50 lines
1.2 KiB
C
50 lines
1.2 KiB
C
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// 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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/*
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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. Also make sure
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* it's not outputting the same value over and over, which has happened
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* as a result of past CPU bugs.
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*
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* If it fails, it is simple to disable RDRAND and RDSEED here.
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*/
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void x86_init_rdrand(struct cpuinfo_x86 *c)
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{
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enum { SAMPLES = 8, MIN_CHANGE = 5 };
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unsigned long sample, prev;
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bool failure = false;
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size_t i, changed;
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if (!cpu_has(c, X86_FEATURE_RDRAND))
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return;
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for (changed = 0, i = 0; i < SAMPLES; ++i) {
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if (!rdrand_long(&sample)) {
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failure = true;
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break;
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}
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changed += i && sample != prev;
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prev = sample;
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}
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if (changed < MIN_CHANGE)
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failure = true;
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if (failure) {
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clear_cpu_cap(c, X86_FEATURE_RDRAND);
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clear_cpu_cap(c, X86_FEATURE_RDSEED);
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pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
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}
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}
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