random + rdrand

arch/x86_64/meson.build

@@ -15,6 +15,7 @@ kernel_sources += files(
     'percpu.c',
     'pmap.c',
     'pmap.c',
+    'random.c',
     'sched.c',
     'serial.c',
     'smp.c',

arch/x86_64/random.c

@@ -0,0 +1,36 @@
+#include <zinnia/initgraph.h>
+#include <zinnia/print.h>
+#include <zinnia/random.h>
+#include <x86_64/asm.h>
+
+#define CPUID_1C_RDRAND (1u << 30)
+#define RDRAND_RETRIES  10
+
+static bool rdrand_get_u64(struct random_source*, uint64_t* out) {
+    for (int i = 0; i < RDRAND_RETRIES; i++) {
+        uint64_t value;
+        uint8_t ok;
+        asm volatile("rdrand %0\n setc %1" : "=r"(value), "=qm"(ok) : : "cc");
+        if (ok) {
+            *out = value;
+            return true;
+        }
+    }
+    return false;
+}
+
+static struct random_source rdrand_source = {
+    .name = "x86_64.rdrand",
+    .quality = 100,
+    .get_u64 = rdrand_get_u64,
+};
+
+static void rdrand_init(struct boot_info*) {
+    if (asm_cpuid(1, 0).ecx & CPUID_1C_RDRAND) {
+        random_register(&rdrand_source);
+    } else {
+        log_warn("random: This CPU doesn't support RDRAND, ignoring\n");
+    }
+}
+INIT_TASK(rdrand_stage, "arch.x86_64.rdrand", rdrand_init);
+INIT_ENTAILS(rdrand_stage, random_stage);