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:     the number of bytes to write.  Leading bytes will be
 241  *              filled with zero.
 242  * @sign:       if not NULL, it will be set to the sign of a.
 243  *
 244  * Return:      0 on success or error code in case of error
 245  */
 246 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned nbytes,
 247                      int *sign)
 248 {
 249         u8 *p, *p2;
 250 #if BYTES_PER_MPI_LIMB == 4
 251         __be32 alimb;
 252 #elif BYTES_PER_MPI_LIMB == 8
 253         __be64 alimb;
 254 #else
 255 #error please implement for this limb size.
 256 #endif
 257         unsigned int n = mpi_get_size(a);
 258         int i, x, buf_len;
 259
 260         if (sign)
 261                 *sign = a->sign;
 262
 263         if (nbytes < n)
 264                 return -EOVERFLOW;
 265
 266         buf_len = sgl->length;
 267         p2 = sg_virt(sgl);
 268
 269         while (nbytes > n) {
 270                 if (!buf_len) {
 271                         sgl = sg_next(sgl);
 272                         if (!sgl)
 273                                 return -EINVAL;
 274                         buf_len = sgl->length;
 275                         p2 = sg_virt(sgl);
 276                 }
 277
 278                 i = min_t(unsigned, nbytes - n, buf_len);
 279                 memset(p2, 0, i);
 280                 p2 += i;
 281                 buf_len -= i;
 282                 nbytes -= i;
 283         }
 284
 285         for (i = a->nlimbs - 1; i >= 0; i--) {
 286 #if BYTES_PER_MPI_LIMB == 4
 287                 alimb = a->d[i] ? cpu_to_be32(a->d[i]) : 0;
 288 #elif BYTES_PER_MPI_LIMB == 8
 289                 alimb = a->d[i] ? cpu_to_be64(a->d[i]) : 0;
 290 #else
 291 #error please implement for this limb size.
 292 #endif
 293                 p = (u8 *)&alimb;
 294
 295                 for (x = 0; x < sizeof(alimb); x++) {
 296                         if (!buf_len) {
 297                                 sgl = sg_next(sgl);
 298                                 if (!sgl)
 299                                         return -EINVAL;
 300                                 buf_len = sgl->length;
 301                                 p2 = sg_virt(sgl);
 302                         }
 303                         *p2++ = *p++;
 304                         buf_len--;
 305                 }
 306         }
 307         return 0;
 308 }
 309 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 310
 311 /*
 312  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 313  *                           data from the sgl
 314  *
 315  * This function works in the same way as the mpi_read_raw_data, but it
 316  * takes an sgl instead of void * buffer. i.e. it allocates
 317  * a new MPI and reads the content of the sgl to the MPI.
 318  *
 319  * @sgl:        scatterlist to read from
 320  * @nbytes:     number of bytes to read
 321  *
 322  * Return:      Pointer to a new MPI or NULL on error
 323  */
 324 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 325 {
 326         struct scatterlist *sg;
 327         int x, i, j, z, lzeros, ents;
 328         unsigned int nbits, nlimbs;
 329         mpi_limb_t a;
 330         MPI val = NULL;
 331
 332         lzeros = 0;
 333         ents = sg_nents(sgl);
 334
 335         for_each_sg(sgl, sg, ents, i) {
 336                 const u8 *buff = sg_virt(sg);
 337                 int len = sg->length;
 338
 339                 while (len && !*buff) {
 340                         lzeros++;
 341                         len--;
 342                         buff++;
 343                 }
 344
 345                 if (len && *buff)
 346                         break;
 347
 348                 ents--;
 349                 nbytes -= lzeros;
 350                 lzeros = 0;
 351         }
 352
 353         sgl = sg;
 354         nbytes -= lzeros;
 355         nbits = nbytes * 8;
 356         if (nbits > MAX_EXTERN_MPI_BITS) {
 357                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 358                 return NULL;
 359         }
 360
 361         if (nbytes > 0)
 362                 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros)) -
 363                         (BITS_PER_LONG - 8);
 364
 365         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 366         val = mpi_alloc(nlimbs);
 367         if (!val)
 368                 return NULL;
 369
 370         val->nbits = nbits;
 371         val->sign = 0;
 372         val->nlimbs = nlimbs;
 373
 374         if (nbytes == 0)
 375                 return val;
 376
 377         j = nlimbs - 1;
 378         a = 0;
 379         z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 380         z %= BYTES_PER_MPI_LIMB;
 381
 382         for_each_sg(sgl, sg, ents, i) {
 383                 const u8 *buffer = sg_virt(sg) + lzeros;
 384                 int len = sg->length - lzeros;
 385
 386                 for (x = 0; x < len; x++) {
 387                         a <<= 8;
 388                         a |= *buffer++;
 389                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 390                                 val->d[j--] = a;
 391                                 a = 0;
 392                         }
 393                 }
 394                 z += x;
 395                 lzeros = 0;
 396         }
 397         return val;
 398 }
 399 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);