This is a note to let you know that I've just added the patch titled
x86, random: Verify RDRAND functionality and allow it to be disabled
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-random-verify-rdrand-functionality-and-allow-it-to-be-disabled.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 49d859d78c5aeb998b6936fcb5f288f78d713489 Mon Sep 17 00:00:00 2001
From: "H. Peter Anvin" <[email protected]>
Date: Sun, 31 Jul 2011 14:02:19 -0700
Subject: x86, random: Verify RDRAND functionality and allow it to be disabled
From: "H. Peter Anvin" <[email protected]>
commit 49d859d78c5aeb998b6936fcb5f288f78d713489 upstream.
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 <[email protected]>
Cc: Matt Mackall <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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(+)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1764,6 +1764,11 @@ bytes respectively. Such letter suffixes
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.
--- 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
#endif /* CONFIG_ARCH_RANDOM */
+extern void x86_init_rdrand(struct cpuinfo_x86 *c);
+
#endif /* ASM_X86_ARCHRANDOM_H */
--- 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
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -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>
@@ -852,6 +853,7 @@ static void __cpuinit identify_cpu(struc
#endif
init_hypervisor(c);
+ x86_init_rdrand(c);
/*
* Clear/Set all flags overriden by options, need do it
--- /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 <[email protected]>,
+ * H. Peter Anvin <[email protected]>
+ *
+ * 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
+}
Patches currently in stable-queue which might be from [email protected] are
queue-3.0/x86-random-verify-rdrand-functionality-and-allow-it-to-be-disabled.patch
queue-3.0/x86-random-architectural-inlines-to-get-random-integers-with-rdrand.patch
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