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/scatterlist.h>
25 #include <linux/string.h>
26 #include "mpi-internal.h"
27
28 #define MAX_EXTERN_MPI_BITS 16384
29
30 /**
31 * mpi_read_raw_data - Read a raw byte stream as a positive integer
32 * @xbuffer: The data to read
33 * @nbytes: The amount of data to read
34 */
mpi_read_raw_data(const void * xbuffer,size_t nbytes)35 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
36 {
37 const uint8_t *buffer = xbuffer;
38 int i, j;
39 unsigned nbits, nlimbs;
40 mpi_limb_t a;
41 MPI val = NULL;
42
43 while (nbytes > 0 && buffer[0] == 0) {
44 buffer++;
45 nbytes--;
46 }
47
48 nbits = nbytes * 8;
49 if (nbits > MAX_EXTERN_MPI_BITS) {
50 pr_info("MPI: mpi too large (%u bits)\n", nbits);
51 return NULL;
52 }
53 if (nbytes > 0)
54 nbits -= count_leading_zeros(buffer[0]) - (BITS_PER_LONG - 8);
55
56 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
57 val = mpi_alloc(nlimbs);
58 if (!val)
59 return NULL;
60 val->nbits = nbits;
61 val->sign = 0;
62 val->nlimbs = nlimbs;
63
64 if (nbytes > 0) {
65 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
66 i %= BYTES_PER_MPI_LIMB;
67 for (j = nlimbs; j > 0; j--) {
68 a = 0;
69 for (; i < BYTES_PER_MPI_LIMB; i++) {
70 a <<= 8;
71 a |= *buffer++;
72 }
73 i = 0;
74 val->d[j - 1] = a;
75 }
76 }
77 return val;
78 }
79 EXPORT_SYMBOL_GPL(mpi_read_raw_data);
80
mpi_read_from_buffer(const void * xbuffer,unsigned * ret_nread)81 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
82 {
83 const uint8_t *buffer = xbuffer;
84 unsigned int nbits, nbytes;
85 MPI val;
86
87 if (*ret_nread < 2)
88 return ERR_PTR(-EINVAL);
89 nbits = buffer[0] << 8 | buffer[1];
90
91 if (nbits > MAX_EXTERN_MPI_BITS) {
92 pr_info("MPI: mpi too large (%u bits)\n", nbits);
93 return ERR_PTR(-EINVAL);
94 }
95
96 nbytes = DIV_ROUND_UP(nbits, 8);
97 if (nbytes + 2 > *ret_nread) {
98 pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
99 nbytes, *ret_nread);
100 return ERR_PTR(-EINVAL);
101 }
102
103 val = mpi_read_raw_data(buffer + 2, nbytes);
104 if (!val)
105 return ERR_PTR(-ENOMEM);
106
107 *ret_nread = nbytes + 2;
108 return val;
109 }
110 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
111
count_lzeros(MPI a)112 static int count_lzeros(MPI a)
113 {
114 mpi_limb_t alimb;
115 int i, lzeros = 0;
116
117 for (i = a->nlimbs - 1; i >= 0; i--) {
118 alimb = a->d[i];
119 if (alimb == 0) {
120 lzeros += sizeof(mpi_limb_t);
121 } else {
122 lzeros += count_leading_zeros(alimb) / 8;
123 break;
124 }
125 }
126 return lzeros;
127 }
128
129 /**
130 * mpi_read_buffer() - read MPI to a buffer provided by user (msb first)
131 *
132 * @a: a multi precision integer
133 * @buf: buffer to which the output will be written to. Needs to be at
134 * least mpi_get_size(a) long.
135 * @buf_len: size of the buf.
136 * @nbytes: receives the actual length of the data written on success and
137 * the data to-be-written on -EOVERFLOW in case buf_len was too
138 * small.
139 * @sign: if not NULL, it will be set to the sign of a.
