5 files changed, 83 insertions, 0 deletions

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 <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
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 <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
+}