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
10#include <asm/processor.h>
11#include <asm/archrandom.h>
12#include <asm/sections.h>
13
14static int __init x86_rdrand_setup(char *s)
15{
16	setup_clear_cpu_cap(X86_FEATURE_RDRAND);
17	setup_clear_cpu_cap(X86_FEATURE_RDSEED);
18	return 1;
19}
20__setup("nordrand", x86_rdrand_setup);
21
22/*
23 * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
24 * Run the instruction a few times as a sanity check.
25 * If it fails, it is simple to disable RDRAND here.
26 */
27#define SANITY_CHECK_LOOPS 8
28
29#ifdef CONFIG_ARCH_RANDOM
30void x86_init_rdrand(struct cpuinfo_x86 *c)
31{
32	unsigned long tmp;
 
33	int i;
34
35	if (!cpu_has(c, X86_FEATURE_RDRAND))
36		return;
37
38	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
39		if (!rdrand_long(&tmp)) {
40			clear_cpu_cap(c, X86_FEATURE_RDRAND);
41			pr_warn_once("rdrand: disabled\n");
42			return;
43		}
44	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
45}
46#endif

 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
10#include <asm/processor.h>
11#include <asm/archrandom.h>
12#include <asm/sections.h>
13
14static int __init x86_rdrand_setup(char *s)
15{
16	setup_clear_cpu_cap(X86_FEATURE_RDRAND);
17	setup_clear_cpu_cap(X86_FEATURE_RDSEED);
18	return 1;
19}
20__setup("nordrand", x86_rdrand_setup);
21
22/*
23 * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
24 * Run the instruction a few times as a sanity check.
25 * If it fails, it is simple to disable RDRAND here.
26 */
27#define SANITY_CHECK_LOOPS 8
28
29#ifdef CONFIG_ARCH_RANDOM
30void x86_init_rdrand(struct cpuinfo_x86 *c)
31{
32	unsigned int changed = 0;
33	unsigned long tmp, prev;
34	int i;
35
36	if (!cpu_has(c, X86_FEATURE_RDRAND))
37		return;
38
39	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
40		if (!rdrand_long(&tmp)) {
41			clear_cpu_cap(c, X86_FEATURE_RDRAND);
42			pr_warn_once("rdrand: disabled\n");
43			return;
44		}
45	}
46
47	/*
48	 * Stupid sanity-check whether RDRAND does *actually* generate
49	 * some at least random-looking data.
50	 */
51	prev = tmp;
52	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
53		if (rdrand_long(&tmp)) {
54			if (prev != tmp)
55				changed++;
56
57			prev = tmp;
58		}
59	}
60
61	if (WARN_ON_ONCE(!changed))
62		pr_emerg(
63"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
64
65}
66#endif