From 49d859d78c5aeb998b6936fcb5f288f78d713489 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Sun, 31 Jul 2011 14:02:19 -0700 Subject: [PATCH] x86, random: Verify RDRAND functionality and allow it to be disabled If the CPU declares that RDRAND is available, go through a guranteed reseed sequence, and make sure that it is actually working (producing data.) If it does not, disable the CPU feature flag. Allow RDRAND to be disabled on the command line (as opposed to at compile time) for a user who has special requirements with regards to random numbers. Signed-off-by: H. Peter Anvin Cc: Matt Mackall Cc: Herbert Xu Cc: "Theodore Ts'o" --- Documentation/kernel-parameters.txt | 5 ++ arch/x86/include/asm/archrandom.h | 2 + arch/x86/kernel/cpu/Makefile | 1 + arch/x86/kernel/cpu/common.c | 2 + arch/x86/kernel/cpu/rdrand.c | 73 +++++++++++++++++++++++++++++ 5 files changed, 83 insertions(+) create mode 100644 arch/x86/kernel/cpu/rdrand.c diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index aa47be71df4c..397ee05132a3 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1764,6 +1764,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. noresidual [PPC] Don't use residual data on PReP machines. + nordrand [X86] Disable the direct use of the RDRAND + instruction even if it is supported by the + processor. RDRAND is still available to user + space applications. + noresume [SWSUSP] Disables resume and restores original swap space. diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h index b7b5bc02e361..0d9ec770f2f8 100644 --- a/arch/x86/include/asm/archrandom.h +++ b/arch/x86/include/asm/archrandom.h @@ -70,4 +70,6 @@ GET_RANDOM(arch_get_random_int, unsigned int, RDRAND_INT, ASM_NOP3); #endif /* CONFIG_ARCH_RANDOM */ +extern void x86_init_rdrand(struct cpuinfo_x86 *c); + #endif /* ASM_X86_ARCHRANDOM_H */ diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile index 6042981d0309..0e3a82a41a66 100644 --- a/arch/x86/kernel/cpu/Makefile +++ b/arch/x86/kernel/cpu/Makefile @@ -15,6 +15,7 @@ CFLAGS_common.o := $(nostackp) obj-y := intel_cacheinfo.o scattered.o topology.o obj-y += proc.o capflags.o powerflags.o common.o obj-y += vmware.o hypervisor.o sched.o mshyperv.o +obj-y += rdrand.o obj-$(CONFIG_X86_32) += bugs.o obj-$(CONFIG_X86_64) += bugs_64.o diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 22a073d7fbff..8dbd9294f4f2 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include #include @@ -857,6 +858,7 @@ static void __cpuinit identify_cpu(struct cpuinfo_x86 *c) #endif init_hypervisor(c); + x86_init_rdrand(c); /* * Clear/Set all flags overriden by options, need do it diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c new file mode 100644 index 000000000000..feca286c2bb4 --- /dev/null +++ b/arch/x86/kernel/cpu/rdrand.c @@ -0,0 +1,73 @@ +/* + * This file is part of the Linux kernel. + * + * Copyright (c) 2011, Intel Corporation + * Authors: Fenghua Yu , + * H. Peter Anvin + * + * This program is free software; you can redistribute it and/or modify it + * under the terms and conditions of the GNU General Public License, + * version 2, as published by the Free Software Foundation. + * + * This program is distributed in the hope it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + * + * You should have received a copy of the GNU General Public License along with + * this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA. + * + */ + +#include +#include +#include + +static int __init x86_rdrand_setup(char *s) +{ + setup_clear_cpu_cap(X86_FEATURE_RDRAND); + return 1; +} +__setup("nordrand", x86_rdrand_setup); + +/* We can't use arch_get_random_long() here since alternatives haven't run */ +static inline int rdrand_long(unsigned long *v) +{ + int ok; + asm volatile("1: " RDRAND_LONG "\n\t" + "jc 2f\n\t" + "decl %0\n\t" + "jnz 1b\n\t" + "2:" + : "=r" (ok), "=a" (*v) + : "0" (RDRAND_RETRY_LOOPS)); + return ok; +} + +/* + * Force a reseed cycle; we are architecturally guaranteed a reseed + * after no more than 512 128-bit chunks of random data. This also + * acts as a test of the CPU capability. + */ +#define RESEED_LOOP ((512*128)/sizeof(unsigned long)) + +void __cpuinit x86_init_rdrand(struct cpuinfo_x86 *c) +{ +#ifdef CONFIG_ARCH_RANDOM + unsigned long tmp; + int i, count, ok; + + if (!cpu_has(c, X86_FEATURE_RDRAND)) + return; /* Nothing to do */ + + for (count = i = 0; i < RESEED_LOOP; i++) { + ok = rdrand_long(&tmp); + if (ok) + count++; + } + + if (count != RESEED_LOOP) + clear_cpu_cap(c, X86_FEATURE_RDRAND); +#endif +} -- 2.39.5