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/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2016 Free Software Foundation, Inc.
*
* GRUB 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 3 of the License, or
* (at your option) any later version.
*
* GRUB 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 GRUB. If not, see <http://www.gnu.org/licenses/>.
*/
#include <grub/random.h>
#include <grub/i386/io.h>
#include <grub/i386/tsc.h>
#include <grub/i386/pmtimer.h>
#include <grub/acpi.h>
static int have_tsc = -1, have_pmtimer = -1;
static grub_port_t pmtimer_port;
static int
detect_pmtimer (void)
{
struct grub_acpi_fadt *fadt;
fadt = grub_acpi_find_fadt ();
if (!fadt)
return 0;
pmtimer_port = fadt->pmtimer;
if (!pmtimer_port)
return 0;
return 1;
}
static int
pmtimer_tsc_get_random_bit (void)
{
/* It's hard to come up with figures about pmtimer and tsc jitter but
50 ppm seems to be typical. So we need 10^6/50 tsc cycles to get drift
of one tsc cycle. With TSC at least of 800 MHz it means 1/(50*800)
= 1/40000 s or about 3579545 / 40000 = 90 pmtimer ticks.
This gives us rate of 40000 bit/s or 5 kB/s.
*/
grub_uint64_t tsc_diff;
tsc_diff = grub_pmtimer_wait_count_tsc (pmtimer_port, 90);
if (tsc_diff == 0)
{
have_pmtimer = 0;
return -1;
}
return tsc_diff & 1;
}
static int
pmtimer_tsc_get_random_byte (void)
{
grub_uint8_t ret = 0;
int i, c;
for (i = 0; i < 8; i++)
{
c = pmtimer_tsc_get_random_bit ();
if (c < 0)
return -1;
ret |= c << i;
}
return ret;
}
static int
pmtimer_fill_buffer (void *buffer, grub_size_t sz)
{
grub_uint8_t *p = buffer;
int c;
while (sz)
{
c = pmtimer_tsc_get_random_byte ();
if (c < 0)
return 0;
*p++ = c;
sz--;
}
return 1;
}
int
grub_crypto_arch_get_random (void *buffer, grub_size_t sz)
{
if (have_tsc == -1)
have_tsc = grub_cpu_is_tsc_supported ();
if (!have_tsc)
return 0;
if (have_pmtimer == -1)
have_pmtimer = detect_pmtimer ();
if (!have_pmtimer)
return 0;
return pmtimer_fill_buffer (buffer, sz);
}
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