use ChaCha20Rng

Author: Sangho Lee

Cargo.lock

@@ -31,6 +31,8 @@ object = { version = "0.36.7", default-features = false, features = ["pe"] }
 digest = { version = "0.10.7", default-features = false }
 aligned-vec = { version = "0.6.4", default-features = false }
 raw-cpuid = "11.6.0"
+rand_chacha = { version = "0.3.1", default-features = false }
+rand_core = { version = "0.6.4", default-features = false }
 zerocopy = { version = "0.8", default-features = false, features = ["derive"] }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]

litebox_platform_lvbs/Cargo.toml

@@ -7,6 +7,7 @@ use crate::{
     Errno, HostInterface, arch::ioport::serial_print_string,
     host::per_cpu_variables::with_per_cpu_variables,
 };
+use rand_core::{RngCore, SeedableRng};
 
 pub type LvbsLinuxKernel = crate::LinuxKernel<HostLvbsInterface>;
 
@@ -102,16 +103,31 @@ unsafe impl litebox::platform::ThreadLocalStorageProvider for LvbsLinuxKernel {
 
 impl litebox::platform::CrngProvider for LvbsLinuxKernel {
     fn fill_bytes_crng(&self, buf: &mut [u8]) {
-        // FIXME: generate real random data.
-        static RANDOM: spin::mutex::SpinMutex<litebox::utils::rng::FastRng> =
-            spin::mutex::SpinMutex::new(litebox::utils::rng::FastRng::new_from_seed(
-                core::num::NonZeroU64::new(0x4d595df4d0f33173).unwrap(),
-            ));
+        static RANDOM: spin::mutex::SpinMutex<Option<rand_chacha::ChaCha20Rng>> =
+            spin::mutex::SpinMutex::new(None);
+
         let mut random = RANDOM.lock();
-        for b in buf.chunks_mut(8) {
-            b.copy_from_slice(&random.next_u64().to_ne_bytes()[..b.len()]);
+        random
+            .get_or_insert_with(|| rand_chacha::ChaCha20Rng::from_seed(rdrand_seed()))
+            .fill_bytes(buf);
+    }
+}
+
+fn rdrand_seed() -> <rand_chacha::ChaCha20Rng as SeedableRng>::Seed {
+    let mut seed = <rand_chacha::ChaCha20Rng as SeedableRng>::Seed::default();
+    for chunk in seed.chunks_mut(8) {
+        let mut word = 0;
+        loop {
+            // Safety: `RDRAND` is available on the LVBS target CPUs. A false
+            // carry flag means random data is temporarily unavailable.
+            if unsafe { core::arch::x86_64::_rdrand64_step(&mut word) } == 1 {
+                break;
+            }
+            core::hint::spin_loop();
         }
+        chunk.copy_from_slice(&word.to_ne_bytes()[..chunk.len()]);
     }
+    seed
 }
 
 pub struct HostLvbsInterface;