1 files changed, 103 insertions, 0 deletions
diff --git a/grub-core/lib/i386/random.c b/grub-core/lib/i386/random.c
new file mode 100644
index 0000000..cd83d2f
--- /dev/null
+++ b/grub-core/lib/i386/random.c
@@ -0,0 +1,103 @@
+/*
+ *  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);
+}