summaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/cpu/rdrand.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/kernel/cpu/rdrand.c')
-rw-r--r--arch/x86/kernel/cpu/rdrand.c49
1 files changed, 49 insertions, 0 deletions
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
new file mode 100644
index 0000000000..26a427fa84
--- /dev/null
+++ b/arch/x86/kernel/cpu/rdrand.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * 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>
+ */
+
+#include <asm/processor.h>
+#include <asm/archrandom.h>
+#include <asm/sections.h>
+
+/*
+ * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
+ * Run the instruction a few times as a sanity check. Also make sure
+ * it's not outputting the same value over and over, which has happened
+ * as a result of past CPU bugs.
+ *
+ * If it fails, it is simple to disable RDRAND and RDSEED here.
+ */
+
+void x86_init_rdrand(struct cpuinfo_x86 *c)
+{
+ enum { SAMPLES = 8, MIN_CHANGE = 5 };
+ unsigned long sample, prev;
+ bool failure = false;
+ size_t i, changed;
+
+ if (!cpu_has(c, X86_FEATURE_RDRAND))
+ return;
+
+ for (changed = 0, i = 0; i < SAMPLES; ++i) {
+ if (!rdrand_long(&sample)) {
+ failure = true;
+ break;
+ }
+ changed += i && sample != prev;
+ prev = sample;
+ }
+ if (changed < MIN_CHANGE)
+ failure = true;
+
+ if (failure) {
+ clear_cpu_cap(c, X86_FEATURE_RDRAND);
+ clear_cpu_cap(c, X86_FEATURE_RDSEED);
+ pr_emerg("RDRAND is not reliable on this platform; disabling.\n");
+ }
+}