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");
+	}
+}