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Index: head/sys/dev/random/ivy.c
===================================================================
--- head/sys/dev/random/ivy.c
+++ head/sys/dev/random/ivy.c
@@ -40,6 +40,7 @@
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/random.h>
+#include <sys/sysctl.h>
#include <sys/systm.h>
#include <machine/md_var.h>
@@ -59,23 +60,46 @@
.rs_read = random_ivy_read
};
+SYSCTL_NODE(_kern_random, OID_AUTO, rdrand, CTLFLAG_RW, 0,
+ "rdrand (ivy) entropy source");
+static bool acquire_independent_seed_samples = false;
+SYSCTL_BOOL(_kern_random_rdrand, OID_AUTO, rdrand_independent_seed,
+ CTLFLAG_RWTUN, &acquire_independent_seed_samples, 0,
+ "If non-zero, use more expensive and slow, but safer, seeded samples "
+ "where RDSEED is not present.");
+
static bool
x86_rdrand_store(u_long *buf)
{
- u_long rndval;
+ u_long rndval, seed_iterations, i;
int retry;
- retry = RETRY_COUNT;
- __asm __volatile(
- "1:\n\t"
- "rdrand %1\n\t" /* read randomness into rndval */
- "jc 2f\n\t" /* CF is set on success, exit retry loop */
- "dec %0\n\t" /* otherwise, retry-- */
- "jne 1b\n\t" /* and loop if retries are not exhausted */
- "2:"
- : "+r" (retry), "=r" (rndval) : : "cc");
+ /* Per [1], "§ 5.2.6 Generating Seeds from RDRAND,"
+ * machines lacking RDSEED will guarantee RDRAND is reseeded every 8kB
+ * of generated output.
+ *
+ * [1]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide#inpage-nav-6-8
+ */
+ if (acquire_independent_seed_samples)
+ seed_iterations = 8 * 1024 / sizeof(*buf);
+ else
+ seed_iterations = 1;
+
+ for (i = 0; i < seed_iterations; i++) {
+ retry = RETRY_COUNT;
+ __asm __volatile(
+ "1:\n\t"
+ "rdrand %1\n\t" /* read randomness into rndval */
+ "jc 2f\n\t" /* CF is set on success, exit retry loop */
+ "dec %0\n\t" /* otherwise, retry-- */
+ "jne 1b\n\t" /* and loop if retries are not exhausted */
+ "2:"
+ : "+r" (retry), "=r" (rndval) : : "cc");
+ if (retry == 0)
+ return (false);
+ }
*buf = rndval;
- return (retry != 0);
+ return (true);
}
static bool

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