| // 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> | |
| static int __init x86_rdrand_setup(char *s) | |
| { | |
| setup_clear_cpu_cap(X86_FEATURE_RDRAND); | |
| setup_clear_cpu_cap(X86_FEATURE_RDSEED); | |
| return 1; | |
| } | |
| __setup("nordrand", x86_rdrand_setup); | |
| /* | |
| * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation. | |
| * Run the instruction a few times as a sanity check. | |
| * If it fails, it is simple to disable RDRAND here. | |
| */ | |
| #define SANITY_CHECK_LOOPS 8 | |
| #ifdef CONFIG_ARCH_RANDOM | |
| void x86_init_rdrand(struct cpuinfo_x86 *c) | |
| { | |
| unsigned int changed = 0; | |
| unsigned long tmp, prev; | |
| int i; | |
| if (!cpu_has(c, X86_FEATURE_RDRAND)) | |
| return; | |
| for (i = 0; i < SANITY_CHECK_LOOPS; i++) { | |
| if (!rdrand_long(&tmp)) { | |
| clear_cpu_cap(c, X86_FEATURE_RDRAND); | |
| pr_warn_once("rdrand: disabled\n"); | |
| return; | |
| } | |
| } | |
| /* | |
| * Stupid sanity-check whether RDRAND does *actually* generate | |
| * some at least random-looking data. | |
| */ | |
| prev = tmp; | |
| for (i = 0; i < SANITY_CHECK_LOOPS; i++) { | |
| if (rdrand_long(&tmp)) { | |
| if (prev != tmp) | |
| changed++; | |
| prev = tmp; | |
| } | |
| } | |
| if (WARN_ON_ONCE(!changed)) | |
| pr_emerg( | |
| "RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\""); | |
| } | |
| #endif |