| 1 | // SPDX-License-Identifier: GPL-2.0-only |
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| 2 | /* |
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| 3 | * This file is part of the Linux kernel. |
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| 4 | * |
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| 5 | * Copyright (c) 2011, Intel Corporation |
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| 6 | * Authors: Fenghua Yu <fenghua.yu@intel.com>, |
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| 7 | * H. Peter Anvin <hpa@linux.intel.com> |
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| 8 | */ |
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| 9 | #include <linux/printk.h> |
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| 10 | |
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| 11 | #include <asm/processor.h> |
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| 12 | #include <asm/archrandom.h> |
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| 13 | #include <asm/sections.h> |
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| 14 | |
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| 15 | /* |
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| 16 | * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation. |
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| 17 | * Run the instruction a few times as a sanity check. Also make sure |
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| 18 | * it's not outputting the same value over and over, which has happened |
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| 19 | * as a result of past CPU bugs. |
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| 20 | * |
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| 21 | * If it fails, it is simple to disable RDRAND and RDSEED here. |
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| 22 | */ |
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| 23 | |
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| 24 | void x86_init_rdrand(struct cpuinfo_x86 *c) |
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| 25 | { |
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| 26 | enum { SAMPLES = 8, MIN_CHANGE = 5 }; |
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| 27 | unsigned long sample, prev; |
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| 28 | bool failure = false; |
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| 29 | size_t i, changed; |
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| 30 | |
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| 31 | if (!cpu_has(c, X86_FEATURE_RDRAND)) |
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| 32 | return; |
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| 33 | |
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| 34 | for (changed = 0, i = 0; i < SAMPLES; ++i) { |
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| 35 | if (!rdrand_long(v: &sample)) { |
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| 36 | failure = true; |
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| 37 | break; |
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| 38 | } |
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| 39 | changed += i && sample != prev; |
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| 40 | prev = sample; |
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| 41 | } |
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| 42 | if (changed < MIN_CHANGE) |
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| 43 | failure = true; |
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| 44 | |
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| 45 | if (failure) { |
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| 46 | clear_cpu_cap(c, X86_FEATURE_RDRAND); |
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| 47 | clear_cpu_cap(c, X86_FEATURE_RDSEED); |
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| 48 | pr_emerg("RDRAND is not reliable on this platform; disabling.\n" ); |
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| 49 | } |
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| 50 | } |
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| 51 | |
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