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Commit 49d859d7 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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: default avatarH. Peter Anvin <hpa@linux.intel.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "Theodore Ts'o" <tytso@mit.edu>
parent 628c6246

Documentation/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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.

arch/x86/include/asm/archrandom.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/cpu/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/cpu/common.c

+2 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <asm/stackprotector.h>

#include <asm/perf_event.h>

#include <asm/mmu_context.h>

#include <asm/archrandom.h>

#include <asm/hypervisor.h>

#include <asm/processor.h>

#include <asm/sections.h>
@@ -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

arch/x86/kernel/cpu/rdrand.c

0 → 100644
+73 −0
Original line number Diff line number Diff line 
/*

 * 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>

 *

 * 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 <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);

	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

}