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 /* We can't use arch_get_random_long() here since alternatives haven't run */ 35 static inline int rdrand_long(unsigned long *v) 36 { 37 int ok; 38 asm volatile("1: " RDRAND_LONG "\n\t" 39 "jc 2f\n\t" 40 "decl %0\n\t" 41 "jnz 1b\n\t" 42 "2:" 43 : "=r" (ok), "=a" (*v) 44 : "0" (RDRAND_RETRY_LOOPS)); 45 return ok; 46 } 47 48 /* 49 * Force a reseed cycle; we are architecturally guaranteed a reseed 50 * after no more than 512 128-bit chunks of random data. This also 51 * acts as a test of the CPU capability. 52 */ 53 #define RESEED_LOOP ((512*128)/sizeof(unsigned long)) 54 55 void __cpuinit x86_init_rdrand(struct cpuinfo_x86 *c) 56 { 57 #ifdef CONFIG_ARCH_RANDOM 58 unsigned long tmp; 59 int i, count, ok; 60 61 if (!cpu_has(c, X86_FEATURE_RDRAND)) 62 return; /* Nothing to do */ 63 64 for (count = i = 0; i < RESEED_LOOP; i++) { 65 ok = rdrand_long(&tmp); 66 if (ok) 67 count++; 68 } 69 70 if (count != RESEED_LOOP) 71 clear_cpu_cap(c, X86_FEATURE_RDRAND); 72 #endif 73 } 74