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// 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}