// SPDX-License-Identifier: GPL-2.0-only
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/*
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* This file is part of the Linux kernel.
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*
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* Copyright (c) 2011, Intel Corporation
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* Authors: Fenghua Yu <fenghua.yu@intel.com>,
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* H. Peter Anvin <hpa@linux.intel.com>
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*/
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#include <asm/processor.h>
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#include <asm/archrandom.h>
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#include <asm/sections.h>
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static int __init x86_rdrand_setup(char *s)
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{
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setup_clear_cpu_cap(X86_FEATURE_RDRAND);
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setup_clear_cpu_cap(X86_FEATURE_RDSEED);
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return 1;
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}
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__setup("nordrand", x86_rdrand_setup);
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/*
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* RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
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* Run the instruction a few times as a sanity check.
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* If it fails, it is simple to disable RDRAND here.
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*/
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#define SANITY_CHECK_LOOPS 8
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#ifdef CONFIG_ARCH_RANDOM
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void x86_init_rdrand(struct cpuinfo_x86 *c)
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{
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unsigned int changed = 0;
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unsigned long tmp, prev;
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int i;
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if (!cpu_has(c, X86_FEATURE_RDRAND))
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return;
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
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if (!rdrand_long(&tmp)) {
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clear_cpu_cap(c, X86_FEATURE_RDRAND);
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pr_warn_once("rdrand: disabled\n");
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return;
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}
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}
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/*
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* Stupid sanity-check whether RDRAND does *actually* generate
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* some at least random-looking data.
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*/
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prev = tmp;
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
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if (rdrand_long(&tmp)) {
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if (prev != tmp)
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changed++;
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prev = tmp;
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}
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}
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if (WARN_ON_ONCE(!changed))
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pr_emerg(
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"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
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}
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#endif
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