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 "mpi-internal.h"
24
25 #define MAX_EXTERN_MPI_BITS 16384
26
27 /**
28 * mpi_read_raw_data - Read a raw byte stream as a positive integer
29 * @xbuffer: The data to read
30 * @nbytes: The amount of data to read
31 */
mpi_read_raw_data(const void * xbuffer,size_t nbytes)32 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
33 {
34 const uint8_t *buffer = xbuffer;
35 int i, j;
36 unsigned nbits, nlimbs;
37 mpi_limb_t a;
38 MPI val = NULL;
39
40 while (nbytes > 0 && buffer[0] == 0) {
41 buffer++;
42 nbytes--;
43 }
44
45 nbits = nbytes * 8;
46 if (nbits > MAX_EXTERN_MPI_BITS) {
47 pr_info("MPI: mpi too large (%u bits)\n", nbits);
48 return NULL;
49 }
50 if (nbytes > 0)
51 nbits -= count_leading_zeros(buffer[0]);
52 else
53 nbits = 0;
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
mpi_read_from_buffer(const void * xbuffer,unsigned * ret_nread)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 goto leave;
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 goto leave;
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 NULL;
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
count_lzeros(MPI a)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.
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 */
mpi_read_buffer(MPI a,uint8_t * buf,unsigned buf_len,unsigned * nbytes,int * sign)160 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
161 int *sign)
162 {
163 uint8_t *p;
164 mpi_limb_t alimb;
165 unsigned int n = mpi_get_size(a);
166 int i, lzeros;
167
168 if (buf_len < n || !buf || !nbytes)
169 return -EINVAL;
170
171 if (sign)
172 *sign = a->sign;
173
174 lzeros = count_lzeros(a);
175
176 p = buf;
177 *nbytes = n - lzeros;
178
179 for (i = a->nlimbs - 1; i >= 0; i--) {
180 alimb = a->d[i];
181 #if BYTES_PER_MPI_LIMB == 4
182 *p++ = alimb >> 24;
183 *p++ = alimb >> 16;
184 *p++ = alimb >> 8;
185 *p++ = alimb;
186 #elif BYTES_PER_MPI_LIMB == 8
187 *p++ = alimb >> 56;
188 *p++ = alimb >> 48;
189 *p++ = alimb >> 40;
190 *p++ = alimb >> 32;
191 *p++ = alimb >> 24;
192 *p++ = alimb >> 16;
193 *p++ = alimb >> 8;
194 *p++ = alimb;
195 #else
196 #error please implement for this limb size.
197 #endif
198
199 if (lzeros > 0) {
200 if (lzeros >= sizeof(alimb)) {
201 p -= sizeof(alimb);
202 } else {
203 mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
204 mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
205 + lzeros;
206 *limb1 = *limb2;
207 p -= lzeros;
208 }
209 lzeros -= sizeof(alimb);
210 }
211 }
212 return 0;
213 }
214 EXPORT_SYMBOL_GPL(mpi_read_buffer);
215
216 /*
217 * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
218 * Caller must free the return string.
219 * This function does return a 0 byte buffer with nbytes set to zero if the
220 * value of A is zero.
221 *
222 * @a: a multi precision integer.
223 * @nbytes: receives the length of this buffer.
224 * @sign: if not NULL, it will be set to the sign of the a.
225 *
226 * Return: Pointer to MPI buffer or NULL on error
227 */
mpi_get_buffer(MPI a,unsigned * nbytes,int * sign)228 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
229 {
230 uint8_t *buf;
231 unsigned int n;
232 int ret;
233
234 if (!nbytes)
235 return NULL;
236
237 n = mpi_get_size(a);
238
239 if (!n)
240 n++;
241
242 buf = kmalloc(n, GFP_KERNEL);
243
244 if (!buf)
245 return NULL;
246
247 ret = mpi_read_buffer(a, buf, n, nbytes, sign);
248
249 if (ret) {
250 kfree(buf);
251 return NULL;
252 }
253 return buf;
254 }
255 EXPORT_SYMBOL_GPL(mpi_get_buffer);
256
257 /****************
258 * Use BUFFER to update MPI.
