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;
  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
  98         nbytes = DIV_ROUND_UP(nbits, 8);
  99         if (nbytes + 2 > *ret_nread) {
 100                 pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
 101                                 nbytes, *ret_nread);
 102                 return ERR_PTR(-EINVAL);
 103         }
 104
 105         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 106         val = mpi_alloc(nlimbs);
 107         if (!val)
 108                 return ERR_PTR(-ENOMEM);
 109         i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 110         i %= BYTES_PER_MPI_LIMB;
 111         val->nbits = nbits;
 112         j = val->nlimbs = nlimbs;
 113         val->sign = 0;
 114         for (; j > 0; j--) {
 115                 a = 0;
 116                 for (; i < BYTES_PER_MPI_LIMB; i++) {
 117                         a <<= 8;
 118                         a |= *buffer++;
 119                 }
 120                 i = 0;
 121                 val->d[j - 1] = a;
 122         }
 123
 124         *ret_nread = nbytes + 2;
 125         return val;
 126 }
 127 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 128
 129 static int count_lzeros(MPI a)
 130 {
 131         mpi_limb_t alimb;
 132         int i, lzeros = 0;
 133
 134         for (i = a->nlimbs - 1; i >= 0; i--) {
 135                 alimb = a->d[i];
 136                 if (alimb == 0) {
 137                         lzeros += sizeof(mpi_limb_t);
 138                 } else {
 139                         lzeros += count_leading_zeros(alimb) / 8;
 140                         break;
 141                 }
 142         }
 143         return lzeros;
 144 }
 145
 146 /**
 147  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 148  *
 149  * @a:          a multi precision integer
 150  * @buf:        bufer to which the output will be written to. Needs to be at
 151  *              leaset mpi_get_size(a) long.
 152  * @buf_len:    size of the buf.
 153  * @nbytes:     receives the actual length of the data written on success and
 154  *              the data to-be-written on -EOVERFLOW in case buf_len was too
 155  *              small.
 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 #if BYTES_PER_MPI_LIMB == 4
 165         __be32 alimb;
 166 #elif BYTES_PER_MPI_LIMB == 8
 167         __be64 alimb;
 168 #else
 169 #error please implement for this limb size.
 170 #endif
 171         unsigned int n = mpi_get_size(a);
 172         int i, lzeros;
 173
 174         if (!buf || !nbytes)
 175                 return -EINVAL;
 176
 177         if (sign)
 178                 *sign = a->sign;
 179
 180         lzeros = count_lzeros(a);
 181
 182         if (buf_len < n - lzeros) {
 183                 *nbytes = n - lzeros;
 184                 return -EOVERFLOW;
 185         }
 186
 187         p = buf;
 188         *nbytes = n - lzeros;
 189
 190         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 191                         lzeros %= BYTES_PER_MPI_LIMB;
 192                 i >= 0; i--) {
 193 #if BYTES_PER_MPI_LIMB == 4
 194                 alimb = cpu_to_be32(a->d[i]);
 195 #elif BYTES_PER_MPI_LIMB == 8
 196                 alimb = cpu_to_be64(a->d[i]);
 197 #else
 198 #error please implement for this limb size.
 199 #endif
 200                 memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
 201                 p += BYTES_PER_MPI_LIMB - lzeros;
 202                 lzeros = 0;
 203         }
 204         return 0;
 205 }
 206 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 207
 208 /*
 209  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 210  * Caller must free the return string.
 211  * This function does return a 0 byte buffer with nbytes set to zero if the
 212  * value of A is zero.
 213  *
 214  * @a:          a multi precision integer.
 215  * @nbytes:     receives the length of this buffer.
 216  * @sign:       if not NULL, it will be set to the sign of the a.
 217  *
 218  * Return:      Pointer to MPI buffer or NULL on error
 219  */
 220 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 221 {
 222         uint8_t *buf;
 223         unsigned int n;
 224         int ret;
 225
 226         if (!nbytes)
 227                 return NULL;
 228
 229         n = mpi_get_size(a);
 230
 231         if (!n)
 232                 n++;
 233
 234         buf = kmalloc(n, GFP_KERNEL);
 235
 236         if (!buf)
 237                 return NULL;
 238
 239         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 240
 241         if (ret) {
 242                 kfree(buf);
 243                 return NULL;
 244         }
 245         return buf;
 246 }
 247 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 248
 249 /**
 250  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 251  *
 252  * This function works in the same way as the mpi_read_buffer, but it
 253  * takes an sgl instead of u8 * buf.
 254  *
 255  * @a:          a multi precision integer
 256  * @sgl:        scatterlist to write to. Needs to be at least
 257  *              mpi_get_size(a) long.
 258  * @nbytes:     in/out param - it has the be set to the maximum number of
 259  *              bytes that can be written to sgl. This has to be at least
 260  *              the size of the integer a. On return it receives the actual
 261  *              length of the data written on success or the data that would
 262  *              be written if buffer was too small.
