/* mpicoder.c - Coder for the external representation of MPIs
* Copyright (C) 1998, 1999 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* GnuPG is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include <linux/bitops.h>
#include <linux/count_zeros.h>
#include <linux/byteorder/generic.h>
#include <linux/scatterlist.h>
#include <linux/string.h>
#include "mpi-internal.h"
#define MAX_EXTERN_MPI_BITS 16384
/**
* mpi_read_raw_data - Read a raw byte stream as a positive integer
* @xbuffer: The data to read
* @nbytes: The amount of data to read
*/
MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
{
const uint8_t *buffer = xbuffer;
int i, j;
unsigned nbits, nlimbs;
mpi_limb_t a;
MPI val = NULL;
while (nbytes > 0 && buffer[0] == 0) {
buffer++;
nbytes--;
}
nbits = nbytes * 8;
if (nbits > MAX_EXTERN_MPI_BITS) {
pr_info("MPI: mpi too large (%u bits)\n", nbits);
return NULL;
}
if (nbytes > 0)
nbits -= count_leading_zeros(buffer[0]) - (BITS_PER_LONG - 8);
nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
val = mpi_alloc(nlimbs);
if (!val)
return NULL;
val->nbits = nbits;
val->sign = 0;
val->nlimbs = nlimbs;
if (nbytes > 0) {
i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
i %= BYTES_PER_MPI_LIMB;
for (j = nlimbs; j > 0; j--) {
a = 0;
for (; i < BYTES_PER_MPI_LIMB; i++) {
a <<= 8;
a |= *buffer++;
}
i = 0;
val->d[j - 1] = a;
}
}
return val;
}
EXPORT_SYMBOL_GPL(mpi_read_raw_data);
MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
{
const uint8_t *buffer = xbuffer;
unsigned int nbits, nbytes;
MPI val;
if (*ret_nread < 2)
return ERR_PTR(-EINVAL);
nbits = buffer[0] << 8 | buffer[1];
if (nbits > MAX_EXTERN_MPI_BITS) {
pr_info("MPI: mpi too large (%u bits)\n", nbits);
return ERR_PTR(-EINVAL);
}
nbytes = DIV_ROUND_UP(nbits, 8);
if (nbytes + 2 > *ret_nread) {
pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
nbytes, *ret_nread);
return ERR_PTR(-EINVAL);
}
val = mpi_read_raw_data(buffer + 2, nbytes);
if (!val)
return ERR_PTR(-ENOMEM);
*ret_nread = nbytes + 2;
return val;
}
EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
static int count_lzeros(MPI a)
{
mpi_limb_t alimb;
int i, lzeros = 0;
for (i = a->nlimbs - 1; i >= 0; i--) {
alimb = a->d[i];
if (alimb == 0) {
lzeros += sizeof(mpi_limb_t);
} else {
lzeros += count_leading_zeros(alimb) / 8;
break;
}
}
return lzeros;
}
/**
* mpi_read_buffer() - read MPI to a buffer provided by user (msb first)
*
* @a: a multi precision integer
* @buf: buffer to which the output will be written to. Needs to be at
* least mpi_get_size(a) long.
* @buf_len: size of the buf.
* @nbytes: receives the actual length of the data written on success and
* the data to-be-written on -EOVERFLOW in case buf_len was too
* small.
* @sign: if not NULL, it will be set to the sign of a.
*
* Return: 0 on success or error code in case of error
*/
int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
int *sign)
{
uint8_t *p;
#if BYTES_PER_MPI_LIMB == 4
__be32 alimb;
#elif BYTES_PER_MPI_LIMB == 8
__be64 alimb;
#else
#error please implement for this limb size.
#endif
unsigned int n = mpi_get_size(a);
int i, lzeros;
if (!buf || !nbytes)
return -EINVAL;
if (sign)
*sign = a->sign;
lzeros = count_lzeros(a);
if (buf_len < n - lzeros) {
*nbytes = n - lzeros;
return -EOVERFLOW;
}
p = buf;
*nbytes = n - lzeros;
for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
lzeros %= BYTES_PER_MPI_LIMB;
i >= 0; i--) {
#if BYTES_PER_MPI_LIMB == 4
alimb = cpu_to_be32(a->d[i]);
#elif BYTES_PER_MPI_LIMB == 8
alimb = cpu_to_be64(a->d[i]);
#else
#error please implement for this limb size.
#endif
memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
p += BYTES_PER_MPI_LIMB - lzeros;
lzeros = 0;
}
return 0;
}
EXPORT_SYMBOL_GPL(mpi_read_buffer);
/*
* mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
* Caller must free the return string.
* This function does return a 0 byte buffer with nbytes set to zero if the
* value of A is zero.
*
* @a: a multi precision integer.
* @nbytes: receives the length of this buffer.
* @sign: if not NULL, it will be set to the sign of the a.
