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Diffstat (limited to 'arch/x86/kernel/cpu/rdrand.c')
| -rw-r--r-- | arch/x86/kernel/cpu/rdrand.c | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c new file mode 100644 index 000000000..c4be62058 --- /dev/null +++ b/arch/x86/kernel/cpu/rdrand.c @@ -0,0 +1,66 @@ +// 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 |