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| 2 | |
| 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 <[email protected]>,
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| 7 | * H. Peter Anvin <[email protected]>
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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 | |
| 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(&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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