Line data    Source code

       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             : 
      14           0 : static int __init x86_rdrand_setup(char *s)
      15             : {
      16           0 :         setup_clear_cpu_cap(X86_FEATURE_RDRAND);
      17           0 :         setup_clear_cpu_cap(X86_FEATURE_RDSEED);
      18           0 :         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
      30           4 : void x86_init_rdrand(struct cpuinfo_x86 *c)
      31             : {
      32           4 :         unsigned int changed = 0;
      33           4 :         unsigned long tmp, prev;
      34           4 :         int i;
      35             : 
      36           4 :         if (!cpu_has(c, X86_FEATURE_RDRAND))
      37           4 :                 return;
      38             : 
      39          36 :         for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
      40          64 :                 if (!rdrand_long(&tmp)) {
      41           0 :                         clear_cpu_cap(c, X86_FEATURE_RDRAND);
      42           0 :                         pr_warn_once("rdrand: disabled\n");
      43           0 :                         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          36 :         for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
      53          64 :                 if (rdrand_long(&tmp)) {
      54          32 :                         if (prev != tmp)
      55          32 :                                 changed++;
      56             : 
      57             :                         prev = tmp;
      58             :                 }
      59             :         }
      60             : 
      61           4 :         if (WARN_ON_ONCE(!changed))
      62           0 :                 pr_emerg(
      63             : "RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
      64             : 
      65             : }
      66             : #endif