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         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                 return ERR_PTR(-EINVAL);
  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                 return ERR_PTR(-EINVAL);
  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 ERR_PTR(-ENOMEM);
 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 #if BYTES_PER_MPI_LIMB == 4
 167         __be32 alimb;
 168 #elif BYTES_PER_MPI_LIMB == 8
 169         __be64 alimb;
 170 #else
 171 #error please implement for this limb size.
 172 #endif
 173         unsigned int n = mpi_get_size(a);
 174         int i, lzeros;
 175
 176         if (!buf || !nbytes)
 177                 return -EINVAL;
 178
 179         if (sign)
 180                 *sign = a->sign;
 181
 182         lzeros = count_lzeros(a);
 183
 184         if (buf_len < n - lzeros) {
 185                 *nbytes = n - lzeros;
 186                 return -EOVERFLOW;
 187         }
 188
 189         p = buf;
 190         *nbytes = n - lzeros;
 191
 192         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 193                         lzeros %= BYTES_PER_MPI_LIMB;
 194                 i >= 0; i--) {
 195 #if BYTES_PER_MPI_LIMB == 4
 196                 alimb = cpu_to_be32(a->d[i]);
 197 #elif BYTES_PER_MPI_LIMB == 8
 198                 alimb = cpu_to_be64(a->d[i]);
 199 #else
 200 #error please implement for this limb size.
 201 #endif
 202                 memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
 203                 p += BYTES_PER_MPI_LIMB - lzeros;
 204                 lzeros = 0;
 205         }
 206         return 0;
 207 }
 208 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 209
 210 /*
 211  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 212  * Caller must free the return string.
 213  * This function does return a 0 byte buffer with nbytes set to zero if the
 214  * value of A is zero.
 215  *
 216  * @a:          a multi precision integer.
 217  * @nbytes:     receives the length of this buffer.
 218  * @sign:       if not NULL, it will be set to the sign of the a.
 219  *
 220  * Return:      Pointer to MPI buffer or NULL on error
 221  */
 222 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 223 {
 224         uint8_t *buf;
 225         unsigned int n;
 226         int ret;
 227
 228         if (!nbytes)
 229                 return NULL;
 230
 231         n = mpi_get_size(a);
 232
 233         if (!n)
 234                 n++;
 235
 236         buf = kmalloc(n, GFP_KERNEL);
 237
 238         if (!buf)
 239                 return NULL;
 240
 241         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 242
 243         if (ret) {
 244                 kfree(buf);
 245                 return NULL;
 246         }
 247         return buf;
 248 }
 249 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 250
 251 /**
 252  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 253  *
 254  * This function works in the same way as the mpi_read_buffer, but it
 255  * takes an sgl instead of u8 * buf.
 256  *
 257  * @a:          a multi precision integer
 258  * @sgl:        scatterlist to write to. Needs to be at least
 259  *              mpi_get_size(a) long.
 260  * @nbytes:     in/out param - it has the be set to the maximum number of
 261  *              bytes that can be written to sgl. This has to be at least
 262  *              the size of the integer a. On return it receives the actual
 263  *              length of the data written on success or the data that would
 264  *              be written if buffer was too small.
 265  * @sign:       if not NULL, it will be set to the sign of a.
 266  *
 267  * Return:      0 on success or error code in case of error
 268  */
 269 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 270                      int *sign)
 271 {
 272         u8 *p, *p2;
 273 #if BYTES_PER_MPI_LIMB == 4
 274         __be32 alimb;
 275 #elif BYTES_PER_MPI_LIMB == 8
 276         __be64 alimb;
 277 #else
 278 #error please implement for this limb size.
