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