success or the data that would
 244  *              be written if buffer was too small.
 245  * @sign:       if not NULL, it will be set to the sign of a.
 246  *
 247  * Return:      0 on success or error code in case of error
 248  */
 249 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 250                      int *sign)
 251 {
 252         u8 *p, *p2;
 253 #if BYTES_PER_MPI_LIMB == 4
 254         __be32 alimb;
 255 #elif BYTES_PER_MPI_LIMB == 8
 256         __be64 alimb;
 257 #else
 258 #error please implement for this limb size.
 259 #endif
 260         unsigned int n = mpi_get_size(a);
 261         int i, x, y = 0, lzeros, buf_len;
 262
 263         if (!nbytes)
 264                 return -EINVAL;
 265
 266         if (sign)
 267                 *sign = a->sign;
 268
 269         lzeros = count_lzeros(a);
 270
 271         if (*nbytes < n - lzeros) {
 272                 *nbytes = n - lzeros;
 273                 return -EOVERFLOW;
 274         }
 275
 276         *nbytes = n - lzeros;
 277         buf_len = sgl->length;
 278         p2 = sg_virt(sgl);
 279
 280         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 281                         lzeros %= BYTES_PER_MPI_LIMB;
 282                 i >= 0; i--) {
 283 #if BYTES_PER_MPI_LIMB == 4
 284                 alimb = cpu_to_be32(a->d[i]);
 285 #elif BYTES_PER_MPI_LIMB == 8
 286                 alimb = cpu_to_be64(a->d[i]);
 287 #else
 288 #error please implement for this limb size.
 289 #endif
 290                 if (lzeros) {
 291                         y = lzeros;
 292                         lzeros = 0;
 293                 }
 294
 295                 p = (u8 *)&alimb + y;
 296
 297                 for (x = 0; x < sizeof(alimb) - y; x++) {
 298                         if (!buf_len) {
 299                                 sgl = sg_next(sgl);
 300                                 if (!sgl)
 301                                         return -EINVAL;
 302                                 buf_len = sgl->length;
 303                                 p2 = sg_virt(sgl);
 304                         }
 305                         *p2++ = *p++;
 306                         buf_len--;
 307                 }
 308                 y = 0;
 309         }
 310         return 0;
 311 }
 312 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 313
 314 /*
 315  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 316  *                           data from the sgl
 317  *
 318  * This function works in the same way as the mpi_read_raw_data, but it
 319  * takes an sgl instead of void * buffer. i.e. it allocates
 320  * a new MPI and reads the content of the sgl to the MPI.
 321  *
 322  * @sgl:        scatterlist to read from
 323  * @nbytes:     number of bytes to read
 324  *
 325  * Return:      Pointer to a new MPI or NULL on error
 326  */
 327 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 328 {
 329         struct scatterlist *sg;
 330         int x, i, j, z, lzeros, ents;
 331         unsigned int nbits, nlimbs;
 332         mpi_limb_t a;
 333         MPI val = NULL;
 334
 335         lzeros = 0;
 336         ents = sg_nents(sgl);
 337
 338         for_each_sg(sgl, sg, ents, i) {
 339                 const u8 *buff = sg_virt(sg);
 340                 int len = sg->length;
 341
 342                 while (len && !*buff) {
 343                         lzeros++;
 344                         len--;
 345                         buff++;
 346                 }
 347
 348                 if (len && *buff)
 349                         break;
 350
 351                 ents--;
 352                 nbytes -= lzeros;
 353                 lzeros = 0;
 354         }
 355
 356         sgl = sg;
 357         nbytes -= lzeros;
 358         nbits = nbytes * 8;
 359         if (nbits > MAX_EXTERN_MPI_BITS) {
 360                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 361                 return NULL;
 362         }
 363
 364         if (nbytes > 0)
 365                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)) -
 366                         (BITS_PER_LONG - 8);
 367
 368         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 369         val = mpi_alloc(nlimbs);
 370         if (!val)
 371                 return NULL;
 372
 373         val->nbits = nbits;
 374         val->sign = 0;
 375         val->nlimbs = nlimbs;
 376
 377         if (nbytes == 0)
 378                 return val;
 379
 380         j = nlimbs - 1;
 381         a = 0;
 382         z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 383         z %= BYTES_PER_MPI_LIMB;
 384
 385         for_each_sg(sgl, sg, ents, i) {
 386                 const u8 *buffer = sg_virt(sg) + lzeros;
 387                 int len = sg->length - lzeros;
 388
 389                 for (x = 0; x < len; x++) {
 390                         a <<= 8;
 391                         a |= *buffer++;
 392                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 393                                 val->d[j--] = a;
 394                                 a = 0;
 395                         }
 396                 }
 397                 z += x;
 398                 lzeros = 0;
 399         }
 400         return val;
 401 }
 402 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);