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