1 files changed, 12 insertions, 13 deletions

diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
index 136ac74dee82..819d94982e07 100644
--- a/arch/x86/kernel/cpu/rdrand.c
+++ b/arch/x86/kernel/cpu/rdrand.c
@@ -33,28 +33,27 @@ static int __init x86_rdrand_setup(char *s)
 __setup("nordrand", x86_rdrand_setup);
 
 /*
- * 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.
+ * RDRAND has Built-In-Self-Test (BIST) that runs on every invocation.
+ * Run the instruction a few times as a sanity check.
+ * If it fails, it is simple to disable RDRAND here.
  */
-#define RESEED_LOOP ((512*128)/sizeof(unsigned long))
+#define SANITY_CHECK_LOOPS 8
 
 void x86_init_rdrand(struct cpuinfo_x86 *c)
 {
 #ifdef CONFIG_ARCH_RANDOM
         unsigned long tmp;
-        int i, count, ok;
+        int i;
 
         if (!cpu_has(c, X86_FEATURE_RDRAND))
-                return;         /* Nothing to do */
+                return;
 
-        for (count = i = 0; i < RESEED_LOOP; i++) {
-                ok = rdrand_long(&tmp);
-                if (ok)
-                        count++;
+        for (i = 0; i < SANITY_CHECK_LOOPS; i++) {
+                if (!rdrand_long(&tmp)) {
+                        clear_cpu_cap(c, X86_FEATURE_RDRAND);
+                        printk_once(KERN_WARNING "rdrand: disabled\n");
+                        return;
+                }
         }
-
-        if (count != RESEED_LOOP)
-                clear_cpu_cap(c, X86_FEATURE_RDRAND);
 #endif
 }