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 void x86_init_rdrand(struct cpuinfo_x86 *c) 43 { 44 #ifdef CONFIG_ARCH_RANDOM 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 #endif 59 } 60