arch/x86/kernel/cpu/rdrand.c

   1 /*
   2  * This file is part of the Linux kernel.
   3  *
   4  * Copyright (c) 2011, Intel Corporation
   5  * Authors: Fenghua Yu <fenghua.yu@intel.com>,
   6  *          H. Peter Anvin <hpa@linux.intel.com>
   7  *
   8  * This program is free software; you can redistribute it and/or modify it
   9  * under the terms and conditions of the GNU General Public License,
  10  * version 2, as published by the Free Software Foundation.
  11  *
  12  * This program is distributed in the hope it will be useful, but WITHOUT
  13  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  15  * more details.
  16  *
  17  * You should have received a copy of the GNU General Public License along with
  18  * this program; if not, write to the Free Software Foundation, Inc.,
  19  * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  */
  22
  23 #include <asm/processor.h>
  24 #include <asm/archrandom.h>
  25 #include <asm/sections.h>
  26
  27 static int __init x86_rdrand_setup(char *s)
  28 {
  29         setup_clear_cpu_cap(X86_FEATURE_RDRAND);
  30         return 1;
  31 }
  32 __setup("nordrand", x86_rdrand_setup);
  33
  34 /*
  35  * Force a reseed cycle; we are architecturally guaranteed a reseed
  36  * after no more than 512 128-bit chunks of random data.  This also
  37  * acts as a test of the CPU capability.
  38  */
  39 #define RESEED_LOOP ((512*128)/sizeof(unsigned long))
  40
  41 void x86_init_rdrand(struct cpuinfo_x86 *c)
  42 {
  43 #ifdef CONFIG_ARCH_RANDOM
  44         unsigned long tmp;
  45         int i, count, ok;
  46
  47         if (!cpu_has(c, X86_FEATURE_RDRAND))
  48                 return;         /* Nothing to do */
  49
  50         for (count = i = 0; i < RESEED_LOOP; i++) {
  51                 ok = rdrand_long(&tmp);
  52                 if (ok)
  53                         count++;
  54         }
  55
  56         if (count != RESEED_LOOP)
  57                 clear_cpu_cap(c, X86_FEATURE_RDRAND);
  58 #endif
  59 }