| H. Peter Anvin | 49d859d | 2011-07-31 14:02:19 -0700 | [diff] [blame] | 1 | /* |
| 2 | * This file is part of the Linux kernel. |
| 3 | * |
| 4 | * Copyright (c) 2011, Intel Corporation |
| 5 | * Authors: Fenghua Yu <fenghua.yu@intel.com>, |
| 6 | * H. Peter Anvin <hpa@linux.intel.com> |
| 7 | * |
| 8 | * This program is free software; you can redistribute it and/or modify it |
| 9 | * under the terms and conditions of the GNU General Public License, |
| 10 | * version 2, as published by the Free Software Foundation. |
| 11 | * |
| 12 | * This program is distributed in the hope it will be useful, but WITHOUT |
| 13 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 14 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
| 15 | * more details. |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License along with |
| 18 | * this program; if not, write to the Free Software Foundation, Inc., |
| 19 | * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | */ |
| 22 | |
| 23 | #include <asm/processor.h> |
| 24 | #include <asm/archrandom.h> |
| 25 | #include <asm/sections.h> |
| 26 | |
| 27 | static int __init x86_rdrand_setup(char *s) |
| 28 | { |
| 29 | setup_clear_cpu_cap(X86_FEATURE_RDRAND); |
| 30 | return 1; |
| 31 | } |
| 32 | __setup("nordrand", x86_rdrand_setup); |
| 33 | |
| 34 | /* We can't use arch_get_random_long() here since alternatives haven't run */ |
| 35 | static inline int rdrand_long(unsigned long *v) |
| 36 | { |
| 37 | int ok; |
| 38 | asm volatile("1: " RDRAND_LONG "\n\t" |
| 39 | "jc 2f\n\t" |
| 40 | "decl %0\n\t" |
| 41 | "jnz 1b\n\t" |
| 42 | "2:" |
| 43 | : "=r" (ok), "=a" (*v) |
| 44 | : "0" (RDRAND_RETRY_LOOPS)); |
| 45 | return ok; |
| 46 | } |
| 47 | |
| 48 | /* |
| 49 | * Force a reseed cycle; we are architecturally guaranteed a reseed |
| 50 | * after no more than 512 128-bit chunks of random data. This also |
| 51 | * acts as a test of the CPU capability. |
| 52 | */ |
| 53 | #define RESEED_LOOP ((512*128)/sizeof(unsigned long)) |
| 54 | |
| 55 | void __cpuinit x86_init_rdrand(struct cpuinfo_x86 *c) |
| 56 | { |
| 57 | #ifdef CONFIG_ARCH_RANDOM |
| 58 | unsigned long tmp; |
| 59 | int i, count, ok; |
| 60 | |
| 61 | if (!cpu_has(c, X86_FEATURE_RDRAND)) |
| 62 | return; /* Nothing to do */ |
| 63 | |
| 64 | for (count = i = 0; i < RESEED_LOOP; i++) { |
| 65 | ok = rdrand_long(&tmp); |
| 66 | if (ok) |
| 67 | count++; |
| 68 | } |
| 69 | |
| 70 | if (count != RESEED_LOOP) |
| 71 | clear_cpu_cap(c, X86_FEATURE_RDRAND); |
| 72 | #endif |
| 73 | } |