diff options
Diffstat (limited to 'arch/x86/kernel/cpu/rdrand.c')
| -rw-r--r-- | arch/x86/kernel/cpu/rdrand.c | 59 |
1 files changed, 25 insertions, 34 deletions
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c index cfa97ff67bda..eeac00d20926 100644 --- a/arch/x86/kernel/cpu/rdrand.c +++ b/arch/x86/kernel/cpu/rdrand.c @@ -1,59 +1,50 @@ +// SPDX-License-Identifier: GPL-2.0-only /* * This file is part of the Linux kernel. * * Copyright (c) 2011, Intel Corporation * Authors: Fenghua Yu <fenghua.yu@intel.com>, * H. Peter Anvin <hpa@linux.intel.com> - * - * This program is free software; you can redistribute it and/or modify it - * under the terms and conditions of the GNU General Public License, - * version 2, as published by the Free Software Foundation. - * - * This program is distributed in the hope it will be useful, but WITHOUT - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for - * more details. - * - * You should have received a copy of the GNU General Public License along with - * this program; if not, write to the Free Software Foundation, Inc., - * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA. - * */ +#include <linux/printk.h> #include <asm/processor.h> #include <asm/archrandom.h> #include <asm/sections.h> -static int __init x86_rdrand_setup(char *s) -{ - setup_clear_cpu_cap(X86_FEATURE_RDRAND); - setup_clear_cpu_cap(X86_FEATURE_RDSEED); - return 1; -} -__setup("nordrand", x86_rdrand_setup); - /* * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation. - * Run the instruction a few times as a sanity check. - * If it fails, it is simple to disable RDRAND here. + * Run the instruction a few times as a sanity check. Also make sure + * it's not outputting the same value over and over, which has happened + * as a result of past CPU bugs. + * + * If it fails, it is simple to disable RDRAND and RDSEED here. */ -#define SANITY_CHECK_LOOPS 8 -#ifdef CONFIG_ARCH_RANDOM void x86_init_rdrand(struct cpuinfo_x86 *c) { - unsigned long tmp; - int i; + enum { SAMPLES = 8, MIN_CHANGE = 5 }; + unsigned long sample, prev; + bool failure = false; + size_t i, changed; if (!cpu_has(c, X86_FEATURE_RDRAND)) return; - for (i = 0; i < SANITY_CHECK_LOOPS; i++) { - if (!rdrand_long(&tmp)) { - clear_cpu_cap(c, X86_FEATURE_RDRAND); - pr_warn_once("rdrand: disabled\n"); - return; + for (changed = 0, i = 0; i < SAMPLES; ++i) { + if (!rdrand_long(&sample)) { + failure = true; + break; } + changed += i && sample != prev; + prev = sample; + } + if (changed < MIN_CHANGE) + failure = true; + + if (failure) { + clear_cpu_cap(c, X86_FEATURE_RDRAND); + clear_cpu_cap(c, X86_FEATURE_RDSEED); + pr_emerg("RDRAND is not reliable on this platform; disabling.\n"); } } -#endif |