 263  * @sign:       if not NULL, it will be set to the sign of a.
 264  *
 265  * Return:      0 on success or error code in case of error
 266  */
 267 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
 268                      int *sign)
 269 {
 270         u8 *p, *p2;
 271 #if BYTES_PER_MPI_LIMB == 4
 272         __be32 alimb;
 273 #elif BYTES_PER_MPI_LIMB == 8
 274         __be64 alimb;
 275 #else
 276 #error please implement for this limb size.
 277 #endif
 278         unsigned int n = mpi_get_size(a);
 279         int i, x, y = 0, lzeros, buf_len;
 280
 281         if (!nbytes)
 282                 return -EINVAL;
 283
 284         if (sign)
 285                 *sign = a->sign;
 286
 287         lzeros = count_lzeros(a);
 288
 289         if (*nbytes < n - lzeros) {
 290                 *nbytes = n - lzeros;
 291                 return -EOVERFLOW;
 292         }
 293
 294         *nbytes = n - lzeros;
 295         buf_len = sgl->length;
 296         p2 = sg_virt(sgl);
 297
 298         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 299                         lzeros %= BYTES_PER_MPI_LIMB;
 300                 i >= 0; i--) {
 301 #if BYTES_PER_MPI_LIMB == 4
 302                 alimb = cpu_to_be32(a->d[i]);
 303 #elif BYTES_PER_MPI_LIMB == 8
 304                 alimb = cpu_to_be64(a->d[i]);
 305 #else
 306 #error please implement for this limb size.
 307 #endif
 308                 if (lzeros) {
 309                         y = lzeros;
 310                         lzeros = 0;
 311                 }
 312
 313                 p = (u8 *)&alimb + y;
 314
 315                 for (x = 0; x < sizeof(alimb) - y; x++) {
 316                         if (!buf_len) {
 317                                 sgl = sg_next(sgl);
 318                                 if (!sgl)
 319                                         return -EINVAL;
 320                                 buf_len = sgl->length;
 321                                 p2 = sg_virt(sgl);
 322                         }
 323                         *p2++ = *p++;
 324                         buf_len--;
 325                 }
 326                 y = 0;
 327         }
 328         return 0;
 329 }
 330 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 331
 332 /*
 333  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 334  *                           data from the sgl
 335  *
 336  * This function works in the same way as the mpi_read_raw_data, but it
 337  * takes an sgl instead of void * buffer. i.e. it allocates
 338  * a new MPI and reads the content of the sgl to the MPI.
 339  *
 340  * @sgl:        scatterlist to read from
 341  * @nbytes:     number of bytes to read
 342  *
 343  * Return:      Pointer to a new MPI or NULL on error
 344  */
 345 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 346 {
 347         struct scatterlist *sg;
 348         int x, i, j, z, lzeros, ents;
 349         unsigned int nbits, nlimbs;
 350         mpi_limb_t a;
 351         MPI val = NULL;
 352
 353         lzeros = 0;
 354         ents = sg_nents(sgl);
 355
 356         for_each_sg(sgl, sg, ents, i) {
 357                 const u8 *buff = sg_virt(sg);
 358                 int len = sg->length;
 359
 360                 while (len && !*buff) {
 361                         lzeros++;
 362                         len--;
 363                         buff++;
 364                 }
 365
 366                 if (len && *buff)
 367                         break;
 368
 369                 ents--;
 370                 nbytes -= lzeros;
 371                 lzeros = 0;
 372         }
 373
 374         sgl = sg;
 375         nbytes -= lzeros;
 376         nbits = nbytes * 8;
 377         if (nbits > MAX_EXTERN_MPI_BITS) {
 378                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 379                 return NULL;
 380         }
 381
 382         if (nbytes > 0)
 383                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)) -
 384                         (BITS_PER_LONG - 8);
 385
 386         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 387         val = mpi_alloc(nlimbs);
 388         if (!val)
 389                 return NULL;
 390
 391         val->nbits = nbits;
 392         val->sign = 0;
 393         val->nlimbs = nlimbs;
 394
 395         if (nbytes == 0)
 396                 return val;
 397
 398         j = nlimbs - 1;
 399         a = 0;
 400         z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 401         z %= BYTES_PER_MPI_LIMB;
 402
 403         for_each_sg(sgl, sg, ents, i) {
 404                 const u8 *buffer = sg_virt(sg) + lzeros;
 405                 int len = sg->length - lzeros;
 406
 407                 for (x = 0; x < len; x++) {
 408                         a <<= 8;
 409                         a |= *buffer++;
 410                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 411                                 val->d[j--] = a;
 412                                 a = 0;
 413                         }
 414                 }
 415                 z += x;
 416                 lzeros = 0;
 417         }
 418         return val;
 419 }
 420 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);