 279 #endif
 280         unsigned int n = mpi_get_size(a);
 281         int i, x, y = 0, lzeros, buf_len;
 282
 283         if (!nbytes)
 284                 return -EINVAL;
 285
 286         if (sign)
 287                 *sign = a->sign;
 288
 289         lzeros = count_lzeros(a);
 290
 291         if (*nbytes < n - lzeros) {
 292                 *nbytes = n - lzeros;
 293                 return -EOVERFLOW;
 294         }
 295
 296         *nbytes = n - lzeros;
 297         buf_len = sgl->length;
 298         p2 = sg_virt(sgl);
 299
 300         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 301                         lzeros %= BYTES_PER_MPI_LIMB;
 302                 i >= 0; i--) {
 303 #if BYTES_PER_MPI_LIMB == 4
 304                 alimb = cpu_to_be32(a->d[i]);
 305 #elif BYTES_PER_MPI_LIMB == 8
 306                 alimb = cpu_to_be64(a->d[i]);
 307 #else
 308 #error please implement for this limb size.
 309 #endif
 310                 if (lzeros) {
 311                         y = lzeros;
 312                         lzeros = 0;
 313                 }
 314
 315                 p = (u8 *)&alimb + y;
 316
 317                 for (x = 0; x < sizeof(alimb) - y; x++) {
 318                         if (!buf_len) {
 319                                 sgl = sg_next(sgl);
 320                                 if (!sgl)
 321                                         return -EINVAL;
 322                                 buf_len = sgl->length;
 323                                 p2 = sg_virt(sgl);
 324                         }
 325                         *p2++ = *p++;
 326                         buf_len--;
 327                 }
 328                 y = 0;
 329         }
 330         return 0;
 331 }
 332 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 333
 334 /*
 335  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 336  *                           data from the sgl
 337  *
 338  * This function works in the same way as the mpi_read_raw_data, but it
 339  * takes an sgl instead of void * buffer. i.e. it allocates
 340  * a new MPI and reads the content of the sgl to the MPI.
 341  *
 342  * @sgl:        scatterlist to read from
 343  * @nbytes:     number of bytes to read
 344  *
 345  * Return:      Pointer to a new MPI or NULL on error
 346  */
 347 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 348 {
 349         struct scatterlist *sg;
 350         int x, i, j, z, lzeros, ents;
 351         unsigned int nbits, nlimbs;
 352         mpi_limb_t a;
 353         MPI val = NULL;
 354
 355         lzeros = 0;
 356         ents = sg_nents(sgl);
 357
 358         for_each_sg(sgl, sg, ents, i) {
 359                 const u8 *buff = sg_virt(sg);
 360                 int len = sg->length;
 361
 362                 while (len && !*buff) {
 363                         lzeros++;
 364                         len--;
 365                         buff++;
 366                 }
 367
 368                 if (len && *buff)
 369                         break;
 370
 371                 ents--;
 372                 nbytes -= lzeros;
 373                 lzeros = 0;
 374         }
 375
 376         sgl = sg;
 377         nbytes -= lzeros;
 378         nbits = nbytes * 8;
 379         if (nbits > MAX_EXTERN_MPI_BITS) {
 380                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 381                 return NULL;
 382         }
 383
 384         if (nbytes > 0)
 385                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)) -
 386                         (BITS_PER_LONG - 8);
 387
 388         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 389         val = mpi_alloc(nlimbs);
 390         if (!val)
 391                 return NULL;
 392
 393         val->nbits = nbits;
 394         val->sign = 0;
 395         val->nlimbs = nlimbs;
 396
 397         if (nbytes == 0)
 398                 return val;
 399
 400         j = nlimbs - 1;
 401         a = 0;
 402         z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 403         z %= BYTES_PER_MPI_LIMB;
 404
 405         for_each_sg(sgl, sg, ents, i) {
 406                 const u8 *buffer = sg_virt(sg) + lzeros;
 407                 int len = sg->length - lzeros;
 408
 409                 for (x = 0; x < len; x++) {
 410                         a <<= 8;
 411                         a |= *buffer++;
 412                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 413                                 val->d[j--] = a;
 414                                 a = 0;
 415                         }
 416                 }
 417                 z += x;
 418                 lzeros = 0;
 419         }
 420         return val;
 421 }
 422 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);