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 } 60