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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>
/*
* RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
* Run the instruction a few times as a sanity check. Also make sure
* it's not outputting the same value over and over, which has happened
* as a result of past CPU bugs.
*
* If it fails, it is simple to disable RDRAND and RDSEED here.
*/
void x86_init_rdrand(struct cpuinfo_x86 *c)
{
enum { SAMPLES = 8, MIN_CHANGE = 5 };
unsigned long sample, prev;
bool failure = false;
size_t i, changed;
if (!cpu_has(c, X86_FEATURE_RDRAND))
return;
for (changed = 0, i = 0; i < SAMPLES; ++i) {
if (!rdrand_long(&sample)) {
failure = true;
break;
}
changed += i && sample != prev;
prev = sample;
}
if (changed < MIN_CHANGE)
failure = true;
if (failure) {
clear_cpu_cap(c, X86_FEATURE_RDRAND);
clear_cpu_cap(c, X86_FEATURE_RDSEED);
pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
}
}
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