140 *
141 * Return: 0 on success or error code in case of error
142 */
mpi_read_buffer(MPI a,uint8_t * buf,unsigned buf_len,unsigned * nbytes,int * sign)143 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
144 int *sign)
145 {
146 uint8_t *p;
147 #if BYTES_PER_MPI_LIMB == 4
148 __be32 alimb;
149 #elif BYTES_PER_MPI_LIMB == 8
150 __be64 alimb;
151 #else
152 #error please implement for this limb size.
153 #endif
154 unsigned int n = mpi_get_size(a);
155 int i, lzeros;
156
157 if (!buf || !nbytes)
158 return -EINVAL;
159
160 if (sign)
161 *sign = a->sign;
162
163 lzeros = count_lzeros(a);
164
165 if (buf_len < n - lzeros) {
166 *nbytes = n - lzeros;
167 return -EOVERFLOW;
168 }
169
170 p = buf;
171 *nbytes = n - lzeros;
172
173 for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
174 lzeros %= BYTES_PER_MPI_LIMB;
175 i >= 0; i--) {
176 #if BYTES_PER_MPI_LIMB == 4
177 alimb = cpu_to_be32(a->d[i]);
178 #elif BYTES_PER_MPI_LIMB == 8
179 alimb = cpu_to_be64(a->d[i]);
180 #else
181 #error please implement for this limb size.
182 #endif
183 memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
184 p += BYTES_PER_MPI_LIMB - lzeros;
185 lzeros = 0;
186 }
187 return 0;
188 }
189 EXPORT_SYMBOL_GPL(mpi_read_buffer);
190
191 /*
192 * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
193 * Caller must free the return string.
194 * This function does return a 0 byte buffer with nbytes set to zero if the
195 * value of A is zero.
196 *
197 * @a: a multi precision integer.
198 * @nbytes: receives the length of this buffer.
199 * @sign: if not NULL, it will be set to the sign of the a.
200 *
201 * Return: Pointer to MPI buffer or NULL on error
202 */
mpi_get_buffer(MPI a,unsigned * nbytes,int * sign)203 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
204 {
205 uint8_t *buf;
206 unsigned int n;
207 int ret;
208
209 if (!nbytes)
210 return NULL;
211
212 n = mpi_get_size(a);
213
214 if (!n)
215 n++;
216
217 buf = kmalloc(n, GFP_KERNEL);
218
219 if (!buf)
220 return NULL;
221
222 ret = mpi_read_buffer(a, buf, n, nbytes, sign);
223
224 if (ret) {
225 kfree(buf);
226 return NULL;
227 }
228 return buf;
229 }
230 EXPORT_SYMBOL_GPL(mpi_get_buffer);
231
232 /**
233 * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
234 *
235 * This function works in the same way as the mpi_read_buffer, but it
236 * takes an sgl instead of u8 * buf.
237 *
238 * @a: a multi precision integer
239 * @sgl: scatterlist to write to. Needs to be at least
240 * mpi_get_size(a) long.
241 * @nbytes: the number of bytes to write. Leading bytes will be
242 * filled with zero.
243 * @sign: if not NULL, it will be set to the sign of a.
244 *
245 * Return: 0 on success or error code in case of error
246 */
mpi_write_to_sgl(MPI a,struct scatterlist * sgl,unsigned nbytes,int * sign)247 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned nbytes,
248 int *sign)
249 {
250 u8 *p, *p2;
251 #if BYTES_PER_MPI_LIMB == 4
252 __be32 alimb;
253 #elif BYTES_PER_MPI_LIMB == 8
254 __be64 alimb;
255 #else
256 #error please implement for this limb size.