259 */
mpi_set_buffer(MPI a,const void * xbuffer,unsigned nbytes,int sign)260 int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
261 {
262 const uint8_t *buffer = xbuffer, *p;
263 mpi_limb_t alimb;
264 int nlimbs;
265 int i;
266
267 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
268 if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
269 return -ENOMEM;
270 a->sign = sign;
271
272 for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
273 #if BYTES_PER_MPI_LIMB == 4
274 alimb = (mpi_limb_t) *p--;
275 alimb |= (mpi_limb_t) *p-- << 8;
276 alimb |= (mpi_limb_t) *p-- << 16;
277 alimb |= (mpi_limb_t) *p-- << 24;
278 #elif BYTES_PER_MPI_LIMB == 8
279 alimb = (mpi_limb_t) *p--;
280 alimb |= (mpi_limb_t) *p-- << 8;
281 alimb |= (mpi_limb_t) *p-- << 16;
282 alimb |= (mpi_limb_t) *p-- << 24;
283 alimb |= (mpi_limb_t) *p-- << 32;
284 alimb |= (mpi_limb_t) *p-- << 40;
285 alimb |= (mpi_limb_t) *p-- << 48;
286 alimb |= (mpi_limb_t) *p-- << 56;
287 #else
288 #error please implement for this limb size.
289 #endif
290 a->d[i++] = alimb;
291 }
292 if (p >= buffer) {
293 #if BYTES_PER_MPI_LIMB == 4
294 alimb = *p--;
295 if (p >= buffer)
296 alimb |= (mpi_limb_t) *p-- << 8;
297 if (p >= buffer)
298 alimb |= (mpi_limb_t) *p-- << 16;
299 if (p >= buffer)
300 alimb |= (mpi_limb_t) *p-- << 24;
301 #elif BYTES_PER_MPI_LIMB == 8
302 alimb = (mpi_limb_t) *p--;
303 if (p >= buffer)
304 alimb |= (mpi_limb_t) *p-- << 8;
305 if (p >= buffer)
306 alimb |= (mpi_limb_t) *p-- << 16;
307 if (p >= buffer)
308 alimb |= (mpi_limb_t) *p-- << 24;
309 if (p >= buffer)
310 alimb |= (mpi_limb_t) *p-- << 32;
311 if (p >= buffer)
312 alimb |= (mpi_limb_t) *p-- << 40;
313 if (p >= buffer)
314 alimb |= (mpi_limb_t) *p-- << 48;
315 if (p >= buffer)
316 alimb |= (mpi_limb_t) *p-- << 56;
317 #else
318 #error please implement for this limb size.
319 #endif
320 a->d[i++] = alimb;
321 }
322 a->nlimbs = i;
323
324 if (i != nlimbs) {
325 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
326 nlimbs);
327 BUG();
328 }
329 return 0;
330 }
331 EXPORT_SYMBOL_GPL(mpi_set_buffer);
332
333 /**
334 * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
335 *
336 * This function works in the same way as the mpi_read_buffer, but it
337 * takes an sgl instead of u8 * buf.
338 *
339 * @a: a multi precision integer
340 * @sgl: scatterlist to write to. Needs to be at least
341 * mpi_get_size(a) long.
342 * @nbytes: in/out param - it has the be set to the maximum number of
343 * bytes that can be written to sgl. This has to be at least
344 * the size of the integer a. On return it receives the actual
345 * length of the data written.
346 * @sign: if not NULL, it will be set to the sign of a.
347 *
348 * Return: 0 on success or error code in case of error
349 */
mpi_write_to_sgl(MPI a,struct scatterlist * sgl,unsigned * nbytes,int * sign)350 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned *nbytes,
351 int *sign)
352 {
353 u8 *p, *p2;
354 mpi_limb_t alimb, alimb2;
355 unsigned int n = mpi_get_size(a);
356 int i, x, y = 0, lzeros, buf_len;
357
358 if (!nbytes || *nbytes < n)
359 return -EINVAL;
360
361 if (sign)
362 *sign = a->sign;
363
364 lzeros = count_lzeros(a);
365
366 *nbytes = n - lzeros;
367 buf_len = sgl->length;
368 p2 = sg_virt(sgl);
369
370 for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
371 lzeros %= BYTES_PER_MPI_LIMB;
372 i >= 0; i--) {
373 alimb = a->d[i];
374 p = (u8 *)&alimb2;
375 #if BYTES_PER_MPI_LIMB == 4
376 *p++ = alimb >> 24;
377 *p++ = alimb >> 16;
378 *p++ = alimb >> 8;
379 *p++ = alimb;
380 #elif BYTES_PER_MPI_LIMB == 8
381 *p++ = alimb >> 56;
382 *p++ = alimb >> 48;
383 *p++ = alimb >> 40;
384 *p++ = alimb >> 32;
385 *p++ = alimb >> 24;
386 *p++ = alimb >> 16;
387 *p++ = alimb >> 8;
388 *p++ = alimb;
389 #else
390 #error please implement for this limb size.
