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	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 */
35static 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
55void __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}

 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
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
14/*
15 * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
16 * Run the instruction a few times as a sanity check. Also make sure
17 * it's not outputting the same value over and over, which has happened
18 * as a result of past CPU bugs.
19 *
20 * If it fails, it is simple to disable RDRAND and RDSEED here.
21 */
 
22
23void x86_init_rdrand(struct cpuinfo_x86 *c)
24{
25	enum { SAMPLES = 8, MIN_CHANGE = 5 };
26	unsigned long sample, prev;
27	bool failure = false;
28	size_t i, changed;
29
30	if (!cpu_has(c, X86_FEATURE_RDRAND))
31		return;
32
33	for (changed = 0, i = 0; i < SAMPLES; ++i) {
34		if (!rdrand_long(&sample)) {
35			failure = true;
36			break;
37		}
38		changed += i && sample != prev;
39		prev = sample;
40	}
41	if (changed < MIN_CHANGE)
42		failure = true;
43
44	if (failure) {
45		clear_cpu_cap(c, X86_FEATURE_RDRAND);
46		clear_cpu_cap(c, X86_FEATURE_RDSEED);
47		pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
48	}
49}