cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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rdrand.c (1468B)

      1// SPDX-License-Identifier: GPL-2.0-only
      2/*
      3 * This file is part of the Linux kernel.
      4 *
      5 * Copyright (c) 2011, Intel Corporation
      6 * Authors: Fenghua Yu <fenghua.yu@intel.com>,
      7 *          H. Peter Anvin <hpa@linux.intel.com>
      8 */
      9
     10#include <asm/processor.h>
     11#include <asm/archrandom.h>
     12#include <asm/sections.h>
     13
     14static int __init x86_rdrand_setup(char *s)
     15{
     16	setup_clear_cpu_cap(X86_FEATURE_RDRAND);
     17	setup_clear_cpu_cap(X86_FEATURE_RDSEED);
     18	return 1;
     19}
     20__setup("nordrand", x86_rdrand_setup);
     21
     22/*
     23 * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
     24 * Run the instruction a few times as a sanity check.
     25 * If it fails, it is simple to disable RDRAND here.
     26 */
     27#define SANITY_CHECK_LOOPS 8
     28
     29#ifdef CONFIG_ARCH_RANDOM
     30void x86_init_rdrand(struct cpuinfo_x86 *c)
     31{
     32	unsigned int changed = 0;
     33	unsigned long tmp, prev;
     34	int i;
     35
     36	if (!cpu_has(c, X86_FEATURE_RDRAND))
     37		return;
     38
     39	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
     40		if (!rdrand_long(&tmp)) {
     41			clear_cpu_cap(c, X86_FEATURE_RDRAND);
     42			pr_warn_once("rdrand: disabled\n");
     43			return;
     44		}
     45	}
     46
     47	/*
     48	 * Stupid sanity-check whether RDRAND does *actually* generate
     49	 * some at least random-looking data.
     50	 */
     51	prev = tmp;
     52	for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
     53		if (rdrand_long(&tmp)) {
     54			if (prev != tmp)
     55				changed++;
     56
     57			prev = tmp;
     58		}
     59	}
     60
     61	if (WARN_ON_ONCE(!changed))
     62		pr_emerg(
     63"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
     64
     65}
     66#endif