1 // SPDX-License-Identifier: GPL-2.0-only
3 * This file is part of the Linux kernel.
5 * Copyright (c) 2011, Intel Corporation
6 * Authors: Fenghua Yu <fenghua.yu@intel.com>,
7 * H. Peter Anvin <hpa@linux.intel.com>
10 #include <asm/processor.h>
11 #include <asm/archrandom.h>
12 #include <asm/sections.h>
14 static int __init x86_rdrand_setup(char *s)
16 setup_clear_cpu_cap(X86_FEATURE_RDRAND);
17 setup_clear_cpu_cap(X86_FEATURE_RDSEED);
20 __setup("nordrand", x86_rdrand_setup);
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.
27 #define SANITY_CHECK_LOOPS 8
29 #ifdef CONFIG_ARCH_RANDOM
30 void x86_init_rdrand(struct cpuinfo_x86 *c)
32 unsigned int changed = 0;
33 unsigned long tmp, prev;
36 if (!cpu_has(c, X86_FEATURE_RDRAND))
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");
48 * Stupid sanity-check whether RDRAND does *actually* generate
49 * some at least random-looking data.
52 for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
53 if (rdrand_long(&tmp)) {
61 if (WARN_ON_ONCE(!changed))
63 "RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");