*
* Return: Pointer to MPI buffer or NULL on error
*/
void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
{
uint8_t *buf;
unsigned int n;
int ret;
if (!nbytes)
return NULL;
n = mpi_get_size(a);
if (!n)
n++;
buf = kmalloc(n, GFP_KERNEL);
if (!buf)
return NULL;
ret = mpi_read_buffer(a, buf, n, nbytes, sign);
if (ret) {
kfree(buf);
return NULL;
}
return buf;
}
EXPORT_SYMBOL_GPL(mpi_get_buffer);
/**
* mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
*
* This function works in the same way as the mpi_read_buffer, but it
* takes an sgl instead of u8 * buf.
*
* @a: a multi precision integer
* @sgl: scatterlist to write to. Needs to be at least
* mpi_get_size(a) long.
* @nbytes: the number of bytes to write. Leading bytes will be
* filled with zero.
* @sign: if not NULL, it will be set to the sign of a.
*
* Return: 0 on success or error code in case of error
*/
int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned nbytes,
int *sign)
{
u8 *p, *p2;
#if BYTES_PER_MPI_LIMB == 4
__be32 alimb;
#elif BYTES_PER_MPI_LIMB == 8
__be64 alimb;
#else
#error please implement for this limb size.
#endif
unsigned int n = mpi_get_size(a);
struct sg_mapping_iter miter;
int i, x, buf_len;
int nents;
if (sign)
*sign = a->sign;
if (nbytes < n)
return -EOVERFLOW;
nents = sg_nents_for_len(sgl, nbytes);
if (nents < 0)
return -EINVAL;
sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
sg_miter_next(&miter);
buf_len = miter.length;
p2 = miter.addr;
while (nbytes > n) {
i = min_t(unsigned, nbytes - n, buf_len);
memset(p2, 0, i);
p2 += i;
nbytes -= i;
buf_len -= i;
if (!buf_len) {
sg_miter_next(&miter);
buf_len = miter.length;
p2 = miter.addr;
}
}
for (i = a->nlimbs - 1; i >= 0; i--) {
#if BYTES_PER_MPI_LIMB == 4
alimb = a->d[i] ? cpu_to_be32(a->d[i]) : 0;
#elif BYTES_PER_MPI_LIMB == 8
alimb = a->d[i] ? cpu_to_be64(a->d[i]) : 0;
#else
#error please implement for this limb size.
#endif
p = (u8 *)&alimb;
for (x = 0; x < sizeof(alimb); x++) {
*p2++ = *p++;
if (!--buf_len) {
sg_miter_next(&miter);
buf_len = miter.length;
p2 = miter.addr;
}
}
}
sg_miter_stop(&miter);
return 0;
}
EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
/*
* mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
* data from the sgl
*
* This function works in the same way as the mpi_read_raw_data, but it
* takes an sgl instead of void * buffer. i.e. it allocates
* a new MPI and reads the content of the sgl to the MPI.
*
* @sgl: scatterlist to read from
* @nbytes: number of bytes to read
*
* Return: Pointer to a new MPI or NULL on error
*/
MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
{
struct sg_mapping_iter miter;
unsigned int nbits, nlimbs;
int x, j, z, lzeros, ents;
unsigned int len;
const u8 *buff;
mpi_limb_t a;
MPI val = NULL;
ents = sg_nents_for_len(sgl, nbytes);
if (ents < 0)
return NULL;
sg_miter_start(&miter, sgl, ents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);
lzeros = 0;
len = 0;
while (nbytes > 0) {
while (len && !*buff) {
lzeros++;
len--;
buff++;
}
if (len && *buff)
break;
sg_miter_next(&miter);
buff = miter.addr;
len = miter.length;
nbytes -= lzeros;
lzeros = 0;
}
miter.consumed = lzeros;
nbytes -= lzeros;
nbits = nbytes * 8;
if (nbits > MAX_EXTERN_MPI_BITS) {
sg_miter_stop(&miter);
pr_info("MPI: mpi too large (%u bits)\n", nbits);
return NULL;
}
if (nbytes > 0)
nbits -= count_leading_zeros(*buff) - (BITS_PER_LONG - 8);
sg_miter_stop(&miter);
nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
val = mpi_alloc(nlimbs);
if (!val)
return NULL;
val->nbits = nbits;
val->sign = 0;
val->nlimbs = nlimbs;
if (nbytes == 0)
return val;
j = nlimbs - 1;
a = 0;
z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
z %= BYTES_PER_MPI_LIMB;
while (sg_miter_next(&miter)) {
buff = miter.addr;
len = min_t(unsigned, miter.length, nbytes);
nbytes -= len;
for (x = 0; x < len; x++) {
a <<= 8;
a |= *buff++;
if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
val->d[j--] = a;
a = 0;
}
}
z += x;
}
return val;
}
EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);
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