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104 lines
2.4 KiB
C
104 lines
2.4 KiB
C
/*
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* GRUB -- GRand Unified Bootloader
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* Copyright (C) 2016 Free Software Foundation, Inc.
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*
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* GRUB is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* GRUB is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GRUB. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include <grub/random.h>
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#include <grub/i386/io.h>
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#include <grub/i386/tsc.h>
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#include <grub/i386/pmtimer.h>
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#include <grub/acpi.h>
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static int have_tsc = -1, have_pmtimer = -1;
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static grub_port_t pmtimer_port;
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static int
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detect_pmtimer (void)
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{
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struct grub_acpi_fadt *fadt;
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fadt = grub_acpi_find_fadt ();
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if (!fadt)
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return 0;
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pmtimer_port = fadt->pmtimer;
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if (!pmtimer_port)
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return 0;
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return 1;
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}
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static int
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pmtimer_tsc_get_random_bit (void)
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{
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/* It's hard to come up with figures about pmtimer and tsc jitter but
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50 ppm seems to be typical. So we need 10^6/50 tsc cycles to get drift
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of one tsc cycle. With TSC at least of 800 MHz it means 1/(50*800)
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= 1/40000 s or about 3579545 / 40000 = 90 pmtimer ticks.
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This gives us rate of 40000 bit/s or 5 kB/s.
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*/
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grub_uint64_t tsc_diff;
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tsc_diff = grub_pmtimer_wait_count_tsc (pmtimer_port, 90);
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if (tsc_diff == 0)
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{
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have_pmtimer = 0;
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return -1;
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}
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return tsc_diff & 1;
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}
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static int
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pmtimer_tsc_get_random_byte (void)
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{
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grub_uint8_t ret = 0;
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int i, c;
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for (i = 0; i < 8; i++)
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{
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c = pmtimer_tsc_get_random_bit ();
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if (c < 0)
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return -1;
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ret |= c << i;
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}
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return ret;
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}
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static int
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pmtimer_fill_buffer (void *buffer, grub_size_t sz)
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{
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grub_uint8_t *p = buffer;
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int c;
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while (sz)
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{
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c = pmtimer_tsc_get_random_byte ();
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if (c < 0)
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return 0;
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*p++ = c;
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sz--;
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}
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return 1;
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}
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int
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grub_crypto_arch_get_random (void *buffer, grub_size_t sz)
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{
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if (have_tsc == -1)
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have_tsc = grub_cpu_is_tsc_supported ();
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if (!have_tsc)
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return 0;
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if (have_pmtimer == -1)
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have_pmtimer = detect_pmtimer ();
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if (!have_pmtimer)
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return 0;
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return pmtimer_fill_buffer (buffer, sz);
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}
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