391 #endif
392 if (lzeros > 0) {
393 mpi_limb_t *limb1 = (void *)p - sizeof(alimb);
394 mpi_limb_t *limb2 = (void *)p - sizeof(alimb)
395 + lzeros;
396 *limb1 = *limb2;
397 p -= lzeros;
398 y = lzeros;
399 lzeros -= sizeof(alimb);
400 }
401
402 p = p - (sizeof(alimb) - y);
403
404 for (x = 0; x < sizeof(alimb) - y; x++) {
405 if (!buf_len) {
406 sgl = sg_next(sgl);
407 if (!sgl)
408 return -EINVAL;
409 buf_len = sgl->length;
410 p2 = sg_virt(sgl);
411 }
412 *p2++ = *p++;
413 buf_len--;
414 }
415 y = 0;
416 }
417 return 0;
418 }
419 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
420
421 /*
422 * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
423 * data from the sgl
424 *
425 * This function works in the same way as the mpi_read_raw_data, but it
426 * takes an sgl instead of void * buffer. i.e. it allocates
427 * a new MPI and reads the content of the sgl to the MPI.
428 *
429 * @sgl: scatterlist to read from
430 * @len: number of bytes to read
431 *
432 * Return: Pointer to a new MPI or NULL on error
433 */
mpi_read_raw_from_sgl(struct scatterlist * sgl,unsigned int len)434 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int len)
435 {
436 struct scatterlist *sg;
437 int x, i, j, z, lzeros, ents;
438 unsigned int nbits, nlimbs, nbytes;
439 mpi_limb_t a;
440 MPI val = NULL;
441
442 lzeros = 0;
443 ents = sg_nents(sgl);
444
445 for_each_sg(sgl, sg, ents, i) {
446 const u8 *buff = sg_virt(sg);
447 int len = sg->length;
448
449 while (len && !*buff) {
450 lzeros++;
451 len--;
452 buff++;
453 }
454
455 if (len && *buff)
456 break;
457
458 ents--;
459 lzeros = 0;
460 }
461
462 sgl = sg;
463
464 if (!ents)
465 nbytes = 0;
466 else
467 nbytes = len - lzeros;
468
469 nbits = nbytes * 8;
470 if (nbits > MAX_EXTERN_MPI_BITS) {
471 pr_info("MPI: mpi too large (%u bits)\n", nbits);
472 return NULL;
473 }
474
475 if (nbytes > 0)
476 nbits -= count_leading_zeros(*(u8 *)(sg_virt(sgl) + lzeros));
477 else
478 nbits = 0;
479
480 nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
481 val = mpi_alloc(nlimbs);
482 if (!val)
483 return NULL;
484
485 val->nbits = nbits;
486 val->sign = 0;
487 val->nlimbs = nlimbs;
488
489 if (nbytes == 0)
490 return val;
491
492 j = nlimbs - 1;
493 a = 0;
494 z = 0;
495 x = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
496 x %= BYTES_PER_MPI_LIMB;
497
498 for_each_sg(sgl, sg, ents, i) {
499 const u8 *buffer = sg_virt(sg) + lzeros;
500 int len = sg->length - lzeros;
501 int buf_shift = x;
502
503 if (sg_is_last(sg) && (len % BYTES_PER_MPI_LIMB))
504 len += BYTES_PER_MPI_LIMB - (len % BYTES_PER_MPI_LIMB);
505
506 for (; x < len + buf_shift; x++) {
507 a <<= 8;
508 a |= *buffer++;
509 if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
510 val->d[j--] = a;
511 a = 0;
512 }
513 }
514 z += x;
515 x = 0;
516 lzeros = 0;
517 }
518 return val;
519 }
520 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);
521