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66 lines
1.4 KiB
66 lines
1.4 KiB
// 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 <[email protected]>, |
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* H. Peter Anvin <[email protected]> |
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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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static int __init x86_rdrand_setup(char *s) |
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{ |
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setup_clear_cpu_cap(X86_FEATURE_RDRAND); |
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setup_clear_cpu_cap(X86_FEATURE_RDSEED); |
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return 1; |
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} |
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__setup("nordrand", x86_rdrand_setup); |
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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. |
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* If it fails, it is simple to disable RDRAND here. |
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*/ |
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#define SANITY_CHECK_LOOPS 8 |
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#ifdef CONFIG_ARCH_RANDOM |
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void x86_init_rdrand(struct cpuinfo_x86 *c) |
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{ |
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unsigned int changed = 0; |
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unsigned long tmp, prev; |
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int i; |
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if (!cpu_has(c, X86_FEATURE_RDRAND)) |
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return; |
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) { |
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if (!rdrand_long(&tmp)) { |
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clear_cpu_cap(c, X86_FEATURE_RDRAND); |
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pr_warn_once("rdrand: disabled\n"); |
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return; |
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} |
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} |
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/* |
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* Stupid sanity-check whether RDRAND does *actually* generate |
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* some at least random-looking data. |
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*/ |
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prev = tmp; |
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for (i = 0; i < SANITY_CHECK_LOOPS; i++) { |
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if (rdrand_long(&tmp)) { |
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if (prev != tmp) |
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changed++; |
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prev = tmp; |
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} |
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} |
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if (WARN_ON_ONCE(!changed)) |
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pr_emerg( |
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"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\""); |
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} |
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#endif
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