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         setup_clear_cpu_cap(X86_FEATURE_RDSEED);
  31         return 1;
  32 }
  33 __setup("nordrand", x86_rdrand_setup);
  34
  35 /*
  36  * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
  37  * Run the instruction a few times as a sanity check.
  38  * If it fails, it is simple to disable RDRAND here.
  39  */
  40 #define SANITY_CHECK_LOOPS 8
  41
  42 #ifdef CONFIG_ARCH_RANDOM
  43 void x86_init_rdrand(struct cpuinfo_x86 *c)
  44 {
  45         unsigned long tmp;
  46         int i;
  47
  48         if (!cpu_has(c, X86_FEATURE_RDRAND))
  49                 return;
  50
  51         for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
  52                 if (!rdrand_long(&tmp)) {
  53                         clear_cpu_cap(c, X86_FEATURE_RDRAND);
  54                         pr_warn_once("rdrand: disabled\n");
  55                         return;
  56                 }
  57         }
  58 }
  59 #endif