257 #endif
258 unsigned int n = mpi_get_size(a);
259 struct sg_mapping_iter miter;
260 int i, x, buf_len;
261 int nents;
262
263 if (sign)
264 *sign = a->sign;
265
266 if (nbytes < n)
267 return -EOVERFLOW;
268
269 nents = sg_nents_for_len(sgl, nbytes);
270 if (nents < 0)
271 return -EINVAL;
272
273 sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
274 sg_miter_next(&miter);
275 buf_len = miter.length;
276 p2 = miter.addr;
277
278 while (nbytes > n) {
279 i = min_t(unsigned, nbytes - n, buf_len);
280 memset(p2, 0, i);
281 p2 += i;
282 nbytes -= i;
283
284 buf_len -= i;
285 if (!buf_len) {
286 sg_miter_next(&miter);
287 buf_len = miter.length;
288 p2 = miter.addr;
289 }
290 }
291
292 for (i = a->nlimbs - 1; i >= 0; i--) {
293 #if BYTES_PER_MPI_LIMB == 4
294 alimb = a->d[i] ? cpu_to_be32(a->d[i]) : 0;
295 #elif BYTES_PER_MPI_LIMB == 8
296 alimb = a->d[i] ? cpu_to_be64(a->d[i]) : 0;
297 #else
298 #error please implement for this limb size.
299 #endif
300 p = (u8 *)&alimb;
301
302 for (x = 0; x < sizeof(alimb); x++) {
303 *p2++ = *p++;
304 if (!--buf_len) {
305 sg_miter_next(&miter);
306 buf_len = miter.length;
307 p2 = miter.addr;
308 }
309 }
310 }
311
312 sg_miter_stop(&miter);
313 return 0;
314 }
315 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
316
317 /*
318 * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
319 * data from the sgl
320 *
321 * This function works in the same way as the mpi_read_raw_data, but it
322 * takes an sgl instead of void * buffer. i.e. it allocates
323 * a new MPI and reads the content of the sgl to the MPI.
324 *
325 * @sgl: scatterlist to read from
326 * @nbytes: number of bytes to read
327 *
328 * Return: Pointer to a new MPI or NULL on error
329 */
mpi_read_raw_from_sgl(struct scatterlist * sgl,unsigned int nbytes)330 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
331 {
332 struct sg_mapping_iter miter;
333 unsigned int nbits, nlimbs;
334 int x, j, z, lzeros, ents;
335 unsigned int len;
336 const u8 *buff;
337 mpi_limb_t a;
338 MPI val = NULL;
339
340 ents = sg_nents_for_len(sgl, nbytes);
341 if (ents < 0)
342 return NULL;
343
344 sg_miter_start(&miter, sgl, ents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);
345
346 lzeros = 0;
347 len = 0;
348 while (nbytes > 0) {
349 while (len && !*buff) {
350 lzeros++;
351 len--;
352 buff++;
353 }
354
355 if (len && *buff)
356 break;
357
358 sg_miter_next(&miter);
359 buff = miter.addr;
360 len = miter.length;
361
362 nbytes -= lzeros;
363 lzeros = 0;
364 }
365
366 miter.consumed = lzeros;
367
368 nbytes -= lzeros;
369 nbits = nbytes * 8;
370 if (nbits > MAX_EXTERN_MPI_BITS) {
371 sg_miter_stop(&miter);
372 pr_info("MPI: mpi too large (%u bits)\n", nbits);
373 return NULL;
374 }
375
376 if (nbytes > 0)
377 nbits -= count_leading_zeros(*buff) - (BITS_PER_LONG - 8);
378
379 sg_miter_stop(&miter);
380
381 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
382 val = mpi_alloc(nlimbs);
383 if (!val)
384 return NULL;
385
386 val->nbits = nbits;
387 val->sign = 0;
388 val->nlimbs = nlimbs;
389
390 if (nbytes == 0)
391 return val;
392
393 j = nlimbs - 1;
394 a = 0;
395 z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
396 z %= BYTES_PER_MPI_LIMB;
397
398 while (sg_miter_next(&miter)) {
399 buff = miter.addr;
400 len = min_t(unsigned, miter.length, nbytes);
401 nbytes -= len;
402
403 for (x = 0; x < len; x++) {
404 a <<= 8;
405 a |= *buff++;
406 if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
407 val->d[j--] = a;
408 a = 0;
409 }
410 }
411 z += x;
412 }
413
414 return val;
415 }
416 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);
417