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Diffstat (limited to 'arch/x86/kernel/cpu/rdrand.c')
-rw-r--r--arch/x86/kernel/cpu/rdrand.c25
1 files changed, 12 insertions, 13 deletions
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
index 136ac74de..819d94982 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
}