1// SPDX-License-Identifier: GPL-2.0-only
 2/*
 3 * This file is part of the Linux kernel.
 4 *
 5 * Copyright (c) 2011, Intel Corporation
 6 * Authors: Fenghua Yu <fenghua.yu@intel.com>,
 7 *          H. Peter Anvin <hpa@linux.intel.com>
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 8 */
 9#include <linux/printk.h>
10
11#include <asm/processor.h>
12#include <asm/archrandom.h>
13#include <asm/sections.h>
14
 
 
 
 
 
 
 
 
15/*
16 * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
17 * Run the instruction a few times as a sanity check. Also make sure
18 * it's not outputting the same value over and over, which has happened
19 * as a result of past CPU bugs.
20 *
21 * If it fails, it is simple to disable RDRAND and RDSEED here.
22 */
 
23
24void x86_init_rdrand(struct cpuinfo_x86 *c)
25{
26	enum { SAMPLES = 8, MIN_CHANGE = 5 };
27	unsigned long sample, prev;
28	bool failure = false;
29	size_t i, changed;
30
31	if (!cpu_has(c, X86_FEATURE_RDRAND))
32		return;
33
34	for (changed = 0, i = 0; i < SAMPLES; ++i) {
35		if (!rdrand_long(&sample)) {
36			failure = true;
37			break;
 
38		}
39		changed += i && sample != prev;
40		prev = sample;
41	}
42	if (changed < MIN_CHANGE)
43		failure = true;
44
45	if (failure) {
46		clear_cpu_cap(c, X86_FEATURE_RDRAND);
47		clear_cpu_cap(c, X86_FEATURE_RDSEED);
48		pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
49	}
 
50}

 
 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
27static 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
42void 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}